BTO - British Trust for Ornithology - Science

Sharing our gull tracking expertise in a study of Dublin’s ‘noisy neighbours’

WEBSITEEDITOR — Fri, 15 Dec 2023 10:40:29 +0000

PhD student Jon Willans takes us through his fascination with gulls and his fieldwork, which was supported by our scientists. No

Jon Willans PhD student at University College Dublin

Jon has been studying and working with birds for the past 16 years in his native Canada, as well as in Ireland, the USA, Costa Rica, Uzbekistan and the UK.

These are just some of the comments I have heard after people learn that I am a PhD student studying the movement ecology of urban gulls. It turns out that, apparently, not everyone likes gulls or finds them as interesting as I do.

Here in Dublin, like in many coastal cities around Ireland and the UK, there has been a noticeable increase in the number of nesting gulls over the past 30 years. Unfortunately for the gulls, they haven’t been universally welcomed with open arms.

Some human residents feel that the addition of gulls to urban areas should be looked at as a cause for concern and outrage, rather than celebrated as a boost to gull populations — despite drastic declines in gull numbers that have led to some species being listed as of significant conservation concern in Ireland. And human–gull conflict is a growing issue in some cities, where officials are increasingly being pressured into action to control bird numbers by means such as egg oiling, nest removal and even culling.

But, as urban-nesting gulls are a relatively new phenomenon, little is known about how these birds are using these urban environments. Do urban-nesting birds even use the sea? Do they leave the city at all? How does their movement differ from ‘natural’ coastal nesting gulls? Do these coastal-nesting birds generally use the marine habitat for foraging, or do they also spend large amounts of time in the city to find food? The answers to these questions are extremely important when it comes to making any decisions about gull population management.

Urban nesting gulls are a relatively new phenomenon, so little is known about how these birds are using their environment.

An introduction to our research

It was these questions which brought our team, consisting of researchers from University College Dublin (UCD), BirdWatch Ireland, the Irish Midlands Ringing Group and the British Trust for Ornithology, to Ireland at the end of May, to try and shed some light on the movement of locally breeding Herring Gulls.

Specifically, in this study, we wanted to investigate whether there is a difference in the movement ecology — how birds navigate through habitats, and where they go — between birds nesting in urban spaces and on islands around the coast. To determine this, we needed to find both an inland colony and a coastal colony of nesting gulls, and attach GPS units to individual birds. We could then analyse data from birds in the two colony locations to see if or how these birds differ in their use of Dublin’s urban landscape.

Tracking urban gulls ...

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The UCD campus hosts several roof-nesting groups of gulls.

The first stop for the team was the UCD campus in south Dublin — our urban study site — where a small but increasing community of Herring and Lesser Black-backed Gulls can be found nesting on many of the rooftops around the university. While this type of environment is not traditionally associated with ideal habitat for nesting gulls, when you look closer you notice that the campus has everything that the gulls might require.

The tall buildings act as cliffs, where gulls can make their nests with an unobstructed view of their environment, safe from most predators. The many ponds and sports fields on and around the campus provide an ample amount of water and natural feeding opportunities.

A plentiful supply of food is also provided by the thousands of students and staff that make the daily trip onto the campus. On any given day, particularly when the sun is shining, hundreds of people can be found sitting outside eating. Gulls are often fed by these people, but they are also known to snatch food from unsuspecting diners when their hints for a snack are not being met accordingly. The gulls also feast on the mess that is left behind after people have moved on, which sometimes includes pulling rubbish from bins in search of a quick meal. Indeed, some may say this is an urban sanctuary for these birds.

The goal of our team was to catch some of the local birds and attach lightweight GPS units to them, which would give us some information about how these birds are using their environments.

The goal of our team was to catch some of the local birds and attach lightweight GPS units to them, which would give us some information about how these birds are using their urban environments. Over the next two days, working on four different rooftops and spending a considerable amount of time waiting for the unsuspecting birds to walk into the carefully placed, specialist traps, we managed to catch six breeding Herring Gulls.

Once we had taken the birds safely out of the traps, the team went into action. The birds were weighed, and we collected morphometric data like wing, bill and head length. Then we attached uniquely coded rings to their legs and fitted them with their solar-powered GPS units. These units gather and transmit data about the birds’ location and movement speed, which we can use to identify the birds’ behaviours — such as foraging, feeding or resting — as the birds navigate around the landscape.

With six tags deployed and each one actively collecting data, stage one of this mission was complete. We had tagged our urban birds.

... and coastal gulls

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Jon conducting fieldwork on Dalkey Island, the coastal study site.

Stage two involved moving operations to Dalkey Island, some 10 km to the south-east of UCD as the gull flies.

Although the island is only separated from the mainland by approximately 350 m, after getting off the ferry it felt like stepping into another world. From the herd of Old Irish goats that stopped their grazing to observe us as we arrived on their island, to the sound of the breeding gulls and the buzzing Arctic Terns that nest there, it couldn't have been further removed from the university campus.

Dalkey Island is a more traditional place to find breeding gulls: a rocky coastal area with some scrubby turf and thrift, and plenty of nooks and ledges to make a scrape-like nest. The island has large nesting colonies of Herring, Great Black-backed and Lesser Black-backed Gulls, and when we visited, pairs were scattered all across the island’s east side. Segregated zones marked the presence of the different species: while the massive and intimidating Great Black-backs watched from up high on the grassy slopes, the Herring Gulls were lower down and mainly confined to the rocky areas near the shore and the Lesser Black-backs were scattered at the north end of the colony.

We set more traps and over the next two days, seven more Herring Gulls were caught and selected to collect data for us, fitted with GPS units and sent on their way. Now we had our coastal nesting birds as well. Job done! Well, almost ...

What will we learn about Dublin’s ‘noisy neighbours’?

Early data returns from the GPS units show that there may well be differences in the way these groups of birds behave and use the urban landscape.

Over the next two years, all the GPS tags that the team has worked so hard, and suffered so many bitten fingers, to deploy will be transmitting data back to us and revealing just exactly how the gulls spend their time as they move around this country and perhaps even further afield.

The next step in the research involves analysing all this information. Early data returns from the GPS units show that there may well be differences in the way the urban- and coastal-nesting birds behave and use the urban landscape. As expected, both groups of birds spend a great deal of time inland, visiting the downtown core and the suburbs around the city. However, one initial difference appears to be the birds’ use of the sea: coastal nesting birds make frequent feeding trips out to sea, while the urban nesting birds seldom use this resource and appear to be full-time city dwellers.

Map showing tracks of 13 GPS-tagged Herring Gulls from UCD Campus (yellow square) and Dalkey Island (pink square) between 25–30 May 2023.

Is the sea in ‘seagull’ even applicable to all of these birds? As the data they have unknowingly collected are analysed, all will be revealed — and I for one cannot wait.

The tags deployed over this week of fieldwork will continue to record the movements of these gulls until the specially-designed harnesses break apart and relieve the birds of their GPS units.

What secrets will these data reveal? Is the sea in ‘seagull’ even applicable to all of these birds? These secrets will remain with our gulls for the meantime, but soon, as these birds move around on their daily adventures and the data they have unknowingly collected are analysed, all will be revealed — and I for one cannot wait.

Help us monitor gulls this winter

If you are confident identifying the six main species of gull found in the UK in winter — Herring, Lesser Black-backed, Great Black-backed, Black-headed, Common and Mediterranean — you could join our Winter Gull Survey.

Volunteers will only need to make a small number of visits to gull roosts between 2023 and 2025, but their contributions will help us fill in vital gaps in our understanding of these Amber- and Red-listed species.

How to take part in WinGS

PhD student Jon Willans takes us through his fascination with gulls and his fieldwork, which was supported by our scientists.

1 December 2023

“Why would you want to study seagulls?”
“Those birds are pests — they don’t even belong in cities.”
“They are so noisy!”

15 Dec 2023

Ireland

Arctic Skua migration: stories from the field

WEBSITEEDITOR — Fri, 13 Oct 2023 16:18:50 +0000

Where do Arctic Skuas go when they are not in Scotland? Helen and David Aiton take us through their fieldwork seasons for BTO’s Arctic Skua tracking project, which has followed these fascinating birds across both hemispheres and back. No

Helen and David Aiton

Helen and David Aiton have been members of BTO for over 40 years. Over this period, they have contributed to many BTO surveys and currently have a Breeding Bird Survey site on Rousay.

We were drawn to these beautiful birds by their plaintive calls, their stunning range of plumages and – sadly – their rapid population decline. In 1991, there were 122 pairs in our study area along with thousands of Arctic Terns. Now, in 2023, there are only 17 Arctic Skua pairs and a mere handful of breeding Arctic Terns. This trend reflects that of the UK breeding population more broadly, which is restricted to north and west Scotland and has declined by 70% since 2000.

Our fieldwork site is a triangular area of coastal moorland approximately 2 km by 1.5 km and varies from 5–115 m above sea level. We also research Great Skuas in our study area – but that is a story for another time! The aim of our long-term study is to monitor how both skua species are faring in these turbulent times.

This year, 2023, was the 10th season of our Arctic Skua productivity study, which measures the breeding success of the colony. We collect information about the number of eggs, chicks and fledged young every breeding season. Over the past 10 years, our colony has fledged 96 juvenile birds.

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A newly hatched Arctic Skua chick with its ‘egg tooth’, a sharp point on its beak that helps the chick to break the eggshell from the inside when it is ready to hatch. The egg tooth falls off the beak around a day after hatching.

Fieldwork on Rousay

Each year we visit the study area at least eight times, an effort of 16 days minimum. The island can be reached by a 30-minute ferry trip, crossing the beautiful Eynhallow Sound. Our fieldwork is made more comfortable in our old VW Campervan for overnight stays.

We locate nests at the start of each breeding season from vantage points at least 200 metres away: one person remains at the vantage point and directs the other using radios, to as many as five nests at a time. Arctic Skua nests are well hidden, so we have to use sightlines and surrounding vegetation to memorise their positions, so we can monitor them throughout the season.

Arctic Skua nests are well hidden, so we have to use sightlines and surrounding vegetation to memorise their positions.

We also use our two highly-trained German Shorthaired Pointers to increase the efficiency of finding chicks which have become more mobile and might have wandered away from the nest. It’s very important that we only undertake nest and chick finding in dry, warm weather to avoid the risk of causing any harm due to chilling.

The Arctic Skua tracking project

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Helen holding an adult bird ready for release. The geolocator is attached to the uniquely-coded orange ring on the Arctic Skua’s left leg.

Liz Humphreys from BTO Scotland contacted us in 2018, having heard about our well-established study. BTO’s scientists were keen to use geolocators to track the adult Arctic Skuas, to find out where they spent their winters, and to learn more about their migration routes. This information would help inform conservation efforts to protect this species. The work on Rousay would build on the study of Fair Isle breeding Arctic Skuas, which BTO began in 2017, and offer a comparator site. Fair Isle is roughly 30 miles from Orkney.

BTO’s Senior Research Ecologist John Callandine joined us for a week on Rousay, arriving in late May 2018. Luckily for John, we had a week of hot, dry and still weather, almost unknown in Orkney – highly suitable conditions for checking nests and catching adult birds for tagging. He was delighted that we had already located the nesting birds.

Luckily, we had a week of hot, dry and still weather, almost unknown in Orkney – highly suitable conditions for checking nests and catching adult birds for tagging.

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John (left) and David (right) place a walk-in trap over dummy eggs in the nest cup. The real eggs are safely stored in the box John is holding.

For the tagging project, we chose mostly well-established pairs of adult birds. Over the next few days, we watched the birds and waited for them to lay a full clutch of eggs. We then prepared the walk-in traps – safe structures for catching the adult birds – and left them for a couple of days near the nests, to habituate the birds to them.

Eventually, we placed the traps over the nests, to catch the adults as they walked onto the nest to incubate the eggs. To keep the eggs safe from predators while we tagged the adults, we removed them temporarily and replaced them with dummy eggs before putting the walk-in trap over the nest.

John had honed the techniques for catching birds on Fair Isle the year before, so we were a slick team! We caught 10 individual birds, two of which were a pair. As soon as the tagging was finished we replaced the real eggs. The whole process never took more than an hour.

John then left Rousay to go to Fair Isle to catch more birds, and we continued our study for the rest of the summer. It was reassuring that the birds with geolocators continued to behave normally, with most of them rearing chicks successfully that year.

Collecting the geolocator data

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Arctic Skua plumage falls broadly into two ‘phases’: pale phase (as in the bird in the top photograph) and dark phase (as in the bird in the bottom photograph). Plumage which is intermediate between these phases can also occur in some birds.

Using geolocators as a tool to understand migration routes does not provide instant gratification. To collect the data from the geolocators, they have to be retrieved from the birds, which meant we had to catch the tagged birds again to get any information at all! Innocent of the wiles and intelligence of Arctic Skuas we returned to Rousay in late spring 2019, keenly anticipating retrieving the geolocators and continuing our productivity study.

John joined us again in early June to begin the retrieval process and repeat the procedure using the walk-in traps. However, of the 10 birds we caught in 2018, only eight birds had returned, and one of the birds that did return tried to breed, but her nest failed before we had a chance to try to recapture her with the walk-in traps – down to seven birds.

Arctic Skuas share incubation duties, with both the male and the female sitting on eggs. Because individual Arctic Skuas can occur in one of two plumage types – birds are either ‘dark’ or ‘pale’ phase – we could tell the male and female apart if they had different phase plumage, what we called a ‘dark-pale phase pair combination’. But for a dark-dark phase pair combination, where only one of the pair was carrying a geolocator, we had to take extra care to ensure we were catching the right bird.

The first bird we tried to catch, a female pale-phase bird, walked straight into the walk-in trap and onto the dummy eggs – hurrah – Geolocator Number 1. After this, we thought – this was going to be easy! Alas not. That was the only geolocator retrieved during John’s visit, despite trying for the remaining six birds who all refused to go back into a walk-in trap.

Later in June, we tried mist-netting one pair that had a young chick. A mist net is a fine mesh held taut between two vertical poles, which we can use to safely catch birds by encouraging them to fly or walk into it (in this case, by placing a stuffed predator close by to the net in the hope that the adult birds would fly into the net while mobbing it) but the adults very cleverly called the chick away from the net instead. Sigh!

We were fortunate that one pair – which had had a single egg predated by a neighbouring Arctic Skua (quite common in the skua colonies) – re-laid, and had a young chick less than a week old in late July. With both adults close to their nest, we had the opportunity to try recatching them, and this time both threw themselves into the mist net at the same time! Geolocator Number 2 retrieved.

As in 2018, the colony went on to successfully fledge chicks, including that late chick.

A brief hiatus ...

Due to COVID-19 restrictions in 2020, we were not able to return to Rousay until early July, by which time the chicks were too old for us to try to catch the adults with a mist net. Again, though, it was a good year for the Arctic Skuas and they fledged at least 10 chicks.

... before fieldwork resumed

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John (left) and David (right) relaxing on the Rousay pier after fieldwork was complete.

In 2021, three years after putting the geolocators on the birds, John joined us again in glorious weather in early June. There were still four birds with geolocators breeding in the colony. We successfully mist-netted a female using dummy eggs and a stuffed predator, which she duly mobbed and entered the mist net – Geolocator Number 3 retrieved.

John and David worked very hard to retrieve the remaining three geolocators, but the birds refused to engage with the walk-in traps or the mist nets. Later in June, we tried again with the dark-phase male mate of the first pale-phase bird we retrapped in 2019 – and success! – he eventually walked into the trap and settled on the dummy eggs – Geolocator Number 4. We hoped at the very least that the birds we recaught to retrieve the geolocators this year would give us two years’ worth of migration information.

Finally, after approximately 200 hours of effort, we had four geolocators retrieved, along with six geolocators from John’s work on Fair Isle. The BTO team could set about retrieving the data from the geolocators and plotting the migration routes of the 10 Arctic Skuas. It is no exaggeration that we were all thrilled to see the results.

Migration stories revealed

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Circles show the different wintering locations of individual Arctic Skuas, each of which is represented by a different colour. Two circles of the same colour represent the wintering locations of the same bird in consecutive winters. Different birds from the same breeding colony spent our winter months off the coast of north-west Africa, south-west Africa, or the east coast of South America. The triangle shows the location of Rousay, Orkney, where the Arctic Skuas breed.

The data showed that all the Arctic Skuas travelled south via the North Sea and English Channel. Then down past France, Spain and Portugal to the coast of north-west Africa and on to their wintering grounds.

Individual Arctic Skuas wintered in different locations: off the coast of north-west Africa, the coast of south-west Africa or the east coast of South America. The accuracy of the data is roughly to the nearest 200 km so the birds are not actually on land, as can appear in the maps of the location points – they overwinter at sea. The birds that had data over two winters went back to the same area each year. Astonishingly, our pair of birds that both had geolocators went to different continents!

The work we did in Scotland will also be part of a multi-colony study of Arctic Skua wintering and migration movement involving colonies right across their north-east Atlantic breeding range – some of which was presented by BTO Senior Research Ecologist Nina O’Hanlon to the International Seabird Group Conference in Cork in September 2022 and has now been submitted for peer review. You can read more about the project’s findings in Nina’s blog.

It is rewarding to see the work we contributed to being part of a published international study. Even two years after the maps were produced, it is still deeply satisfying to be able to visualise the journeys of the Arctic Skuas when they are not on Rousay.

Since the Arctic Skua research programme was established in 2017, BTO donors have donated more than £225,000 to fund the work. We are enormously grateful for this very generous support from a small number of committed individuals. The research could not have been delivered without this funding. We would also like to thank the Scottish Ornithologists’ Club for annual grants that cover the cost of the productivity study on Rousay.

World Migratory Bird Day 2023

This blog post was created to celebrate World Migratory Bird Day (WMBD) 2023, a global event which increases the level of awareness about the threats that migratory birds are facing.

The theme of WMBD 2023 is Water, which highlights the importance of this resource for migrating birds – including for species like the Arctic Skua, which spends most of its life at sea and migrates thousands of kilometres over the ocean and across both hemispheres every year.

BTO’s Arctic Skua tracking project aims to understand where these birds spend their time when they’re not at their breeding colonies, so we can better inform global efforts to protect this species.

Discover more about Rousay’s Arctic Skuas and their astonishing migration in our other blog for WMBD 2023, written by BTO Senior Research Ecologist Nina O’Hanlon.

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Helen and David Aiton take us through their fieldwork seasons for BTO’s Arctic Skua tracking project.

1 October 2023

Where do Arctic Skuas go when they are not here?

For us, ‘here’ is Rousay, an island which lies off the West Mainland of Orkney. We have been measuring the breeding success of Arctic Skuas since 2014, and working with BTO to help track the adult birds’ migration since 2018.

13 Oct 2023

Scotland

How the BTO Acoustic Pipeline is helping to identify some of Europe’s most poorly-known bat species

WEBSITEEDITOR — Thu, 10 Aug 2023 09:36:25 +0000

A trip to a former Benedictine monastery provided our bat acoustics specialist with a unique opportunity to gather recordings of two cryptic bat species. No

Stuart Newson

Senior Research Ecologist

Stuart Newson is a Senior Research Ecologist in the Data Science and Bioacoustics team, where he is mainly involved in survey design and analyses of data from large national citizen science surveys.

Acoustic Pipeline

From the Nunnery to a Benedictine monastery

At the BTO Headquarters in Thetford, we are fortunate to have a roost of Brown Long-eared Bats in the Nunnery buildings where we work. Whilst a lot of research has been carried out on this species, particularly in western Europe, very little is known about the closely related Mediterranean Long-eared Bat.

It is often possible to identify bats by analysing recordings of their ultrasonic vocalisations. Although these sounds are at too high a frequency for most human ears to hear, specialist recording equipment is able to capture the calls for analysis. However, when it comes to the sound identification of the Mediterranean Long-eared Bat, the general thinking is that it cannot be distinguished from the Brown Long-eared Bat – and indeed, other closely related species – because their calls are too alike.

In June, I was given a unique opportunity: to spend a week working on Lokrum, a Croatian island near Dubrovnik, to collect sound recordings for the Mediterranean Long-eared Bat, and a similarly tricky species, David’s Myotis.

The BTO Acoustic Pipeline: our pioneering acoustic monitoring tool

The goal of the trip was broader than this, though. Funded by the Endangered Landscapes Programme (ELP), I was aiming to improve the capacity of BTO’s acoustic monitoring tool, the BTO Acoustic Pipeline.

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The former Benedictine monastery on Lokrum supports about 50 Mediterranean Long-eared Bats and 70 David’s Myotis, along with several other bat species of conservation interest. Photo by Chris Damant, Bernwood Ecology

The BTO Acoustic Pipeline is a powerful species identification tool, which analyses sound recordings and detects the wildlife found in them. It is the result of a decade of work by BTO, building machine-learning algorithms to automatically identify species from sound recordings – from birds and bats to small mammals and bush-crickets.

The focus on species identification means that the Pipeline is a valuable tool to support the ELP, which funds a suite of projects across Europe aiming to restore ecosystems and make them more resilient to environmental change. Being able to monitor how species respond to this environmental restoration work is key to evaluating how effective it is. However, species respond to change over large geographic areas and timescales, making this monitoring challenging.

Acoustic recording and analysis can be an excellent means of collecting and processing data at such large scales. Compared to traditional surveys, acoustic monitoring allows for continuous surveying over long periods with a much lower manual effort, coupled with a higher chance of detecting rarer, less vocal or less detectable species.

By improving the classifiers in the Pipeline – the algorithms which identify species from recordings – BTO can better support ELP’s ecosystem restoration projects in southern and eastern Europe where these two bat species, the Mediterranean Long-eared Bat and David’s Myotis, are found.

By improving the classifiers in the Pipeline – the algorithms which identify species from recordings – BTO can better support ELP’s ecosystem restoration projects in southern and eastern Europe.

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The Vincent Wildlife Trust’s knowledge of how Mediterranean Long-eared Bat and David’s Myotis (shown here) use the monastery was invaluable for targeting sound recording effort to collect the broadest possible range of calls. Photo by Henry Schofield

To do this, we need good-quality recordings for each of the target species, to train the machine-learning algorithms of the Pipeline to identify and distinguish them from recordings of other species.

Ensuring recordings are actually of the target species, and not of other similar species, is crucial for accurate algorithms. However, there are very few places in Europe where the Mediterranean Long-eared Bat or David’s Myotis can be recorded without also capturing calls of confusion species. The Mediterranean Long-eared Bat and David’s Myotis are not similar to each other, but rather, both have very similar relatives – the Grey Long-eared Bat and the Whiskered Bat respectively.

When I discovered that both these species had a roost in the monastery on Lokrum, I was very excited. These roosts were being studied as part of a project led by Henry Schofield, recent Head of Conservation at the Vincent Wildlife Trust (VWT). Visiting them gave me the rare opportunity to collect sound recordings for the Mediterranean Long-eared Bat and David’s Myotis in the absence of their confusion species.

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Spectrogram depicting short-duration calls of David’s Myotis.

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Spectrogram depicting long-duration calls of David’s Myotis.

What do bat sounds look like?

A major purpose of bat vocalisations is echolocation: the sound waves produced by the bat bounce off nearby objects in an echo which gives the bat information about its environment. For most bat species in Europe, the calls made by an individual bat change depending on the environment the bat is flying in, allowing the bat to collect the most relevant information about its surroundings.

In closed environments, like dense woodland or a confined roof space, bats produce very short calls which cover a broad band of frequencies (known informally as pitch). This type of echolocation call provides the bat with very detailed information about its close surroundings.

When the same bat flies into a more open environment, the band of frequencies covered by the calls is reduced, whilst calls become longer in duration. The echolocation now provides the bat with less detailed information, but that information covers a greater area.

Bat calls can be viewed on a type of chart called a spectrogram: a visual representation of a bioacoustic signal.

The different calls can be viewed on a type of chart called a spectrogram. This is a visual representation of a bioacoustic signal: a sound’s frequency on the vertical axis, amplitude (or volume) depicted as the intensity of colour, and how these change over time, along the horizontal axis.

The spectrograms here depict short- and long-duration calls of David’s Myotis. When comparing the two spectrograms, the greater range in frequency in short-duration calls is visible in the taller ‘lines’ of sound, and the length of long-duration calls is reflected in the greater width each sound occupies.

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Getting high-quality recordings inside a more confined roost setting can be particularly challenging. In this situation, we used tripods to ensure that we were still able to collect good recordings. Photo by Stuart Newson

Collecting recordings from the monastery

When I am recording bats around their roost sites, I need to apply this knowledge of different call types to make sure I capture, as far as possible, the complete range of calls that the bat species can produce. Normally, I would spend a couple of nights with a thermal camera, watching the bats leave and return to the roost to map their flight routes through different environments and identify areas where the bats produce the different types of vocalisations.

However, with the VWT’s knowledge of the roosts, there was already a lot of detailed information for me to start with. Working alongside VWT, I positioned our bat detectors carefully, choosing locations where we thought the bats would produce their full range of calls, from short- to long-duration echolocation calls as well as social calls.

I also had to be mindful of the immediate area around the recorders. Ideally, bat detectors or microphones should be at least 1.5 m up from the ground and away from any flat surfaces, including tree trunks and vegetation. Poorly placed recorders give us heavily distorted sounds, due to soundwaves refracting off these surfaces – these are difficult to identify or use for training algorithms. Fortunately, knowing how to avoid these problems, my recording efforts were successful!

Working together for bats

Thanks to the funding from the ELP, we were able to collect some high-quality recordings for both the Mediterranean Long-eared Bat and David’s Myotis. We’re now working with these recordings to update the BTO Acoustic Pipeline algorithms used for all European countries and regions where these species occur.

With the improved algorithms, and our new understanding of the sound identification of these species, we have a much better chance of identifying these species from acoustic recordings. In turn, this will make it possible for future ELP projects to monitor how their restoration activities might be helping these species recover in degraded habitats.

The ELP funding has enabled us to collect or collate recordings for six of the most cryptic bat species in Europe since our previous blog in October 2022, and dedicated recording collection work is only required for two more (excluding five island endemics). But these species, the Alpine Long-eared Bat and Anatolian Serotine Bat, remain two of the most challenging.

The work described in this blog was undertaken by Stuart Newson (BTO) in collaboration with a team from the Vincent Wildlife Trust, led by Henry Schofield. In addition to the help that VWT has provided, Stuart would also like to give particular thanks to Henry and to Chris Damant from Bernwood Ecology for the use of their photos here. The spectrograms shown here were produced in SonoBat.

This project was supported by the Endangered Landscapes Programme, managed by the Cambridge Conservation Initiative in partnership with Arcadia, a charitable fund of Lisbet Rausing and Peter Baldwin.

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BTO Acoustic Pipeline

From backyard sound projects to commercial bat surveys, the BTO Acoustic Pipeline provides tools for the detection and identification of birds, bats and other wildlife in both audible and ultrasonic sound recordings.

Accurate species identification and data management for acoustic monitoring, in conservation, management and site assessment.
For individual, commercial and large-scale use, with free and paid plans.

Learn more

1 August 2023 BTO and bats: solving cryptic puzzles BTO goes batty: how our Acoustic Pipeline project is contributing to bat conservation in some of Europe’s most threatened landscapesBTO Acoustic PipelineBailiwick Bat Survey 2022 Report

A trip to a former Benedictine monastery on Lokrum, a Croatian island near Dubrovnik, provided our bat acoustics specialist Stuart Newson with a unique opportunity: to gather recordings of two cryptic bat species, and develop the capacity of the BTO Acoustic Pipeline to identify them.

Mediterranean Long-eared Bats in the Abbots room of the monastery on Lokrum, Croatia. Photo by Chris Damant, Bernwood Ecology

10 Aug 2023 no

Science and our new strategy: why BTO is (and always has been) about more than counting birds

WEBSITEEDITOR — Wed, 26 Jul 2023 11:25:44 +0000

What does our new strategy mean for science at BTO? Director of Science James Pearce-Higgins explains why our data continue to play a crucial role in tackling the twin biodiversity and climate crises. No

James Pearce-Higgins

Director, Science

James is a member of the Senior Leadership Team at BTO. He is responsible for providing strategic leadership of the organisation’s science.

BirdTrackBreeding Bird SurveyGarden BirdWatchWoodcock SurveyBird Ringing SchemeHeronries CensusNest Record SchemeWaterways Breeding Bird SurveyWetland Bird SurveyNesting NeighboursCuckoo Tracking ProjectSeabird Monitoring ProgrammeGoose and Swan Monitoring Programme

Science

Staff voices

The difference we make

Now is an exciting time to be at BTO. At the start of July, we celebrated our 90th birthday with members and supporters, including some of our longest-serving volunteers. It is always a pleasure and a privilege to meet those who have been helping us monitor bird populations through decades of surveying, ringing, and nest recording.

Our 90th year has also seen the launch of an exciting new strategy for 2023–30. Our strategy focuses on maximising the impact of our science for birds, and growing the number and diversity of our supporters who will contribute to our science over the rest of this decade and beyond.

At the birthday celebration, I gave a talk which I subtitled ‘What is the point of the BTO?’ At the time of the twin global biodiversity and climate crises, what impact can a bird-focused NGO based in the UK really have? This is the question I want to consider in this blog, looking back at what we have already achieved, and looking forward to the impact we can have by 2030.

Looking back

The BTO monitoring schemes, many of which are supported through partnerships with JNCC, RSPB and other key environmental organisations, provide foundational information to support bird conservation in the UK. In combination, our schemes track changes in the abundance of around two-thirds of UK breeding bird species.

Our data contribute to official government statistics on the state of the environment, and underpin outputs such as The State of the UK’s Birds and the State of Nature Report. Ringing and nest monitoring data enable us to track changes in the survival and breeding success of more than 60 bird species, helping us to understand the causes of change.

For example, data gathered through the British and Irish Ringing Scheme showed us that crashes in England’s Lapwing population were mainly driven by low adult survival – the proportion of adults surviving each year. A run of cold winters reduced survival during the 1980s, and again in the winters of 2009/10 and 2010/11, decreasing the overall population size. The Nest Record Scheme then revealed a long-term decline in breeding success, which has meant the Lapwing population is not able to bounce back from the periods of low survival.

BTO scheme data revealed that crashes in England’s Lapwing populations were caused by low adult survival in cold winters. Population recovery was prevented by a long-term drop in breeding success, so the population continues to decline. © BTO

The value of counting birds

We are sometimes accused of simply monitoring species’ decline, focusing only on documenting the scale of biodiversity loss across the country. But these schemes also help us identify conservation solutions and track their effectiveness.

We are sometimes accused of simply monitoring species’ decline, focusing only on documenting the scale of biodiversity loss across the country. But these schemes also help us identify conservation solutions and track their effectiveness.

Our research into the declines of farmland bird species, identifying their causes and informing conservation solutions, is well known and continuing. We have documented the effects of climate change on biodiversity, and identified the species most vulnerable to future impacts, in order to inform conservation responses. And tracking of migratory birds such as the Cuckoo is helping to reveal the mysteries of migration to support the conservation of these declining species.

BirdTrack data are used by EuroBirdPortal’s mapping tool, to visualise birds’ migration across Europe in real-time.

The value of our monitoring schemes extends further still. Ringing has long been used to track the movements of marked birds, greatly increasing our understanding of migration. The recently launched Eurasian African Bird Migration Atlas makes this information available to scientists, policy-makers and the public, summarising ringing data from schemes across Britain and Europe for over 300 bird species.

BirdTrack provides an easy way for birdwatchers to submit sightings of birds and other wildlife, from anywhere, throughout the year. This information has always been valuable, contributing to our ability to track the migration of birds across Europe as it occurs. Amidst the current outbreak of avian influenza, however, easy reporting of bird mortalities through our award-winning app has enabled us to track the impact of the virus in real-time, as cases emerge. We report this information to governmental Statutory Nature Conservation Bodies and conservation NGOs on a weekly basis.

Looking forward: our new strategy

We want to build on these foundations to significantly expand our impact, so that the hard work of our volunteers and staff, and the funding that we receive, do even more for birds and for people. As part of our new strategy, we have identified four areas where our science will make a real difference in global attempts to address biodiversity loss.

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The BTO Acoustic Pipeline uses high-powered, algorithmic classifiers to identify wildlife from calls and song, like this Redwing flight call.

Charting change

Our long-term monitoring and demographic schemes remain foundational to UK bird conservation. In an increasingly devolved world, we want our data to highlight environmental change and track responses to policy interventions equally well across all nations of the UK.

We also want to improve coverage across different habitats, to make sure data collected through the schemes are representative of the UK’s diverse environments. Whilst continuing to grow our existing schemes, this will also provide opportunities to help us collect data from new places, like our Upland Rovers scheme (part of the BTO/JNCC/RSPB Breeding Bird Survey) or in new ways, such as for the BTO Acoustic Pipeline.

Our new strategy gives us the opportunity to grow our monitoring surveys, such as the Upland Rovers scheme.

BirdFacts provides information and trend data for all UK bird species.

Delivering data

We need the data from our schemes to work harder to have maximum impact. This year, we made the information and trend data that these schemes produce more engaging and accessible through a relaunched BirdFacts, and the new Birds on your Doorstep data explorer – check them out if you haven’t seen them!

Building on this, we will continue to provide more local information about birds in your area. We are also keen to support landowners and conservation organisations who use our data, helping them identify the most important places for birds and to monitor the success of conservation on a landscape scale. Similarly, we will expand our Data Reports to make the best information available for Ecological Impact Assessments.

We’re also working in partnership with more organisations, to share our data, knowledge and expertise as widely as we can. For example, we recently joined Wildlife and Countryside Link, the largest environment and wildlife coalition in England.

Our research on offshore renewables is identifying the risks of wind farm development to birds and developing mitigation solutions.

Seeking solutions

We will continue to undertake cutting-edge research to develop and test conservation solutions, and to monitor their effectiveness.

Our recent high-impact work on protected sites shows the potential for our large-scale and long-term data to do this. In the context of the climate crisis, our research on offshore renewables is identifying the risks of wind farm development to birds, developing mitigation solutions, and reducing the conflict between renewable energy production and bird conservation.

Similarly, by working closely with NatureScot, Natural England and the forestry industry, BTO has developed maps which identify areas of the UK with the highest concentrations of breeding waders. These will inform plans for large-scale tree planting – part of this country’s progress towards its Net Zero climate goals – to ensure they do not conflict with the conservation of threatened and declining species such as Curlew.

Our research will inform plans for large-scale tree planting, to ensure they do not conflict with the conservation of threatened species such as Curlew.

Framing futures

Avian influenza research will be a key area of work over the next few years, as we identify the species and populations that have been most impacted by the outbreak.

We know that the world is changing rapidly. This means we need to be able to identify and tackle threats to birds as they emerge.

The most current of these threats is avian influenza. BTO has been working hard with partners to track the impacts of this virus and inform responses to the outbreak. This will be a key area of work over the next few years as we identify the species and populations that have been most impacted by the outbreak, providing data to inform their conservation, and for future risk assessments.

We will also continue to track and report on the impacts of climate change on birds. Increasingly, we will inform climate change adaptation to support species’ conservation in a changing climate, and to track the success of those interventions.

What next?

I hope I have provided a snapshot of the importance of our work and shown that there is indeed a point to BTO!

If you are one of our supporters and volunteers, thank you. I hope this blog has helped you see the difference your contribution has made, and that you are enthused as I am to continue to support BTO and help us have even more impact for birds and for people.

If you do not currently support BTO, please consider doing so either financially or through our surveys. And if you are a professional and would like to work with us to help us achieve these goals, then please do also get in touch.

Our work depends on people like you

Each year we need to raise thousands of pounds to fund our research and provide crucial evidence for the conservation of bird species and habitats.

Support our science with a donation.

Donate

Our research would not be possible without our extraordinary volunteers, who gave 2,029,493 hours to BTO work in 2021.

Join our community and support our research through our volunteer projects, from as little as 15 minutes a week.

Volunteer

2 July 2023

Cathy Ryden / BTO

Senior Leadership Team

28 Jul 2023

Flight Paths: the story of bird migration science

WEBSITEEDITOR — Fri, 07 Jul 2023 15:00:46 +0000

Science writer Rebecca Heisman tells us how she came to write her first book, Flight Paths, and why it’s vital that we tell the stories of the birds around us.

Rebecca Heisman Science writer Visit Rebecca’s website Rebecca has written for many leading ornithological organisations including the Audubon Society, the Cornell Lab of Ornithology and the American Ornithological Society. Her first book, Flight Paths, was published in 2023 by Swift Press.

During that initial round of COVID-19 lockdowns, people all over the world were searching for a way to keep themselves occupied at home, and began to take fresh notice of the birds in their neighbourhoods. I was one of them – though I was already a casual birder, I found particular solace in the return of migrating birds that spring. They were a reminder of hope and continuity beyond the personal and professional turmoil I was experiencing.

Before COVID-19, I worked full-time as a communications staffer for the American Ornithological Society, the world’s largest professional organisation for bird scientists. A large part of my job was reading scientific studies being published in their journals and promoting them to journalists and the public. I read a lot of papers and talked to a lot of researchers, and I was fascinated by the methods used in many of the studies. I was amazed that you could study bird migration using weather radar, for example, by analysing hydrogen isotopes in feathers, or by recording the calls of birds passing overhead.

By the summer of 2020, I had left that job, overwhelmed by the demands of pandemic childcare and a serious medical diagnosis of my own. But my fascination with how we know what we know about migrating birds stuck with me, and I began to write a book proposal in hopes of exploring the subject further.

Never having written a book before, I found myself figuring out the process as I went. There were definitely some surprises along the way. Yes, I got to join ornithologists in the field as they did their work, tagging along as they snuck up on nesting Long-billed Curlews on the Montana prairie, or attempted to recapture Swainson’s Warblers carrying tracking devices as they returned to the swamps of Louisiana. But I also talked to experts from a range of other disciplines that I didn’t necessarily expect – computer scientists, electrical engineers, geochemists, and at one point even a philosopher.

A researcher removes a tracking device from a Swainson’s Warbler as part of a migration study. Rebecca Heisman

The study of bird migration, it turns out, has drawn from almost every branch of science. The use of weather radar to study ornithology had its origins in the earliest days of military radar usage in World War II. Early attempts to track birds using radio transmitters were made possible by the invention of the transistor and inspired by the launch of Sputnik. Researchers who study nocturnal flight calls rely on artificial intelligence to help identify and categorise the calls in their recordings. Efforts to determine birds’ geographic origins using their DNA, a sort of 23andMe for birds, were spurred by the advances of the Human Genome Project. I found myself joking that what I was really writing was writing a comprehensive history of the technological advancements of the 20th century, as told through the history of bird migration research.

Of course, my challenge was to distil this highly technical information into a book that would be engaging and hopefully even entertaining to read, regardless of whether someone had a background in the sciences. Ultimately, what draws people in are stories, not facts and figures, and the scientists I spoke with were generous in sharing their stories with me.

Ultimately, what draws people in are stories.

I talked to an ornithologist in Mongolia whose interest in birds was sparked by participating in a young naturalists’ club run by the Soviets when he was a child and his country was part of the USSR; a scientist in the USA who recalled struggling to string grants together to fund her research into bird genetics while also dealing with the demands of young motherhood; and a researcher who was astonished when a thrush she’d fitted with a radio transmitter in her home country of Colombia was then detected by a receiver only 200 km from the university campus in Canada where she was studying for her graduate degree. BTO’s own Nigel Clark spoke with me about his experiences tracking critically endangered Spoon-billed Sandpipers via satellite, packing three precious miniature transmitters on a flight to Asia in 2016 to try and uncover the details of their migratory routes and improve biologists’ chances of saving the species.

Stable isotope analysis examines the atoms in feathers to determine the geographic areas inhabited by the bird when the feathers were grown. It has been used in BTO research on several species, including Shelduck. Philip Croft / BTO

Sometimes, though, I had to get pretty creative to find a story in the science. The chapter of Flight Paths that covers stable isotope analysis opens with the sentence “Imagine you’re a deuterium atom,” cheekily inviting the reader along on the atom’s journey from the ocean into a raincloud and from there into a tree, a caterpillar, and finally, the feather of a Prothonotary Warbler.

One of the most satisfying chapters to write was the one that covered ‘citizen’ or ‘community’ science – the ways in which everyday birders who aren’t scientists in their day jobs can make real contributions to our understanding of migration. Birders who record their observations and submit them to databases such as BirdTrack aren’t just keeping busy. They’re adding to a massive dataset that scientists are using to drill down with incredible detail into where on the globe any given species is most likely to turn up on any day of the year.

Today, efforts like these are more crucial than ever before, because migratory birds are in trouble. Populations are in decline around the world. A recent analysis of North America’s birdlife found that there are around three billion fewer birds living on the continent today than there were in 1970. Similarly, BTO has calculated that the number of birds in the UK has decreased by 73 million in the same time period (a startling number when you consider that the UK is approximately 100 times smaller than North America in land mass), and that up to 46% of the regularly occurring bird species are in danger of being lost.

I hope that everyone who reads Flight Paths comes away with a feeling of optimism that it’s still possible to tackle the environmental challenges facing us.

Insights into the migration of species such as the Cuckoo have been revealed by BTO research. Neil Calbrade / BTO

In order to effectively target conservation efforts, we need detailed data on the breeding ranges, wintering ranges, migratory routes, and stopover sites used not just by species but by the individual populations that make up those species (a concept known as ‘migratory connectivity’) – but for many birds, this information is still not available. So migration research, from the very high-tech to the simple submitting of checklists by amateur birders, is continuing with new urgency.

I hope that everyone who reads Flight Paths comes away with a new appreciation of the hard work and creativity that went into uncovering every impressive fact we know about bird migration, and with a feeling of optimism that it’s still possible to tackle the environmental challenges facing us.

During the early days of COVID-19, birds were a source of hope for me, and for millions of others. Now it’s our turn to be a source of hope for them.

flight-paths-rebecca-heisman-uk-cover.jpg

Flight Paths: How the Mystery of Bird Migration Was Solved

“This fascinating book opens with a question: where do the birds go? People have, of course, been asking this question for centuries...the book does not answer this question directly but delves into the question of how we know where birds go.”

Rebecca’s first book, Flight Paths, tells the story of the study of bird migration, from ringing and radio-tagging to cross-continent citizen science projects.

BTO’s Associate Director of Research Rob Robinson lends his expertise to our book review.

Read the review

Science writer Rebecca Heisman tells us how she came to write her first book, and why it’s vital that we tell the stories of the birds around us.

July 2023

The idea that became Flight Paths, my first book, was born in the spring of 2020.

07 Jul 2023 no

Cuckoos’ clocks can’t adjust to climate change – now we know why

WEBSITEEDITOR — Wed, 21 Jun 2023 14:46:17 +0000

Why aren’t Cuckoos returning any earlier as spring advances, and why is this important? No

Chris Hewson

Senior Research Ecologist

Chris is a Senior Research Ecologist in the Framing Futures Team where he works on the status, ecology and conservation of Afro-Palaearctic migratory birds and of forest birds across the world.

Projects primarily focus on improving knowledge of the migration ecology of these species, with the aim of understanding the drivers of recent population changes and the likely population impacts of projected environmental change, with the ultimate aim of facilitating restoration of flyways and populations.

Cuckoo Tracking Project

Science

Staff voices

The difference we make

UK springs are starting earlier as the climate warms, with bud burst and the emergence of invertebrates such as caterpillars that eat this young vegetation happening earlier too. These invertebrates are a vital and ephemeral food source for breeding birds, so migratory species that have not advanced their migrations and subsequent breeding accordingly risk missing out.

One species that has not significantly shifted the timing of its spring migration forward is the Cuckoo, the iconic harbinger of spring. Previous BTO work has shown that the advance in the Cuckoo’s arrival has been smaller than that of many other species, and it has undergone a substantial population decline, in England especially.

In general, both migratory and resident species that have not advanced their breeding have undergone greater population declines than others, but there’s been limited evidence linking this to a reduction in breeding success in these species. This suggests that other demographic pathways, such as adult survival, may be important. Understanding why some migratory species have not advanced their arrival, and what the consequences of this are outside of the breeding season, is therefore vital for understanding population declines and helping us work out the best ways to help.

Investigating the drivers of the Cuckoo’s migratory schedule

Satellite-tagged Cuckoo. Mike Toms / BTO

Using data from 87 adult male Cuckoos tagged as part of BTO’s Cuckoo Tracking Project, we looked at which events across their annual migratory schedule were most important in determining when birds arrived back to the breeding grounds. We also looked at whether migratory timing affected mortality risk at different migratory stages. And to help us understand variation in timing across the annual cycle, we examined whether timing was consistent between individuals.

We found that the timing of departure from the pre-Sahara crossing stopover in West Africa in spring is the most important factor in determining when Cuckoos arrive back to the UK. Furthermore, both the high level of synchrony across the population at this stage and relatively modest levels of consistent timing differences between individuals suggest that environmental conditions constrain when birds can depart from this stopover.

Our tracking work has revealed that Cuckoos use this stopover in March and April each year. In this part of Africa, rains arrive at this time every year, moving up from the southern hemisphere in association with a system known as the Intertropical Convergence Zone. These rains bring about a flush of invertebrate prey, which migratory species such as the Cuckoo rely on to fuel their northward journeys. This study is the first to find that departure from a stopover site limits a land bird species’ arrival to its breeding grounds across multiple years.

In addition to departure from West Africa, we found that spring arrival on the breeding grounds was determined to lesser, but important, extent by migration speed during the northward journey across Europe, as well as the timing of Cuckoos’ arrival south of the Sahara the previous autumn. The latter is surprising given that earlier research has shown timing differences between individuals are largely reset during the winter period – there is usually only a limited carry-over effect of timing from autumn to spring migration.

Why can’t Cuckoos change their clocks?

Previous research looking at patterns across many species has shown that, in general, the timing of departure from the wintering grounds is the major determinant of variation in when migratory birds arrive back to their breeding sites. The timing of this departure also has a higher level of consistent differences between individuals than other events. This indicates a greater direct control by internal migration programmes. Hence, an advance in the timing of departure from wintering sites provides a potential evolutionary mechanism via which spring arrival at breeding grounds can also be advanced.

Our results show, however, that this is not an option for UK Cuckoos. The timing of their departure from their wintering grounds in the Congo rainforest zone has little effect on when they arrive back to their breeding sites; in fact, all other things being equal, birds that depart their wintering grounds later arrive back a little earlier.

These results help us to understand both why the phenological response (the timing of annual cycle events) to climate change is so limited in some species, and why migratory species which travel further are less likely to be able to advance their spring arrival timing than ones that make shorter journeys. Similar results might be found for some other very long-distance migrants which, like the Cuckoo, migrate to the southern hemisphere for the midwinter period and rely on stopovers in the northern tropics to prepare for crossing the Sahara in spring. Overall, the seasonality of sites used across the annual cycle is likely to be more important than their position in the annual cycle in determining their relationship to breeding grounds arrival and the potential for its advance.

Why is it important to understand what drives birds’ migratory behaviour?

Cuckoos which arrive earlier in the UK to establish the best territories risk a higher level of mortality. Edmund Fellowes / BTO

By looking at how mortality risk varied with timing across the annual cycle, we were able to gain some important insights into how these limitations to migratory change can impact individual birds, and therefore potentially populations.

In periods following the migration stages that were most important in determining the timing of arrival on breeding grounds, early birds were more likely to die than later ones. This suggests that, to try to gain the benefits of early breeding grounds arrival, such as claiming the best breeding territories, birds suffer increased mortality risk. In other words, there is a trade-off between survival and the benefits of early arrival, perhaps due to birds migrating with less on-board fuel than they otherwise would. Such risks may become more necessary as birds try to keep up with climate change on the breeding grounds.

The fact that we found that migration timing didn’t reset during the midwinter period, and that part of post-breeding migration is included in the periods when birds appear to be exposing themselves to these risks, suggests that in the case of UK Cuckoos, all ecological levers are being pulled in an attempt to advance spring arrival. The resulting increased mortality may form part of the demographic mechanisms linking failure to advance spring arrival to population declines.

Using our research to help birds adapt to global change

Providing higher quality habitat at breeding grounds like Wheatfen, Norfolk will support Cuckoos. Phil Atkinson / BTO

Not only do these results help in understanding why some species are not keeping pace with ever earlier springs and advancing their arrival to the breeding grounds, and how this might impact their populations, it also helps to show how we might help these birds cope better with the demands of global change.

We can identify pinch points in the annual cycle that impact spring arrival, and where early birds are at increased risk of mortality. The stresses these birds are under can potentially be alleviated by improving habitat quality at stopovers, to increase fattening rates and reduce costly trade-offs between survival and reproduction. The most important places to concentrate flyway restoration efforts are the stopovers used in spring and autumn to prepare for the Sahara crossings and, to lesser extent, the areas used to recover from the Sahara crossings and migration across Europe in spring.

As we also found that birds that were late leaving the breeding grounds were at greater risk of dying than those leaving earlier, suggesting they are energetically limited at this point, provision of better-quality habitat on the breeding grounds is also a priority.

Cuckoos in our past and in our future

These results shed light on one of the oldest mysteries in folklore – what determines when Cuckoos arrive back at their breeding sites, and whether they really are a sign that spring is here...Ultimately, they could help us reverse the Cuckoo’s population decline in the UK.

These results shed light on one of the oldest mysteries in folklore – what determines when Cuckoos arrive back at their breeding sites and whether they really are a sign that spring is here. These results show that in fact, events occurring more than three thousand miles away are more important in determining overall variation in Cuckoo arrival back to the UK than events closer to home. But when focusing specifically on whether individual birds are early or late relative to their own schedule in different years, it seems that conditions in Europe are much more important. So, as Cuckoos are very faithful to their breeding sites, the old adage that Cuckoos are a sign that spring is on the way may well contain some truth from a local perspective after all.

In our future work, we will need to assess exactly how the departure of Cuckoos from critical stopover sites is impacted by the combination of climatic and habitat factors birds experience. This will give us a better idea of how each currently contributes to the timing and success of migrations, and how best we might use habitat restoration to help birds improve migratory performance, and ultimately, reverse their population declines in the UK.

2 June 2023 Can Cuckoos adapt their clocks to climate change?

Several studies from BTO and elsewhere have revealed alarming declines in species that breed in the UK and spend our winter months in Africa. However, these declines are less severe in migratory species that have adjusted the timing of their arrival back to their UK breeding grounds to keep pace with ever earlier northern hemisphere springs. But one species that has not significantly shifted the timing of its spring migration forward is the Cuckoo, the iconic harbinger of spring.

21 Jun 2023 no

Finding food: deciphering the foraging ‘fingerprints’ of Gannets

WEBSITEEDITOR — Wed, 05 Apr 2023 10:03:49 +0000

Chris Pollock explains how studying the unique movements and behaviours of individual Gannets can help us to understand the impact of environmental change on their populations. No

Chris Pollock

Chris Pollock Quantitative Ecologist at the UK Centre for Hydrology and Ecology (CEH) Chris recently joined UK CEH after working for BTO as a Research Ecologist, investigating the impacts of offshore renewable energy on seabirds. He loves ecological modelling and wants to share its role in conservation with the wider world.

Guest voices

Science

Gannet

The first use of remote satellite tracking for seabirds in 1989 revolutionised our understanding of their behaviour. Since then, there has been an explosion in the number of studies that track the movements and migration of a multitude of species.

There is a lot about seabirds that we still don’t know, however. Seabird ecologists like me are still trying to understand why the species they study occupy certain spaces and behave in certain ways. To this end, we are often tempted to grab as many fancy new tracking devices as our budget can afford and head to the nearest coastline in search of some unsuspecting birds.

These devices provide us with lots of information about the location and movements of the birds, which we can then analyse to see if differences in behaviours – such as time spent resting, foraging and travelling – might be due to differences in sex (male or female birds), age (immature or adult birds) or even the breeding colony location.

These methods have given us great insight into seabird behaviour. But more and more studies are highlighting the importance of understanding the movements and behaviours of individual birds. You could think of this as trying to understand a single bird’s personality.

Introducing the foraging ‘fingerprint’

Individual Gannets leave their breeding colony in the same direction on each foraging trip, search for food in the same area on successive trips, and will even return to that spot from year to year.

One prominent example of this is called ‘individual foraging site fidelity’ (IFSF), which describes a pattern of behaviour well documented in Gannets. Tracking devices have revealed that individual Gannets leave their breeding colony in the same direction on each foraging trip, search for food in the same area on successive trips, and will even return to that spot from year to year.

You can think of the foraging patterns which have been revealed by tracking as a Gannet’s foraging ‘fingerprint’ – a pattern unique to that bird.

Gannets foraging in the Firth of Forth, Scotland. Chris Pollock

Why might a Gannet want to return to the same spot again and again?

Well, Gannets breed in large colonies – the largest in the world is located on Bass Rock, Scotland, and is made up of around 150,000 breeding adults! When foraging from such a big colony, it makes sense to remember an area where you have had a successful foraging trip. There will be a lot of competition for fish from other Gannets, so making your trip as efficient as possible will be beneficial to you and the hungry chick you have to feed back at the colony.

The next question that we must ask ourselves is what processes underpin this foraging fingerprint. For example, Gannets might use memory to recall particularly rich foraging sites, or observe other Gannets to see where they feed successfully, and copy them.

To investigate this question with more tracking devices, we would need to track all the Gannets from a colony at once to understand social interactions. This would be incredibly expensive, not to mention the practical impossibility of attaching 150,000 tags to adult Gannets. And as of yet there are no questionnaire techniques to interrogate Gannets about how they repeatedly find their favourite feeding spots.

This is where simulation models come into play.

Simulation models allow us to investigate the underlying mechanical processes in natural systems. When we create a model, we can construct a scenario and then apply different ‘rules’ for how an organism might interact with others and its environment. Then we can see which rules generate the result closest to that which we see in real life, and are therefore likely to reflect the mechanisms underpinning that reality.

Deciphering the fingerprint

gannet_foraging_gif.gif

This simulation depicts individual Gannet foraging trips, each departing from the Bass Rock colony in the Firth of Forth, Scotland. Outward trips (yellow) include foraging behaviour (red). The birds return to the colony (blue) after foraging.

My quintessential lightbulb moment occurred during my PhD when reading about a tracking study which suggested that Gannets anticipate their prey location. The study stated that “further investigations are necessary to identify the mechanisms involved in seabird resource localisation, such as sensorial abilities, memory effects, public information [another term for social interactions] or a combination of these factors”.

I’d already begun to work with simulation models, and it dawned on me that they would provide the perfect format to do exactly that. By modelling scenarios with different rules for memory use, the impact of social interaction and combinations of these, I could investigate the factors which determined a Gannet’s individual foraging fingerprint – the departure direction and foraging area used in repeated feeding trips.

I could then see which models produce the best ‘fit’ for the fingerprint that has been revealed by tracking, gaining insight into what Gannets think and how they interact with each other.

I began by hypothesising a range of rules which might govern Gannet foraging behaviour. They incorporated the use of memory (e.g. short or long-term), and how Gannets interacted with each other while on foraging trips (e.g. attraction to others foraging, or avoidance of areas with high concentrations of other Gannets).

In total, I constructed 16 different rules or rule combinations based on memory and social interaction, with varying levels of complexity. Then I ran my simulations of Gannet behaviour governed by each of my hypothesised rules or rule combinations, and analysed the results from a few random individuals in each simulation – like sampling from a real-life population. The results were fascinating.

The simulation which produced the most realistic movements of individual Gannets was governed by both memory and social interaction – the most complex rule combination that we created.

The simulation which produced the most realistic movements of individual Gannets was governed by both memory – remembering several different locations to visit – and social interaction – using other Gannets as cues for where food might be located and as indicators of very high competition. This rule combination was the most complex that we created.

I would argue that this is interesting in and of itself, but what are the potential real-world applications for such a study?

Modelling in the real world

What are the impacts of offshore wind farms on our seabirds? Modelling research is helping to uncover the details. Tommy Holden / BTO

With this information about the mechanisms which govern seabird foraging behaviour, we have a more robust baseline for further research. We can create new models founded on this baseline to investigate how changes to the environment might affect our seabirds.

One of the most prominent potential threats to Gannets and other seabirds from UK colonies is the rapid development of offshore wind farms around our coasts. With government plans to more than triple our capacity within the next 10 years, we must do our best to predict the potential impacts of different development plans on the distributions and population sizes of our treasured seabirds – and modelling can help.

‘Collision risk modelling’ is a type of simulation modelling which investigates the risk of seabirds flying into wind turbines. It is often used to inform the Environmental Impact Assessments conducted for potential developments, for example.

More recently developed models are examining how offshore wind farms might disrupt seabird foraging trips. So far, the modelling techniques we have indicate that the cumulative effects of offshore wind farm development are having an impact on our seabirds.

Looking ahead

We now have the potential to simulate these ‘bird brains’ (historically an insult, although I would say one which is rapidly being disproved) as they learn and memorise things and react to competitors in a myriad of ways. Our simulations are representative of reality and of our ever-increasing knowledge of the complexities of these birds. I look forward to applications looking at immediate threats such as wind farms and changing prey distributions to predict how our feathered friends may fare in these challenging times.

This blog is based on the research and findings of Chris's PhD, Modelling breeding season foraging and tracking autumn migrations to fill knowledge gaps in gannet ecology relating to impacts of offshore wind farms (University of Leeds, 2022).

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