BTO - British Trust for Ornithology - Species interactions

A niche-based approach for evaluating the mechanisms of community stability in butterfly communities across three countries

MIKETOMS — Wed, 22 Mar 2023 09:34:18 +0000

The Cuckoo cohort of 2024 takes flight!

Evans, L.C., Melero, Y., Schmucki, S., Boersch-Supan, P.H., Brotons, L., Fontaine, C., Jiguet, F., Kuussaari, M., Massimino, D., Robinson, R.A., Roy, D.B., Schweiger, O., Settele, J., Stefanescu, C., van Turnhout, C.A.M. & Oliver, T.H. Global Change Biology 10.1111/gcb.16684 At large scales, the mechanisms underpinning community stability in natural populations may vary in importance due to changes in species composition, mean abundance, and species richness. Here we link species characteristics (niche positions) and community characteristics (richness and abundance) to evaluate the importance of stability mechanisms in 140 butterfly communities across three European countries and spanning five bioclimatic regions. We construct niche-based hierarchical structural Bayesian models to explain first differences in abundance, population stability, and species richness between the countries, and then explore how these factors directly and indirectly (via synchrony and population stability) impact community stability. Species richness was partially explained by the position of a site relative to the niches of the species pool, and species near the centre of their niche had higher average population stability. The differences in mean abundance, population stability, and species richness then influenced how much variation in community stability they explained across the countries. We found, using variance partitioning, that community stability in Finnish communities was most influenced by community abundance, whereas this was unimportant in Spain with species synchrony explaining most variation; the UK was somewhat intermediate with both factors explaining variation. Across all countries, the diversity-stability relationship was indirect with species richness decreasing synchrony which increased community stability, with no direct effects of species richness. Our results suggest that in natural communities, biogeographic variation in key drivers of stability, such as population abundance and species richness, lead to community stability being limited by different factors and that this can partially be explained due to the niche characteristics of the European butterfly assemblage. We thank the volunteers collecting butterfly data and the funders of the schemes for the obtaining the data required for this study. The UK Butterfly Monitoring Scheme is organized and funded by Butterfly Conservation, the Centre for Ecology and Hydrology, British Trust for Ornithology, and the Joint Nature Conservation Committee. The Catalan BMS is funded by the Catalan Government, the Barcelona Provincial Council and other local partners. The Catalan BMS also incorporates the Andorra BMS that is run by CENMA and funded by Govern d'Andorra. The Finnish BMS is organized and funded by the Finnish Environment Institute (SYKE) and the Finnish Ministry of Environment.

Nest survival of threatened Eurasian Curlew (Numenius arquata) breeding at low densities across a human-modified landscape

VIOLA.ROSS-SMITH — Sat, 24 Dec 2022 19:50:25 +0000

The Cuckoo cohort of 2024 takes flight!

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Ewing, H., Franks, S., Smart, J., Burton, N. & Gill, J.A. Ibis 10.1111/ibi.13180

Targeted management actions to boost key demographic rates can help to restore rare and localised populations but are increasingly required to stabilise or reverse declines of formerly common and widespread species. Many breeding wader populations across Europe are declining because of unsustainably low rates of productivity, and the conservation tools designed to boost wader breeding productivity have been most effectively used for semi-colonial species within protected areas.

Targeted management for wader species that breed at low densities across human-modified landscapes, such as the rapidly declining Eurasian Curlew Numenius arquata, is likely to be more challenging. Here, we quantify variation in curlew nest survival in order to explore how management could be targeted to boost this key component of breeding productivity. Up to 80 pairs of Eurasian Curlew were monitored annually between 2019 and 2021 in eight locations across Breckland, eastern England, where nesting densities range from < 1 to ca.7 pairs per km-2.

For 136 nests across grassland- and arable-dominated sites, the majority of failure (86%) was caused by (primarily nocturnal) predation and the mean probability of surviving incubation (PSI) for all hatched or predated nests (127) was ca. 0.25. Nest survival showed little annual or seasonal variation but did vary slightly between sites, however, this spatial variation was not clearly related to management conditions or nest concealment at these sites.

Fencing to exclude mammalian nest predators can be effective for waders, but too few Eurasian Curlews currently nest within fenced areas in Breckland to produce observable effects. Fencing the few sites with high nesting densities could potentially double the number of chicks hatched each year within the study area, but landscape-scale actions to reduce predator impacts on nests and chicks are likely to be needed to maintain breeding numbers in the wider countryside.

The authors are extremely grateful to the land-owners and managers who granted permission for this research to be conducted on their land, as well as to the many supportive farmers, gamekeepers, graziers, conservationists and members of the Breckland community for their help monitoring nesting curlew throughout this project.

Long-term trends of second generation anticoagulant rodenticides (SGARs) show widespread contamination of a bird-eating predator, the Eurasian Sparrowhawk (Accipiter nisus) in Britain

VIOLA.ROSS-SMITH — Tue, 04 Oct 2022 09:56:05 +0000

The Cuckoo cohort of 2024 takes flight!

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Broughton, R.K., Searle, K.R., Walker, L.A., Potter, E.D., Glória Pereira, M., Carter, H., Sleep, D., Noble, D.G., Butler, A. & Johnson, A.C. Environmental Pollution 10.1016/j.envpol.2022.120269 Second generation anticoagulant rodenticides (SGARs) are widely used to control rodents around the world. However, contamination by SGARs is detectable in many non-target species, particularly carnivorous mammals or birds-of-prey that hunt or scavenge on poisoned rodents. The SGAR trophic transfer pathway via rodents and their predators/scavengers appears widespread, but little is known of other pathways of SGAR contamination in non-target wildlife. This is despite the detection of SGARs in predators that do not eat rodents, such as specialist bird-eating hawks. We used a Bayesian modelling framework to examine the extent and spatio-temporal trends of SGAR contamination in the livers of 259 Eurasian Sparrowhawks, a specialist bird-eating raptor, in regions of Britain during 1995–2015. SGARs, predominantly difenacoum, were detected in 81% of birds, with highest concentrations in males and adults. SGAR concentrations in birds were lowest in Scotland and higher or increasing in other regions of Britain, which had a greater arable or urban land cover where SGARs may be widely deployed for rodent control. However, there was no overall trend for Britain, and 97% of SGAR residues in Eurasian Sparrowhawks were below 100 ng/g (wet weight), which is a potential threshold for lethal effects. The results have potential implications for the population decline of Eurasian Sparrowhawks in Britain. Fundamentally, the results indicate an extensive and persistent contamination of the avian trophic transfer pathway on a national scale, where bird-eating raptors and, by extension, their prey appear to be widely exposed to SGARs. Consequently, these findings have implications for wildlife contamination worldwide, wherever these common rodenticides are deployed, as widespread exposure of non-target species can apparently occur via multiple trophic transfer pathways involving birds as well as rodents. The authors are grateful to funding from NERC grant NE/S000100/1 and thank the public for submitting specimens to the PBMS, which is supported by the Natural Environment Research Council award number NE/R016429/1 as part of the UK-SCAPE program delivering National Capability. The PBMS is additionally funded by Natural England and the Campaign for Responsible Rodenticide Use (CRRU). The BTO/JNCC/RSPB Breeding Bird Survey is a partnership jointly funded by the BTO, RSPB and JNCC, with fieldwork conducted by volunteers. The authors thank Stephen N Freeman, and are particularly grateful to the late Professor Richard Shore, who instigated this work.

Breeding bird population trends during 2013–2019 inside and outside of European Badger control areas in England

MIKETOMS — Fri, 19 Aug 2022 14:21:41 +0000

The Cuckoo cohort of 2024 takes flight!

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Ward, C.V., Heydon, M., Lakin, I., Sullivan, A.J. & Siriwardena, G.M. Journal of Zoology 10.1111/jzo.13010 Since 2013, the Department for Environment, Food and Rural Affairs (Defra) has licenced culling of European Badger (Meles meles) populations in several English regions. In the first 7 years, more than 100 000 Badgers have been removed. It is critical to evaluate the ecological impact of severely depressing the population of a widespread predator from large areas of the country, such as effects on breeding bird populations. Citizen science survey data on the abundance of breeding birds supports the estimation of population trends, i.e. whether species are exhibiting population growth or declines, and the effects of potential environmental influences, such as Badger removal, on these trends. Here, these survey data are used together with data on the presence and amount of culling in an area to explore whether removing Badgers has an effect on breeding bird populations both inside and outside culling zones from 2013–2019. This is not equivalent to a controlled trial, but collects critical, landscape-scale evidence in real-world conditions. In analyses evaluating the effect of culling presence, 18 of 55 bird species showed significant or near-significant growth rate changes. Of these, four species had higher growth rates and 14 exhibited lower growth rates in cull areas, compared to areas outside of the culling zones. When using culling intensity data to assess the impact on growth rates, 10 of 55 species showed significant or near-significant results, with only one species exhibiting a higher population growth rate in the presence of more intensive culling. Predicted sensitivity to Badger effects based on species’ ecologies did not predict whether the measured relationships were significant, or their directions, suggesting that other factors underlie the patterns seen. Hence, there was little evidence to indicate consistent, community-level effects of Badger removal on bird populations. Reasons why this predator removal has not affected bird populations are discussed.

We are grateful to Esther Kettel for her input to method development. This study was funded by Natural England, whose spatial data and analysis team we thank for their help on this project. Three anonymous reviewers helped to improve the manuscript. The BBS relies on thousands of volunteer surveyors and regional organizers, and we are indebted to them for making this study possible. The BBS is funded by a partnership of BTO, the Joint Nature Conservation Committee (JNCC) and the Royal Society for the Protection of Birds (RSPB).

A comparison of breeding bird populations inside and outside of European Badger <em>Meles meles</em> control areasThe Breeding Bird Survey 2021The Breeding Bird Survey 2020

Since 2013, the Department for Environment, Food and Rural Affairs (Defra) has licensed culling of Badger populations in several English regions. This programme is part of a government policy response to Bovine Tuberculosis, a disease that has major implications for the British cattle farming industry. Between 2013 and 2019, over 100,000 Badgers were culled.

It is important to evaluate the ecological impact of severely depressing the population of a widespread predator within large areas of the country. Badgers have a varied diet that includes earthworms, slugs, fruits, small mammals and birds, the latter mostly comprising eggs or chicks in nests located on or close to the ground. Levels of predation on the nests of birds could be directly affected by the removal of Badgers, or indirectly affected by population responses of other predators following their release from competition with Badgers. In turn, it is then possible (but by no means certain) that Badger removal will affect bird population trends.

By examining population growth rates of both ground-nesting and non-ground-nesting breeding birds, inside and outside of cull areas, this study set out to assess possible effects of Badger removal on bird populations. The study extends the work of Kettel et al. (2021), using data from two additional culling years, further regions under culling treatment and a measure of local cull intensity, all of which should increase the power of the study to identify possible effects.

The new study was able to set a minimum sample size that is double that used previously, which increases the robustness of the approach. This study provides an important further assessment of a high-profile policy initiative, using the best data that are available. As before, the study design was limited by the geographical pattern in which culling has been introduced (i.e. it has been done in some areas but not in others nearby, which would facilitate clear comparisons), but it is important to explore the available, relevant data as far as possible, to glean the best evidence available. It is not intended to provide a definitive evaluation of the effects of badger removal.

Using data from the BTO/JNCC/RSPB Breeding Bird Survey, the authors examined the population growth rates of both ground-nesting and non-ground-nesting breeding birds over the period 2013–2019, and following five years of baseline data preceding commencement of culling (2008—2012). This enabled them to measure the effects of Badger removal on population change in the studied bird species, as far as the data allowed. Direct or indirect effects of Badger removal would be expected to be greatest on ground-nesting birds.

The study found little evidence to indicate consistent, community-level effects of Badger removal on the populations of ground-nesting birds. Ground-nesting birds will be predated by Badgers as well as by other predators, and populations of these other predators may themselves be influenced by Badger numbers. If the studied bird populations are regulated by predation, then it is likely to be by a complex suite of predators. However, it is also quite likely that predation plays no such role, and that factors such as food availability or land management are more important. All this means that changing the abundance of one predator may well have no overall effect on prey numbers in many contexts, and that the effects of removing a predator through culling will be difficult to explore definitively.

In analyses like this, the lack of an experimental study structure and of available information for other important variables (such as the density of Badgers pre-culling and Badger dispersal patterns) makes interpretation difficult. There are several reasons why effects of Badger removal might not have been found here, including limitations with the study design and a genuine lack of any real impact on bird populations. However, it is clear that there have not been strong, clear effects on species that should be more vulnerable.

Despite the limitations of the analysis, this study very clearly demonstrates the value of the Breeding Bird Survey dataset in observing long-term population trends, and one way in which it can be used in helping to monitor possible effects of large-scale policy measures on breeding birds.

Diversity of response and effect traits provides complementary information about avian community dynamics linked to ecological function

WEBSITEEDITOR — Wed, 03 Aug 2022 16:49:14 +0000

The Cuckoo cohort of 2024 takes flight!

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Hordley, L.A., Gillings, S., Petchey, O.L., Tobias, J.A. & Oliver, T.H. Functional Ecology 10.1111/1365-2435.13865

Functional diversity metrics based on species traits are widely used to investigate ecosystem functioning. In theory, such metrics have different implications depending on whether they are calculated from traits mediating responses to environmental change (response traits) or those regulating function (effect traits), yet trait choice in diversity metrics is rarely scrutinized.

Here, we compile effect and response traits for British bird species supplying two key ecological services—seed dispersal and insect predation—to assess the relationship between functional diversity and both mean and stability of community abundance over time.

As predicted, functional diversity correlates with stability in community abundance of seed dispersers when calculated using response traits. However, we found a negative relationship between functional diversity and mean community abundance of seed dispersers when calculated using effect traits. Subsequently, when combining all traits together, we found inconsistent results with functional diversity correlating with reduced stability in insectivores, but greater stability in seed dispersers.

Our findings suggest that trait choice should be considered more carefully when applying such metrics in ecosystem management.

The authors are very grateful to the thousands of volunteer recorders who contribute to the Breeding Bird Survey. The BTO/JNCC/RSPB Breeding Bird Survey is a partnership jointly funded by the BTO, RSPB and JNCC, with fieldwork conducted by volunteers. For access to specimens and assistance, we thank Hein van Grouw, Mark Adams and Robert Prys-Jones of the Natural History Museum, Tring.

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Inspired by birds, informed by science: providing the evidence-base for policy decisions

WEBSITEEDITOR — Fri, 08 Jul 2022 11:09:59 +0000

BTO Cymru’s Rachel Taylor and Callum Macgregor reflect on working at the interface between science and policy for their research on Cormorant and Goosander populations in Wales. No

Callum Macgregor

Senior Research Ecologist

Callum works as a Senior Research Ecologist analysing quantitative data from a range of projects from Wales.

Conservation often requires difficult decisions to prioritise one species over another. A current example of this is the plight of migratory salmonid fish (Salmon and, more recently, Sea Trout) in Wales. The problems facing these fish are complex, including changes in water quality, sedimentation and water flow in the freshwater environment and the impact of climate change at sea. Welsh Salmon populations are all declining and the species is designated ‘at risk’ or ‘potentially at risk’, even in the six Special Areas of Conservation (SAC) designated for them under the EU Habitats Directive. They are also a key feature of healthy freshwaters, and financially valuable to fishery managers, angling societies and the Welsh economy. Although a suite of pressures drives their decline, predation by birds presents a highly visible cause of salmonid mortality, and some stakeholders argue that lethally controlling fish-eating birds could have a positive impact on salmonid populations.

Atlantic Salmon leaping as they move upstream to spawn is considered a migration spectacle by many.

UK law protects all wild bird species, meaning a licence is necessary for any type of control. With a ’general licence’, it is legal to kill certain species including Carrion Crow and Woodpigeon, in order to mitigate a carefully-defined list of harms, such as significant economic damage, disease transmission risk, public safety or for the conservation of another ecologically-linked species. For other species, ‘specific licences’ are required to mitigate such harms, permitting the removal of a set number of individuals only. The control of Cormorants and Goosanders primarily falls under the second category, and embodies a trade-off between the conservation of the salmonid fish and birds. Licensed lethal control of both Cormorant and Goosander has already been happening in Wales for several years, but with fish populations still declining, Natural Resources Wales (NRW) recognised the need for all stakeholders to understand the implications of the conservation trade-off when making any new decisions. NRW convened a stakeholder group (Wales Fish-eating Birds Advisory Group) in 2018 for this purpose, and BTO was asked to participate as a scientific advisor.

Winter populations of fish-eating birds

A surveyor walks along the River Usk. Gethin Jenkins-Jones

The Group built a shared understanding of both fish and bird populations, identifying knowledge gaps and issuing contracts to address them. As part of this, the Group asked BTO Cymru to research the current and potential future population status of Cormorant and Goosander in Wales.

The first task was to design a survey, gathering data to inform current population estimates. This was challenging: the species are highly mobile, have poorly understood distributions and also have recent experience of human disturbance, including lethal control. The second task was to deliver that comprehensive survey across 10 major Welsh rivers and a representative sample of stillwaters.

After conducting the survey, we combined the survey data with data collected by BTO/JNCC/RSPB Wetland Bird Survey (WeBS) volunteers to calculate the size of the overwintering populations of Cormorant and Goosander during the winter of 2020-21.

The UK Cormorant population is made up of two subspecies, the coastal-breeding Phalacrocorax carbo carbo and the inland-breeding Phalacrocorax carbo sinensis. Welsh Cormorants are predominantly of the carbo subspecies.

We estimated there to be between 2,580 and 3,259 Cormorants overwintering in Wales. Around 40% of these were found on rivers, and 50% were found in estuaries. Our estimate was approximately half of previous suggestions derived from UK-wide estimates made by the Avian Population Estimates Panel (APEP). At the UK scale, the Cormorant population is made up of two subspecies (coastal-breeding Phalacrocorax carbo carbo and inland-breeding Phalacrocorax carbo sinensis), and the overall population is increasing. However, the Welsh population consists almost exclusively of the carbo subspecies, and is currently fairly stable in numbers but progressively decreasing in productivity. This means fewer chicks raised each year per adult, which could cause declines in future. As the previous estimates used UK-wide APEP data to estimate Welsh Cormorant populations, the estimate may have been inflated.

Our estimates for the overwintering Goosander population were slightly smaller, at 1,223 to 1,750 individuals, and were in line with previous estimates. The vast majority of Goosander were found on stillwater (almost 30%) or on rivers (around 70%), with only a few on estuaries.

We estimated there to be between 2,580 and 3,259 Cormorants overwintering in Wales, and 1,223 to 1,750 Goosander.

Neither species was evenly distributed across rivers, either along the length of the rivers or between different rivers. Numbers were higher near the river mouth than the source, and most birds were recorded on a few specific rivers. We found the greatest number of Cormorants on the River Dee, and Goosanders on the River Wye.

Spring populations and the smolt run

In Spring, male Goosander (top) departed to other areas to moult, while females (bottom) accompanied their young chicks.

The following spring (2021), the Fish-eating Birds Advisory Group contracted BTO to conduct an additional survey of the River Usk, a key river for spawning (breeding) Salmon which had the third- and second-largest numbers of overwintering Cormorants and Goosanders respectively. This survey was timed to coincide with the ‘smolt run’, a critical period in the life-cycle of salmonids, when young fish (smolts) undergo a profound metabolic shift to live in saltwater, and migrate en masse downstream to the sea. Smolts migrate overnight and rest at ‘pinch-points’ - places where the flow of the river is obstructed, like weirs, bridges or at natural barriers - during the day. During this migration, any smolt mortality means that fewer adults will return later to spawn. Smolts are especially vulnerable to predation at pinch-points, meaning opportunistic Cormorants and Goosander may have their most direct impact on salmonid populations at these points in migration.

The survey in spring found birds present in different densities and locations than those recorded in the winter survey. Cormorants were recorded at a much lower density, probably because the carbo subspecies moves back to breed at coastal colonies in spring. Although Goosander numbers were similar to those recorded in winter, the smolt-run coincided with a change in population composition: between the start and end of the survey, males departed, migrating to traditional sites (most likely in Scandinavia) to moult, and were replaced by the first broods of young birds, which were accompanied by females.

Alongside the spring Usk re-survey, BTO designed a further survey to investigate predation risk at known pinch-points on the river, comparing these with nearby unobstructed stretches of river. The survey was conducted by Afonydd Cymru volunteers, and found that Goosanders gathered in greater numbers, and invested greater fishing effort, at pinch-points during the smolt run than on other unobstructed sections of the river, or anywhere after the run’s conclusion. However, there was very little evidence to support targeted predation or high-intensity predation risk at pinch-points during the smolt run from Cormorants, or by other fish-eating species including Grey Heron and Little Egret.

Our third report modelled the future population trends of Cormorant and Goosander in Wales, to examine the potential outcomes of a range of scenarios of lethal control.

Evidence-based decision-making

Cormorant and goosander numbers recorded along the surveyed rivers. BTO

Sometimes, policy development requires difficult questions to be thought through fully before decisions can be made. In this case, the Advisory Group wished to understand what the implications of lethal control might be for Welsh populations of fish-eating birds. Our third report drew on the results of the winter and spring surveys, along with established population change data from the BTO/JNCC/RSPB Breeding Bird Survey (BBS) and the expert knowledge of a panel of BTO researchers, to model the future population trends of Cormorant and Goosander in Wales. We used this demographic modelling approach to examine the potential outcomes of a range of scenarios of lethal control.

Constructing a single demographic model carries a significant risk of error, because, at the population level, no two sites and no two birds will experience the same conditions nor live the same life history. To reduce this risk, we combined every possible set of the full range of feasible demographic parameters (like the number of offspring raised per adult per year, and the number of adults surviving each year) and generated 62,500 different population projections for each species. The truth was in there somewhere, and we used BBS data to select the subset of these population projections that best matched observed population trends, and could therefore plausibly be true in Wales.

Once we had selected these models, we applied different Cormorant and Goosander management scenarios, ranging from a 0% removal ‘business as usual’ scenario to an extreme case where 15% of the population of each species was removed each year. Cormorant populations were estimated to decline in future, even in the absence of lethal control (the 0% ‘business as usual’ scenario). In fact, 52% of the plausible models suggested a decline of 25% or over (which would trigger what is known as a ‘WeBS alert’) over a 25 year timescale. The proportion of models associated with WeBS alerts increased as the percentage of the population to be controlled increased, as might be expected. By contrast, the models suggested Goosander populations were on the rise, with 94% of plausible models predicting population increases under the 0% ‘business as usual’ scenario. However, higher levels of lethal control resulted in declines becoming more probable, including declines severe enough to trigger a WeBS alert.

It is personally and professionally challenging to work so closely with a decision-making process that, depending on NRW’s ultimate decision, may result in the lethal control of some Cormorants and Goosanders.

Outcomes - where next?

BTO’s design, survey and analytical work was written up as a suite of NRW Public Evidence reports, and (alongside several other reports from other organisations) presented to the Advisory Group for their consideration in framing recommendations to NRW about a new policy approach. At this stage, BTO’s role as scientific advisor included clarifying the outcomes (and limits) of the modelling, and answering any remaining questions about ecology or statistical confidence in the results, but we were not involved in deciding the Group’s recommendations to NRW.

The Group recommended that continued, or extended, lethal control of both Cormorant and Goosander was necessary to promote the recovery of salmonid populations in Wales. They also recommended several other actions, including continued monitoring and non-lethal management of predation risk (actions not involving fish-eating birds were outside the remit of this Advisory Group). The final stage is the responsibility of NRW, as the competent licensing authority, to make its own decision on whether to accept the recommendations of this document, and if so, what level of lethal control to apply for each species. These decisions will again be made with reference to the results of our work, especially the modelling of future population trends under different scenarios of lethal control.

It is personally and professionally challenging to work so closely with a decision-making process that, depending on NRW’s ultimate decision, may result in the lethal control of some Cormorants and Goosanders. BTO staff and supporters understand that conservation can involve difficult choices. But we should be proud that, whatever decision is reached by NRW, the best possible evidence concerning the population status of these birds in Wales, and a careful analysis of the likely impacts of lethal control, was available to the decision-makers. The recommendations of the Advisory Group, and NRW’s decision, will be made with a clear and unbiased understanding of the risks, or otherwise, to the birds we are so wholly invested in. And that is an encouraging thought.

BTO Cymru’s Rachel Taylor and Callum Macgregor reflect on working at the interface between science and policy for their research on Cormorant and Goosander populations in Wales.

July 2022 Providing the evidence for policy

BTO work delivers evidence needed to plan and assess conservation action, and informs decision-making processes about society, wildlife and the natural world. Indeed, many of our research activities - our surveys, the ringing scheme, GPS-tagging studies, and so forth - generate datasets that are ideal for this purpose. In the complex and sometimes contentious world of human-wildlife interactions, our impartial voice gives decision-makers confidence that our objective evidence can support and inform their work.

BTO Cymru

08 Jul 2022

Wales

Wild Rock Doves: solving a genetic enigma

WEBSITEEDITOR — Thu, 30 Jun 2022 09:23:00 +0000

BTO ringer and DPhil student Will Smith writes about his latest research into the distinctions between wild Rock Doves and the Feral Pigeon. No

Will Smith Limited domestic introgression in a final refuge of the wild pigeon (Smith, W. J. et al, iScience, 01.07.2022) Will is a DPhil student at the University of Oxford, studying population genomics in wild birds. He currently researches gene flow between wild and feral domestic populations, working in the field and the lab and in bioinformatic analysis.

Rock Dove / Feral Pigeon

Domestic and feral pigeons are important in a couple of ways. First, they are culturally significant. For every person cursing them as ‘rats with wings’, there are others who celebrate them as symbols of love and peace. There are few birds that turn up in mythology and symbolism as much as the pigeon does! More practically, the domestic and feral pigeon is a ‘model organism’, meaning that scientists use them to study behaviour, development, genetics, and urban evolution. Scientific papers are published every week studying different aspects of their biology, and they are therefore among the most understood species of animal in the world. Despite this, the wild ancestor of the domestic pigeon, the shy and retiring wild Rock Dove, is very poorly known.

Wild Rock Doves were originally found across vast swathes of Africa, Asia and Europe, occupying sea caves, clifftops and mountainous regions. They are wary birds which, unlike the variable domestic pigeon, only come in one plumage pattern, with a blue-grey body, two black wing-bars and a distinctive white patch on the lower back. Ever since Feral Pigeons have spread across the planet, they have been interbreeding with their much rarer wild cousins. In many places, this has led to the gradual replacement of Rock Doves with Feral Pigeons. In fact, presumed wild Rock Doves can now only be found in relict populations, often on islands, where they rarely meet Feral Pigeons. In Europe, such populations exist in certain parts of the Mediterranean, the Faroe Islands and the British Isles.

Extending the wing of a Rock Dove to show the species' plumage: a white patch on the lower back, two clean black wing-bars and lack of black chequering (which is present on hybrid or Feral Pigeons). Will Smith

Populations of Rock Doves and Feral Pigeons across the UK and ROI which were sampled as part of the project. Will Smith

Although English and Welsh Rock Doves have been extinct for many years, certain Scottish and Irish populations have occasionally been claimed to represent Rock Doves that have experienced negligible contact with feral pigeons. After watching wild Rock Doves mixing with feral pigeons in Caithness as a child, and reading about the similar history of the Scottish Wildcat (Felis silvestris) and domestic cats, I was keen to solve the puzzle of the Rock Dove’s genetics. We aimed to assess the genomic status of these birds, and, given the number of papers that are published every year on their abundant feral and domestic relatives, we hoped to shine a light on their contemporary situation for the first time.

As part of my doctoral project at the University of Oxford’s Edward Grey Institute of Field Ornithology, and in collaboration with British Trust for Ornithology bird ringers, we sampled presumed Rock Doves from various locations on the Atlantic fringe of Scotland and Ireland, as well as feral pigeons in the cities of Oxford and Manchester, rural regions in Yorkshire, Leicestershire and the Isle of Man, and a population in Shetland which is currently mixing with wild Rock Doves.

The support of BTO bird ringers was vital in ensuring the success of this endeavour, and their expertise in fieldcraft and bird behaviour allowed us to catch birds throughout the Scottish and Irish range of the Rock Dove, which represents a large chunk of their presumed European distribution. As well as taking simple biometrics (body measurements), we took feather samples to the lab to extract DNA for genetic analysis. DNA needs to be isolated from the feather samples before it can be sequenced and converted into a form where it can be analysed using incredibly powerful computers to explore similarities and differences between individual birds, and draw conclusions about the Rock Dove’s genetic history.

Fieldwork was often challenging and involved long nights in Outer Hebridean meadows, climbing through ruined buildings to study the doves as they roost. One of the privileges of this is getting familiar with all the other animals and plants that make their home there, including the Corncrake. These fascinating birds seem to purposefully move gradually closer and closer to the tent each day until they are shouting ‘crex-crex’, at maximum volume, all night, a metre from my head. At least Rock Doves don’t test an ornithologist’s patience quite that much!

Biometrics (body measurements) were taken from both Rock Doves and Feral Pigeons as part of the study. Here, the bill is being measured. Will Smith

Our genetic analyses indicated that, not only were the sampled populations likely to be representative of the ancestral Rock Dove lineage, but that some of them had indeed experienced very little genetic input from Feral Pigeons. In particular, Outer Hebridean Rock Doves have almost no detectable ancestry contribution from contemporary domestic or feral pigeons. We also identified physical differences between the wild and feral birds, especially relating to their head shape, with the wild birds having longer, thinner bills and a more pronounced forehead. This is of interest because the difficulty in separating the wild Rock Dove from its common relatives in the field has stymied research for many years.

These discoveries are exciting, and provide new avenues for scientific research, especially projects comparing wild, domestic and feral animals. We also hope that similar studies in different parts of the world could establish the genetic status of other relict populations of wild Rock Doves. Northern Africa, for example, might hold remnant populations of different subspecies. Our identification of Rock Doves will also allow them to be studied in their own right, rather than being lumped with feral pigeons as has often been the case in recent years.

Dive deeper into the research

Our study, “Limited domestic introgression in a final refuge of the wild pigeon”, is published in iScience.

The process of ‘genetic replacement’ that threatens the Rock Dove is happening in many different species as humans move animals and plants around the world. It is part of an increasingly homogenised global ecosystem. Biodiversity includes not only the number of species or extent of variation between ecosystems, but also genetic diversity, including the number of distinct groups or ‘lineages’ within a species. Genetic diversity is being eroded on multiple levels and due to multiple factors, ranging from inbreeding in small populations to interbreeding of previously distinct genetic groups. Research to understand how the process of genetic replacement happens is vital if we are to help conserve overall biodiversity at the genetic level. The undomesticated Rock Dove is just one example of a genetic lineage which is threatened with extinction as a distinct entity. We hope that by studying such biological phenomena, we will increase our understanding of the various risks to genetic diversity, which will help to inform conservation biologists studying and protecting many different species of animals and plants around the world.

BTO ringer and DPhil student Will Smith writes about his latest research into the distinctions between wild Rock Doves and the Feral Pigeon.

3 June 2022

Most of us who live in cities or towns will barely go a day without seeing a Feral Pigeon Columba livia. These birds are superbly adapted to surviving in urban environments, having descended from escaped domestic pigeons and followed humans as we spread around the world.

30 Jun 2022 no

The potential for analyses of monitoring scheme data to inform about the impacts of invasive on native species

VIOLA.ROSS-SMITH — Tue, 19 Apr 2022 13:40:35 +0000

The Cuckoo cohort of 2024 takes flight!

More Details

Pringle, H. & Siriwardena, G. Biological Invasions 10.1007/s10530-022-02785-8 UK animals and plants are surveyed annually by a wide range of long-term citizen science monitoring schemes, which are designed to detect species’ range, status and population trend. Here we explore whether these data are suitable for detection of ecological impacts of invasive species on native species. While expert horizon scans and risk assessments can identify those non-native species that are likely to turn invasive from ecological knowledge, it would be valuable to monitor such impacts in practice. Monitoring scheme data may support such evaluations. We consider the utility of monitoring data in this context via a series of case studies examining the detectability of impacts of Ring-necked Parakeet, Grey Squirrel and Reeves’ Muntjac on native birds and bats that are potentially vulnerable to their impacts. The results show that monitoring scheme data have the potential to provide novel insight informing the evaluation of invasive effects in a range of contexts, adding to current evidence bases, which typically rely upon ecological principles and evidence from small-scale studies. We found a combination of results supporting the expectation of invasive impacts and those not finding such effects. The latter may partly reflect limitations in data quality, such as issues of co-location of data, sample size, adequately detailed identification of at-risk habitats or locations, and likelihood of incompleteness of data on non-natives. We discuss options to enhance monitoring to support enhanced analyses in the future, but analyses of the data can already provide evidence to assist with the determination of invasive impacts now.

The authors thank all the volunteers who have participated in BBS and BCT, and the survey organisers. BBS is funded by a partnership of BTO, JNCC and RSPB. The authors also thank Philip Briggs and Becky Wilson for providing BCT data and advice, and Niki Newton and Niall Moore for comments on earlier drafts. The authors are grateful to an anonymous reviewer and Guillaume Latombe for their helpful comments and feedback.

Long-term citizen science monitoring schemes are designed to detect species’ range, status and population trends, and are already used to track the arrival and spread of invasive species. However, they could also be a valuable source of data for researchers looking to assess the impact that established invasive species have on native species.

The impact of an invasive species could be revealed through three types of relationships with native species: a status-status comparison, in which the native species is rarer where the invasive species occurs or is more common; a status-change comparison, in which the native species sufferers more declines were the invasive species occurs or is more common; or a change-change comparison, in which more negative population effects are observed in the native species when more positive effects are observed in the invasive.

In this study, the researchers evaluated the possible uses of citizen science data for detecting these ecological impacts of invasive species on native species. Using data from the BTO/JNCC/RSPB Breeding Bird Survey (BBS) and the National Bat Monitoring Programme (NBMP) the researchers conducted four case studies employing different methods of data processing - for example, summarising data over different spatial and temporal scales depending on the taxa recorded.

For each case study, the researchers identified the association between invasive presence or abundance and native species’ responses, and assessed the strengths and limitations of the datasets used. For example, the first study used BBS data covering the same time period and spatial scale, collected using BBS methodology. This made the analysis more robust than that in the final case study, which used data from BBS and the NBMP. As the data had been collected in different surveys, there was less spatial and temporal overlap and the resolution of the BBS data analysis was limited by the survey methodology of the NBMP.

The researchers concluded that data from existing national biodiversity monitoring schemes could be used to assess the impact of invasive species on native ecology, but several limitations do exist in these datasets. Firstly, invasive effects need to be identified rapidly after arrival when the species is still rare or localised, but national-scale monitoring is not likely to collect enough high-resolution data at this early stage to inform eradication programmes. Secondly, abundance data for many groups of interest are lacking, as schemes have focussed on recording simple presence/absence data. Thirdly, many schemes collect data on taxa other than those originally targeted; for example, while BBS has all the advantages that come from a structured, standardised survey, it was not designed specifically for recording mammals and therefore may report more ‘false absences’ than a specialist mammal survey due to differences in mammal and bird detectability.

In order to enhance analysis options, the researchers suggest combining the data quality of structured surveys (such as BBS) with the data quantity of unstructured schemes (such as opportunistic recording), and encouraging counts of individuals (or cover measures for plants)rather than simple presence/absence data.

The future distribution of wetland birds breeding in Europe validated against observed changes in distribution

VIOLA.ROSS-SMITH — Wed, 26 Jan 2022 16:50:43 +0000

The Cuckoo cohort of 2024 takes flight!

More Details

Soultan, A., Pavón-Jordán, D., Bradter, U., Sandercock, B., Hochachka, W., Johnston, A., Brommer, J., Gaget, E., Keller, V., Knaus, P., Aghababyan, K., Maxhuni, Q., Vintchevski, A., Nagy, K., Raudonikis, L., Balmer, D., Noble, D., Leitão, D., Øien, I.J., Shimmings, P., Sultanov, E., Caffrey, B., Boyla, D., Radišić, Lindström, Å., Velevski, M., Pladevall, C., Brotons, L., Karel, Š., Rajković, D.Z., Chodkiewicz, T., Wilk, T.,. Tibor, S., van Turnhout, C., Foppen, R., Burfield, I., Vikstrøm, T., Mazal, V.D., Eaton, M., Vorisek, P., Lehikoinen, A., Herrando, S., Kuzmenko, T., Bauer, H-G., Kalyakin, M., Voltzit, O., Sjeničić, J. & Pärt, T. Environmental Research Letters 10.1088/1748-9326/ac4ebe Wetland bird species have been declining in population size worldwide as climate warming and land-use change affect their suitable habitats. We used species distribution models (SDMs) to predict changes in range dynamics for 64 non-passerine wetland birds breeding in Europe, including range size, position of centroid, and margins. We fitted the SDMs with data collected for the first European Breeding Bird Atlas (EBBA1) and climate and land-use data to predict distributional changes over a century (the 1970s–2070s). The predicted annual changes were then compared to observed annual changes in range size and range centroid over a time period of 30 years using data from the second European Breeding Bird Atlas (EBBA2). Our models successfully predicted ca. 75% of the 64 bird species to contract their breeding range in the future, while the remaining species (mostly southerly breeding species) were predicted to expand their breeding ranges northward. The northern margins of southerly species and southern margins of northerly species, both, predicted to shift northward. Predicted changes in range size and shifts in range centroids were broadly positively associated with the observed changes, although some species deviated markedly from the predictions. The predicted average shift in core distributions was ca. 5 km/year towards the north (5% Northeast, 45% North, and 40% Northwest), compared to a slower observed average shift of ca. 3.9 km/year. Predicted changes in range centroids were generally larger than observed changes, which suggests that bird distribution changes may lag behind environmental changes leading to "climate debt. We suggest that predictions of SDMs should be viewed as qualitative rather than quantitative outcomes, indicating that care should be taken concerning single species. Still, our results highlight the urgent need for management actions such as wetland creation and restoration to improve wetland birds' resilience to the expected environmental changes in the future.

We are very grateful to European Bird Census Council (EBCC) and all its contributors and GBIF for providing, curating, and making publicly available occurrence data from the EBBA1. We also acknowledge people and institutions that make public all the environmental data that we used in this research. Thanks to EBBA2 contributors for providing us with their recently published data. We also acknowledge the Scientific Project of the State Order of the Government of Russian Federation to Lomonosov Moscow State University No. 121032300105-0 for participating in EBBA2 data. Our research was funded through the 2017–2018 Belmont Forum and BiodivERsA joint call for research proposals, under the BiodivScen ERA ‐ Net COFUND program, with the following funding organizations: the Academy of Finland (Univ. Turku: 326327, Univ. Helsinki: 326338), the Swedish Research Council (Swedish Univ. Agric. Sci: 2018–02440, Lund Univ.: 2018–02441), the Research Council of Norway (Norwegian Instit. for Nature Res., 295767), and the National Science Foundation (Cornell Univ., ICER-1927646), and we also acknowledge the Swedish Environmental Protection Agency.

Out in the Field

WEBSITEEDITOR — Thu, 20 Jan 2022 10:53:56 +0000

BTO Youth Rep Gethin Jenkins-Jones shares his experience surveying the River Usk to collect data on Cormorant and Goosander populations. No

Gethin Jenkins-Jones BTO Youth Rep

Gethin is a 22-year-old nature enthusiast from Cardiff and a graduate of Conservation Biology and Ecology at Exeter University. He has been a keen birder since childhood and enjoys sharing his passion for wildlife with others.

The fieldwork in question was all due to the status of Welsh Salmon. When Wales was pristine, Atlantic Salmon filled the rivers annually, providing good sport and food for local communities, but many stocks around the country have declined in recent decades and it is now a protected species.

Among many factors that could be driving these declines is predation by Goosanders and Cormorants, leading Natural Resources Wales (NRW) to grant licences to shoot a limited number of each species in recent years. To assess if this action might have unintended consequences for Cormorant and Goosander populations, NRW engaged the BTO to organize a robust survey estimating the winter populations of these birds along Welsh rivers.

Having spent virtually the entire autumn around Cardiff, the thought of fieldwork was refreshing - but before I got the contract, I needed to complete an online bird identification test. Although I passed, I was surprised (and I know others who agree) how tricky IDing the call of some species can be when you remove the context of habitat, season and region. I was glad to overcome that hurdle!

I was designated the River Usk, a 125-kilometre river that flows south-east from the northern slopes of the Black Mountain in the Brecon Beacons to the city of Newport. In late November I was mailed copies of the maps I would use in the field, which divided the river into 13 10-km sections for me to survey. There were also other documents to get my head around: risk assessment, methodology, travel expenses sheets, electronic forms to complete after each survey, and a document to present to people to justify my presence in the area. After a Zoom call with the rest of the team to clarify everything, I was almost ready to go!

A tributary of the River Usk. Gethin Jenkins-Jones

Preparing for each section followed a similar routine. First, I studied the maps a day or two before going to the field, taking note of the general landscape, potential obstacles and, most importantly, which side of the river was most suitable to walk along. For the first few sections, the maps also helped me decide what footwear to bring, although following heavy rain I took no chances and wore wellies for every section. The next step was to fill my rucksack with all the necessary equipment: a GPS, plenty of food and water, relevant paperwork, a first aid kit, and the clipboard with the maps to record my findings. Before I started each section, I recorded the weather, the width of the river and the date and time, and then I set off.

Although most of the survey involved walking through fields, sometimes I needed to overcome obstacles to complete sections. The most difficult were a couple of tributaries that had no crossing bridge and were too wide for me to jump over. To avoid a huge detour, I decided to find suitable fallen trunks to crawl along to the other side. Both left me wet and muddy, though thankfully both supported my weight!

Heavy snow and wet mires presented some difficulty, and in one incident I sank beyond the height of my wellies, which made the remainder of the section a lot less pleasant. One other common obstacle - which often led to the destruction of my clothing - was barbed wire. Most fences were low enough to enable me to climb over with no difficulty, but some were higher, and repeated snagging of the barbs against my field trousers left them virtually shredded by the end of February, giving me the appearance of a character from Oliver Twist. (The trousers were duly recycled once I had finished).

Some birds were total surprises, like Mandarin, wintering Goldeneye, and Green and Common Sandpipers.

Sheep on the footpath. Gethin Jenkins-Jones

Having lived in a city all my life, one unfamiliar thing that was frequent throughout the project was total solitude. Conversations with people during the surveys were few and far between and, other than the odd conversation with curious (but mostly friendly) landowners, I was often completely alone in open country. For large stretches there was not a soul in sight and sheep were my only company. Some galloped towards me, some looked at me with bored indifference, whilst others fled in fright to the far end of their field. One flock even followed me for several hundred metres along a footpath! I was surprised (and a little disgusted owing to their ecological impact on my country) by the sheer number of these animals I encountered along the Usk and its tributaries, even knowing my nation’s reputation.

The diversity of bird species I encountered exceeded my expectations. Having grown up near the River Taff - a close neighbour of the Usk - I expected to see similar species, but what I encountered was a completely separate ecosystem with far greater biodiversity. At times it honestly made me wish this was my patch instead! In total, I saw around 2,000 birds of 23 different species, including some that were total surprises, like Mandarin, wintering Goldeneye, and Green and Common Sandpipers. I noted every species down on the maps provided using the standard Breeding Bird Survey species codes, and I also noted the behaviour and GPS location for the Goosanders and Cormorants - whether they were swimming, feeding, flying or resting. Upon seeing these birds, I tried my best not to flush them upriver, to avoid ‘double counting’ them later.

Gethin Jenkins-Jones

Most sections took between three and four hours to complete, which meant there was always plenty of time to relax after I arrived back home. To enter my data, I filled in an online form and noted the six-figure grid references for the non-target wetland species. I also recorded the GPS coordinates for the target species, as well as any other field observations of interest. After completing the main river channel in December, I compared my counts with those that anglers have published. My number of Cormorants was similar, but my Goosander counts were barely 25% of their reported estimate.

When I completed my final section on the penultimate day of February and posted my final field maps and forms, I had walked almost 300 km (185 miles), had seen some fantastic wildlife and had seen places that I never expected to see. I wondered how many other people had walked the entire river. I had walked along ancient paths that might not have been walked upon in years, and had seen derelict farmsteads that stood as surviving pages of long-lost chapters of my country’s past. I now feel that I have a better understanding of Wales itself, and doing this survey has further solidified my desire to pursue a career in conservation.

BTO Youth Rep Gethin Jenkins-Jones shares his first experience working for BTO.

2 January 2022 Collecting data for the Cormorant cull debate

After three wonderful years studying Ecology and Conservation at Exeter University, I was very happy to have my first environment-themed job soon after returning home in late summer. And looking back, it was as much of an adventure as it was work, leaving me with some fantastic memories.

Gethin Jenkins-Jones

20 Jan 2022

BTO Youth

Wales