BirdTrack migration blog (19th-25th August)

It's unlikely that we'll understand the full impacts of this extreme weather for several months, until the data on life history stages like breeding and mortality are analysed.

Alongside the heat, avian influenza has had a devastating effect on several seabird colonies, with the full impact of this taking potentially years to understand because of seabirds' long lifespan.

Both the hot weather and avian influenza could have knock-on effects on migration, especially for birds which visit the UK in summer to breed. Will productivity (the number of offspring successfully raised to fledging) be down, meaning fewer migrant passerines such as warblers, chats, swallows and martins, and flycatchers will be on the move? How intense will seabird migration be, given the vast numbers of seabirds that have died this summer? Only time will tell. 

The last couple of weeks have seen a pulse of early migrants. Pied Flycatcher has seen an increase in the BirdTrack reporting rate, as large numbers of birds were seen across Britain and Ireland. 

Last month's species focus was on Aquatic Warbler,  and the run of southeasterly winds certainly produced the goods with eight of these stripey warblers reported in the last week. With a similar weather forecast during the coming week, more are likely to be found, so keep your eyes and ears peeled.

Reports of Chiffchaff, Willow Warbler, Whitethroat, and Blackcap all increased in the last week as birds begin to head south for the winter, and these were joined by the first Whinchat and Wheatear of the ‘autumn’, giving us a hint of what to expect in the coming few weeks as the intensity of migration builds.

The dry conditions have resulted in several Spotted Crakes being reported, no doubt partly due to birds being forced into the open as they search for food along muddy edges.

Species focus - Cory's Shearwater

Cory’s Shearwater is a fascinating species. Breeding during the northern summer in the Atlantic archipelagos of the Canaries, Berlenga’s, Salvegen’s and the Azores, on Madeira, and in the western Mediterranean, it begins to vacate its colonies during late autumn. It can be seen in varying numbers each year off our coast during the late summer, mainly in the southwest but with smaller numbers off the east coasts too.

In some years, many Cory’s Shearwaters are seen in the Bay of Biscay. Cory’s Shearwaters only begin breeding between 5 and 13 years of age, and it is thought that the Bay of Biscay records are mostly non-breeders, as some of these immature birds venture further north into the northwest Atlantic and British and Irish shores. The birds we see from UK coasts are those heading back south into the Bay of Biscay and then onwards to South Africa and South America on their epic annual migration. The numbers of birds and their distribution in the Bay of Biscay varies between years; it is in years when there are more significant numbers distributed further north that ‘big’ influxes can occur off Britain and Ireland.

The best places to catch up with this very marine species are off southwest coast headlands, such as Porthgwarra, Cornwall, from Boats around the Isles of Scilly, and off southwest Ireland where Cape Clear stands out.

BirdTrack is a great way of charting influxes of birds like Cory’s Shearwater as sightings can be heavily weather-dependent, with the timing and intensity of reports varying from year to year. 

Looking ahead

A short respite from the intense heat is forecast for the coming week, along with some welcome rain. The wind will be predominantly from a westerly direction, but there will be times of east/southeasterly airflow.

The westerly winds are likely to lead to a reduction in drift migrants arriving along the east coast, instead being more conducive for sea watching, particularly along the south-westerly coasts. Seabirds on the move at this time of year include Manx, Cory’s, and Great Shearwaters, with Manx Shearwater being the commonest species. What has been a poor year so far for Balearic Shearwater could change in the coming days, and places like Portland, Dorest and Porthgwarra, Cornwall are ideally situated to search for them amongst the commoner Manx Shearwaters. Storm Petrel, Kittiwake, and Great Skua will also be on the move; with the devastating effects of avian influenza on Great Skua colonies in Scotland, it will be interesting to see how well they are reported over the coming weeks. 

At this time of year, winds coming off the Atlantic have the potential to bring some American waders to our shores, with Pectoral, White-rumped, and Semipalmated Sandpipers being the commonest species. American Golden Plover, Baird’s Sandpiper, and Buff-breasted Sandpiper are also possible, and any flock of small waders are well worth going through to see if you can find your own.

With a more easterly wind direction forecast at the start of next week, the focus will change to drift migrants coming across from the near-continent and arriving along the east coast. Redstart, Spotted and Pied Flycatcher, Graden Warbler, Lesser Whitethroat, Wheatear and Whinchat are all to be expected at this time of year and any scrub or stands of trees near the east coast are worth a check, given the right conditions. Keep a look out for scarcer species like Wryneck, Icterine Warbler and Barred Warbler too.

Have you seen a rarity?

Or perhaps you're looking to find a passage wader?

Tell us about your migration birdwatching in the comments below.