BTO migration blog

Spring and autumn are exciting times for anyone who watches birds. Here on this blog we will make predictions about when to expect migrant arrivals and departures, so that you know when and where to see these well-travelled birds.

Thursday 15 August 2019

Migration moves up a gear.

Looking back at the last migration blog we highlighted the small influx of Two-barred Crossbills that was happening on the Shetland isles. The influx slowed towards the end of July with numbers steadily dropping off, but recently a few more birds have been reported including some from the Outer Hebrides indicating that these birds may be continuing to move around. A check of your nearest coniferous woodland could be worthwhile!
During the last weeks of July and early August, both Wood and Green Sandpipers were reported above their historical averages with the most likely explanation for this being easterly winds across the Baltic and the North Sea on 27th/28th July pushing birds across to the UK where they hit a belt of rain that straddled the country and forced them down. A video showing how to identify Wood and Green Sandpipers can be found here.

BirdTrack reporting rate graphs showing the spike in both
Green and Wood Sandpiper reports in late July/early August

As the year slowly ebbs from late summer into early autumn migration steps up a gear and the range of species and the number of birds on the move increases. August is the month for waders and seabirds, but some passerines also have their peak autumn migration at this time of the year.
Adult waders, whose numbers began to build in July will be joined by this year young leaving their northern breeding grounds for the very first time. Numbers of Knot, Redshank and Dunlin increase during the month and impressive counts of these species can be recorded at favoured sites. Towards the end of the month they will be joined by smaller numbers of Wood Sandpipers, Curlew Sandpipers and Little Stints, many of which will be in fresh juvenile plumage. Of course, it is always worth searching amongst these for rarer waders – such as Pectoral, Semipalmated, Baird’s and White-rumped Sandpipers that can arrive here from America. Weather systems arriving from across the Atlantic, often the remnants of a hurricane or severe storms, can result in good numbers of these rarer species appearing on our shores. Easterly winds could also produce something rarer such as Sharp-tailed Sandpiper, Red-necked Stint or dare we dream of another Little Curlew, the only 2 British records of this species have both occurred in August.

Juvenile Little Stint - photo by Vincenzo Iacovon

Seabirds are also on the move this month, some of them heading back to the southern hemisphere for the forthcoming breeding season, and now is a great time to look out for Cory’s and Great Shearwaters, and Wilson’s Petrel. Invariably headlands in the southwest are the place to be for these oceanic wanderers and again Atlantic depressions with their associated strong winds can force large numbers of these species closer inshore. Manx Shearwaters are at their highest reporting rate in August as the adults head to winter off the coast of Brazil leaving the young to fend for themselves and make the journey unassisted. Numbers of scarcer species including Sabine’s Gull and Long-tailed Skuas increase markedly at this time of the year and both are a desirable species for many sea watchers. An identification video on skuas can be found here.

Sabine's Gull - photo by Moss Taylor

Whilst Common and Arctic Terns will be becoming less frequently reported during the month, both Black Terns and Roseate Terns have a peak in their respective reporting rates in August. Black Terns can turn up almost anywhere from reservoirs to coastal sites and often associate with Little Gulls. This small tern has a distinctive dipping feeding flight as they pick insects from or just above the water and it is worth checking any likely locations after a heavy thunderstorm to see if any have dropped in. Roseate Terns, on the other hand, are almost exclusively found at coastal sites, the very clean white upperparts and dark bill of adult birds pick them out from both Common and Arctic Terns, whilst young birds have the scalloped plumage reminiscent of juvenile Sandwich Terns.

Black Tern - photo by Graham Catley

It’s not all about waders and seabirds through – August is probably the best month to go in search of Aquatic Warbler in Britain, though it is no easy task. This species has a very varied status in the UK, once it was an extremely rare bird but following some concentrated ringing, particularly around reedbeds in the south and southwest, annual totals began to rocket with the period between 1972-1977 being the golden era with 1976 producing a record 88 individuals. Hotspots included Radipole and Marazion marshes, indeed Devon has 107 records and Cornwall 154. Numbers then fell away in the ’80s and 90’s interspersed with a few good years, but in the last 10 years, annual figures have struggled to reach double figures with a declining population in their European breeding grounds of Eastern Poland the most likely cause.

Aquatic Warbler - photo by Dawn Balmer

Tree Pipit, Pied Flycatcher, Redstart, Willow Warbler and Spotted Flycatcher all have an autumn peak in reporting rates in August. The reporting rates for Whinchat also typically beings to increase throughout the month with birds turning up inland and at coastal watchpoints, sometimes in small groups. Some scarcer passerines to look out for during the month include Greenish Warbler and Icterine Warbler, both have a similar breeding range of northeastern Europe and varying numbers occur in the UK each autumn particularly after spells of easterlies. Even rarer,  Yellow Warbler a very rare American vagrant that has been recorded in the UK during August on 5 occasions with the last 2 records both occurring last year at Portland, Dorset and Mizen Head, Cork.
BirdTrack reporting rate for Pied Flycatcher showing
 a peak in autumn migration in August.

Pied Flycatcher, autumn is when many birdwatchers see this
species away from their traditional breeding areas.

By the end of the month, Swifts will become thin on the ground as they leave the UK on their long journey south to the Congo Basin and the first finch flocks will begin to feature in visible migration counts.
Don’t forget the Spurn Migration Festival, held over the weekend of 6-8th September – celebrating bird migration through walks, talks, and workshops on and around the Spurn Peninsula, East Yorkshire.

Scott Mayson and Paul Stancliffe