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


Wednesday, 10 July 2019

Autumn migration gets underway

There has been a lot of chatter both on social media and elsewhere that this has been a poor spring for some of our most loved summer migrants, particularly Swifts, Swallows and House Martins. Looking at the BirdTrack reporting rate graphs for these three species, all of them were reported at lower levels compared to their historical averages. Swallows arrived bang on time, whilst House Martins initially appeared to be arriving earlier but then dropped below the historical average and Swifts were around 1-2 weeks late. A cold northeasterly airflow could explain the drop in House Martin arrival in week 15 (WC 08/04/2019) which is also noticeable on the Swallow plot. The delay in arrival for Swift is also most likely due to an easterly airflow during week 16, which then turned to a southerly airflow during week 17 and in turn produced an upsurge in Swift sightings.

We will have to wait until the publication of 2019 BBS (Breeding Bird Survey) report in May 2020 before we can asses any population changes for these three species.

Back to the here and now, July migration is headlined by waders such as Spotted Redshank, and Green Sandpipers, which are amongst the first to head back. The females of both species are the first to depart as they leave the males to incubate the eggs and raise the young. The males and young of both species migrate later and start to appear in late July and early August. Green Sandpipers can turn up anywhere from saltwater lagoons on the coast to small vegetated ponds inland, their distinctive white rump in flight gives the impression of a large House Martin, and a high pitched three-note whistle is often given during flight. See the Green Sandpiper identification video for more.

Green Sandpiper - Vic Froome

Storm Petrels breed at a few locations in the UK, mainly on Scottish Islands and a few Islands off the coast of Wales, South West England and the west coast of Ireland. In July however, they are often recorded away from these traditional breeding areas and it is a long-held belief that these relate to ‘Wanderers’, non-breeding or failed breeders that are looking for potential new breeding areas. These movements can be rapid and over large distances, as illustrated by a bird ringed in Norway that was caught 613km away in North Yorkshire the very next day.

NOS Adult 26-07-2002 Lindesnes Fyr, Lindesnes:57°58'N 7°3'E(Vest-Agder) Norway

E760828 Caught by ringer 27-07-2002 Upgang, Whitby:54°29'N 0°38'W(North Yorkshire)   613km  SW  0y 0m 1d

Storm Petrel - Joe Pender

For more, please visit the BTO Storm petrel identification video

All of the BTO satellite tagged Cuckoos have now left the UK and have reached their first stopover sites in southern Europe. This year BTO scientists are following 11 satellite-tagged Cuckoos as they make their way to central Africa. Currently four of them are in France, six in Spain and one in Croatia, unfortunately, a twelfth bird was killed flying into a window at Dungeness. Having moved from Sherwood Forest, Nottinghamshire, this bird, named Robinson, was well on its way south. Migration is full of hazards. Follow the Cuckoos as they undertake their huge southward journeys at

During the last couple of weeks there has been a large arrival of Painted Lady butterflies into the UK off the back of warm south and southeasterly airflow, two birds almost certainly arrived on the same weather system, the Little Bustard in Gloucestershire and the Blue-cheeked Bee-eater in Highland - if the Painted Lady invasion continues as the weather begins to warm again next week, we might be in for a summer mega.

What to look out for during the rest of July.

At this time of year, south westerlies can produce Cory's Shearwaters and Balearic Shearwaters, with headlands in the south-west the best place to sea watch from. A pelagic trip from the Isles of Scilly could result in sightings of the once mythical Wilson's Petrel.

Together with the more expected Green, Common and Wood Sandpipers, other vagrant wader species can often be found in late July with Terek, White-rumped, Pectoral and Buff-breasted Sandpipers being the most likely.

Other species on the move in late July include Quail, Little Gull, Black Tern,  and Common Scoter, with the latter species often turning up on inland reservoirs so keep an eye out for these.

Little Gull - Graham Catley

At the moment there is also a small influx of Two-barred and Common Crossbills happening, mainly on the Shetland Isles. The last influx was July 2017 and was confined to Shetland Isles with the exception of a single female on the Isle of May. In  2013 the influx was more widespread with birds scattered across the UK, will the same happen this year? A few Common Crossbills have been seen as far south as the Isles of Scilly, so it may be worth checking your nearest coniferous woodland. Larch cones are the favourite of Two-barred.

A Sooty Tern seen this year on the 24th June along the Yorkshire coast was subsequently seen again on the 9th July and is probably the bird from last year that was first seen on 7th July 2018 disappearing between  9th-19th July before relocating to Ythan Estuary where it stayed from 21st July -5th August. Perhaps it will head back there again this year?