Warbler watcher’s week

Sedge Warbler migration is at its peak; large numbers of this intricately-marked warbler are passing through watchpoints on the south coast right now. This was illustrated perfectly at a bird ringing site on the Pett Level in East Sussex this weekend - a team from BTO joined the regular ringers to help get a handle on the huge volume of birds leaving the country at the moment and of more than 2,000 birds caught and ringed, about 25% were Sedge Warblers. The Birdtrack reporting rate shows perfectly how this species is flooding out of the UK.


Other species that were well represented included Willow Warbler and Whitethroat, whilst Sand Martins - our earliest departing member of the swallow family - far outnumbered Swallows at the evening roosts.

Common Terns have become more obvious offshore as they make their way south in migrating flocks. 2,530 were counted past Spurn Point on 16 August. Flocks of migrating terns flying just above the waves determinedly heading south provide one of the greatest spectacles of autumn migration. However, this week the Terns at Spurn were been eclipsed by Swallows- 7,500 were counted heading south over there on the same day. Over the next few weeks the number of these two species should increase as more and more begin their migrations.



The first juvenile cuckoos are also beginning to appear at coastal watchpoints. It is interesting to think that some of these could be the youngsters of the BTO satellite-tagged cuckoos that are being followed to their wintering grounds, which are already south of the Sahara.

Question of the week - What triggers migration?

It is largely recognised that there are two types of migration. Obligate; controlled by genetics, and facultative; controlled by external factors such as local weather conditions. For birds such as Swallows, terns and cuckoos, it is obligate migration that we are interested in.

Change in day length is an important factor in the timing of migration for obligate migrants, and coupled with genetic influence, can give greater year-to-year consistency in the timing of migration in individual species. For example, British Swifts largely tend to leave the country during the first week of August.

Birds are already on the move

For those following our five satellite tagged cuckoos this will come as no surprise, with four of them already south of the Sahara desert. However, lots of other birds are also leaving the UK, probably the most noticeable being the Swift.

All summer they have been screaming around our streets and houses but have disappeared during the last week. Many of these could already be well south of the Sahara and close to their winter quarters.

Willow Warblers have also been flooding out of the country with numbers in excess of one hundred birds being counted at some south coast migration watchpoints; these have often been in the company of smaller numbers of Common Whitethroats.

Another warbler, the Grasshopper Warbler, probably sneaks out of the country largely unnoticed but at one ringing site in Hampshire, 267 have been trapped and ringed during July alone, all but one of them being young birds.

Ospreys are also on the move, and now is a good time to catch up with one of these impressive raptors. Although they often still associate with waterbodies, a bird on active migration could be seen anywhere as it makes it way south. During the last week, Ospreys have been seen in 24 British and Irish counties.

Question of the week.

Why do birds migrate?

This is a very difficult question and to answer this we probably have to look back to the last Ice Age, around 10,000 years ago. At this time, large parts of northern Europe were under ice, which will have retreated north during the summer months only to return during the colder winter months. As the ice retreated north, uncovered habitat will have been exploited by birds from further south that themselves have retreated south as the colder months returned.

As the planet warmed and the southern edge of the ice retreated further and further north, birds will have moved further north during the summer months and flown greater distances back during the winter months; migrating.

Today, the conditions during the winter months are still unsuitable for many of our summer migrants, although we are seeing evidence of more species attempting and succeeding to stay in northern Europe during the winter months. In recent times, several species of warblers, Swallows and a few Turtle Doves have all been recorded in the UK during the winter. These pioneers stay much closer to their breeding area than those that have left the country and, in theory will have first choice of prime territories come the breeding season, ensuring that their offspring get the best start.

Migrants just keep coming

North-easterly winds and the second week of June wouldn’t ordinarily be the perfect recipe for the arrival of migrant birds.  

Common migrants continue to arrive albeit in smaller numbers and included Spotted Flycatchers, Swifts and House Martins, the notable exception to this being Common Crossbills, flocks of which have been reported as heading south from Shetland to Dorset, the likely origin of these birds being Scandinavia.

Crossbill by Andy Mason

The remarkable migration of this spring just keeps on going. At times the north-easterlies have been quite light and during these conditions it was inevitable that a few birds destined for places east of the UK would turn up, drifting west as they tried to make headway north. As predicted last week, the north and east of the UK would be the place to be, and as it turned out it is where a lot of birders had to be as the third White-throated Robin turned up in Cleveland.

Other scarce and rare birds included three Red-footed Falcons, two on the east coast but the third was found in Herefordshire, up to fourteen Common Rosefinches, several Red-backed Shrikes and Icterine Warblers, a small number of Marsh Warblers and singles of Bee-eater, on the Isles of Scilly and Hoopoe in Dorset.

The wind for the next few days will come from the west and south-west and will be strong at times, this in effect should pretty much bring migration to a halt with the exception of Manx Shearwaters which could continue their movements along the west and south coasts in particular.

Manx Shearwater by Joe Pender

What will this mean for the 5 Cuckoos we are satellite tracking? If the wind is as strong as it is forecast to be Chris will probably hang around in Sussex, with Martin, Kasper and Lyster staying put in East Anglia. Clement might be the only bird to move as the lighter westerly winds in southern France help him on his way east. Take a look at the maps to see what happens and don't forget you can help this project by sponsoring one of our Cuckoos.

A BTO project is using satellite tags to track Cuckoos to their wintering grounds

Weather slows migration

It's been much quieter this week, more due to the weather than to the end of migration. Migration should continue for at least a couple more weeks yet with the focus turning to the north as some late migrants and overshoots arrive there.

Spotted Flycatchers and Quails have arrived in small numbers this week and there have been some small movements of Swifts and House Martins on the east coast.

Above: Quail by Abbie Marland

On the rarity front, six new Red-footed Falcons were found this week and East Sussex recorded its first ever Pallid Swift. Despite the weather, another three Bee-eaters were reported this week and a single Hoopoe on Lundy, Devon.

It really has been a Red-rumped Swallow spring and another four were reported this week from Scilly to East yorkshire.Putting all these in the shade a Least Sandpiper from North America was found in South Yorks yesterday.

The weather is to remain mixed for the next few days but birds will move whenever the wind drops and a rarity in the northern isles is very much on the cards, and could still prove to be a sparrow from North America.

Migration slows down

It's been a much quieter week this week and it really does seem like the main thrust of migration is over. However it appears that there are still good numbers of House Martins missing from breeding colonies and these birds could arrive any time.  Rarities continue to turn up and this week has seen a Gull-billed Tern in Norfolk, Black-winged Stilt and yet another Red-rumped Swallow, this time on the Isles of Scilly. Not a day seems to have gone by this Spring without a Red-rumped Swallow or a Bee-eater somewhere in the country.  

Bee-eater by John Harding

The weather continues to come from the west and this will largely keep any movements down, particularly when the winds are of any strength.  Migrants will continue to arrive for at least another 2 weeks and we should see those tardy House Martins and Spotted Flycatchers.  We are also just coming in to the peak time for Quail.

Don't forget if you want to listen to Nightingales in song, they will only be singing for the next two weeks, going quiet at the beginning of June.   The Nightingale is one of our fastest decline summer migrants, if you would like to help us find out more about the reasons for the decline, please support our new Nightingale Appeal.

Above: Nightingale by Edmund Fellowes

Extraordinary week's migration

Last week was an extraordinary week, although the predicted Sociable Plover failed to show, it was a week for rare waders, with at least three Buff-breasted Sandpipers being reported and singles of Broad-billed Sandpiper and Kentish Plover in Cumbria, Spotted Sandpiper in Buckinghamshire, and Lesser Yellowlegs and Great Snipe in Norfolk, the latter in full display for one evening and one morning only.

Above: Calandra Lark by John Harding (not the Lincs bird)

Along with the Collared Flycatcher, mentioned in the last blog, Britain’s fourth Rock Bunting, and the first since 1967, was seen and photographed in North Yorkshire and subsequently identified from the photograph. An Audouin’s Gull in Suffolk took the British total to seven. The Calandra Lark seen in Lincolnshire and The Trumpeter Finch in Devon took their respective British totals to sixteen.

Above: Swallow by Tommy Holden

With a distinct lack of common migrants at south coast watchpoints, observers there had been lamenting the end of spring migration. Nothing could be further from the truth on the east coast; Spurn recorded one of its biggest Swallow days so far this spring, on Wednesday, when 3,356 were counted flying south, along with good numbers of House Martins, this was reflected nationally by the birdtrack reporting rate. It has also been the best week of the spring for Spotted Flycatcher, and wader migration continues apace.

Things should be a little quieter this week as the weather changes and the winds come from the west. However, May is the best month of the year for an American Sparrow to turn up, and with low fronts tracking across the Atlantic, the safe money is on White-throated Sparrow, however, another Lark Sparrow would be very welcome.

Eastern birds arrived on cue

Although the predicted Sociable Plover didn't materialise, a superb 1st summer male Collared Flycatcher did; on the east coast at Holme, Norfolk, scuppering many Sunday evening dinners into the bargain, including mine.

Collared Flycatcher, Richard Thewlis

The conditions are still perfect for migration to continue and some of the highest totals so far this spring of hirundines - Swallows and Martins - were observed this weekend on the south and east coasts. Bee-eaters are still overshooting and were seen at six sites from Devon to the Outer Hebrides, along with at least ten Red-rumped Swallows along the east coast, and one on the Outer Hebrides. Britain's seventh Audouin's Gull turned up at Minsmere, Suffolk.

Audouin's Gull by Dawn Balmer

The first Red-backed Shrikes, classic May birds, were found at the weekend so it won't be long before the first Marsh Warblers are recorded. Tern passage has been impressive both at the coast and inland, where Black Terns are still a feature. With the weather staying pretty much the same for the next few days this weekend could well offer more of the same, and maybe that Sociable Plover will turn up. I'd settle for a Red-footed Falcon in the Brecks though.