Autumn bird migration news: Still plenty to come
Each week Paul and Nick from the BTO are updating us on all the comings and goings of autumn's bird migration. We'd love to hear what you've been seeing too, whether in your garden or out and about.
The first waxwings are here © John Harding/BTO
As the migration of our summer visitors comes to a close, it's easy to think that autumn migration also comes to a close. Nothing could be further from the truth. Migration watchers in early November can be rewarded with some of the most spectacular bird migrations of the year.
At this time of the year migration is very much influenced by the weather in northern and eastern Europe, with temperature all important.
Falling temperatures on the continent will mean an influx of golden plover © Tommy Holden/BTO
A sudden freeze will see berry crops fall and waterbodies ice over, prompting cold-weather movements for thrushes (redwings, fieldfares, blackbirds, song thrushes and ring ouzel), finches (siskins, redpolls, linnets, chaffinches and bramblings), larks (skylarks and woodlarks), pigeons (woodpigeons and stock doves) and wildfowl (ducks, swans and geese).
So far this autumn with temperatures higher than normal we have seen very little of this. The daytime temperature in eastern Europe, however, is forecast to drop to near freezing this weekend, so we could see an arrival of pochard and goldeneye, along with a small arrival of Bewick's swans. [Editor's note: Slimbridge, Autumnwatch's hosts for the next four weeks, is one of the UK's best sites for Bewick's.]
Up until now there hasn't been a need for these birds to move. Check out the BirdTrack reporting rate for goldeneye.
Any cool crisp day with light winds, particularly from the east, over the next couple of weeks should prompt a big movement of woodpigeons, with flocks often tens of thousands strong heading south-west. You don't have to be on the coast to observe this migration spectacle, big flocks can be seen flying over land-locked counties too.
A sudden freeze will see blackbirds on their way © John Harding/BTO
The first waxwings of the autumn have been seen, with a flock of 20 birds being found in Stromness, Orkney, and three seen on Lewis, Outer Hebrides. It's too early to say whether it will be a waxwing winter, but with the drop in temperature on the continent this weekend we might see a few more arrive. At this time of the year waxwings generally arrive in the north and work their way south as berries become harder to find.
Flocks of lapwings and golden plovers on the move are a sure sign that the ground is frozen on the continent, so falling temperatures there could cause an influx of these winter field inhabiting waders.
Question of the week: Is it true that some birds reduce internal organs to compensate for the extra fat they carry for migration?
This is absolutely true and is illustrated perfectly in a passage from Ian Newton's excellent book, Bird Migration. Organ reduction has been found in a number of migratory species, including pied flycatchers, willow warblers and swallows. However, extreme changes were found in bar-tailed godwits killed accidentally in Alaska as they hit a radio tower, just after take-off on a presumed trans-Pacific flight of at least 10,400km to New Zealand.
These Alaskan godwits had some of the highest fat contents recorded among birds, comprising 55 percent of total body mass. They also had relatively large breast muscles and heart (exercise organs), but very small gizzard, liver, kidney and gut (digestive organs). They had largely dispensed with parts of their metabolic machinery that were not essential during flight, presumably converting them to other tissue.
On arrival at their migratory destinations, birds rebuild their digestive organs, so that they can once again feed efficiently.