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While the American elections dominate the news, American birds have also been making our headlines this autumn. Usually just a few species of American songbirds make it here each autumn, but the variety and numbers this year have thrilled birders on the west coast of Ireland, in Cornwall and on the Isles of Scilly.
Two species completely new to Britain and Ireland have turned up, and the excitement in the south-west has been palpable. Our reporter, Chris Sperring, met up with Kester Wilson who has probably discovered the bird of the year and a first for Britain - an Alder Flycatcher. Other notable finds include: the American Buff Bellied Pipit, Red Eyed Viro, American Wigeon and most amazingly the American Nighthawk.
To get a better understanding of what has been happening Brett speaks to lecturer in animal behaviour and author of The Wisdom of Birds, Professor Tim Birkhead from the University of Sheffield.
What are these birds that are going wrong?
Many of them are first migrants and many of them will die. If you go that badly wrong on your migration it’s very hard to get back on course. But we see a very big difference in the abilities to find their way, between the adult birds and first migrants.
How do birds get it right then, how do they know where to go?
It’s a combination of genetic programming, and imprinting, so learning a route by experience. An experiment was done with Starlings that really gives us some insight into this.
About 11,000 Starlings were collected and ringed in the Netherlands, put in cardboard boxes, and flown by plane some few hundred miles east of their normal starting point, to Switzerland, and then set free to migrate. Among these birds, some were adults, others were ‘birds of the year’ that is first-time migrants, baby birds.
In this experiment the aeroplane was performing the role of say a strong wind that would blow them off-course. Of these birds, some were able to find their way to their correct migration destination, in Spain. They were correcting for the distance they had already been flown. And these were the adult birds.
Others went wrong – they failed to realise that they had been displaced and ended up a few hundred miles east of where they should have been. These were the young birds who had never made the journey before. But, when it came to the time to migrate home, they all went back to the correct starting point. So they had ‘imprinted’ that place, and weren’t just relying on their internal navigation. They had to physically recognise it in order to stop there. Later, when they migrated again, the ones that went wrong the first time went wrong again.
So what does this tell us about the way they learn to migrate?
It seems that the birds have a programme, it tells them which way to go and for how far and this is genetic. But if you get a mutant gene, then you might get a bird with the wrong compass setting, or one that flies for the wrong amount of time. But, we also know that the birds don’t rely on their genetic information alone – they are capable of correcting themselves, learning from their environment.
The birds going wrong and turning up in Cornwall are on their own?
Yes. When they go wrong, it tends to be a small proportion. Some birds do fly in family groups, like Geese for example, but for many you just head off on your own. Geese feed differently to many migrating birds, so they fly differently too.
Is this natural selection weeding out the weak?
Yes. Of course if some are genetically mutant, and just head in the wrong direction anyway, then they will probably die out. They are eliminated by natural selection. If you go North instead of South, then you can’t find the food. You die and that’s the end of the line that goes the wrong way.
But we do have examples of the bids going wrong and it working out for the best for them. Say, the Black Caps – a small proportion have gone west by accident on migration, and ended up in Britain, instead of Africa where they were meant to go. And instead of being a disaster for them, it ended up being great. They’d come from Germany, and found that the UK was ok for them, it’s got warmer. And even though they went wrong, they stuck with this new destination – it worked for them, and took them less time to get here. So this is an advantage of what we call advantageous selection.
We heard Kester say the Alder Flycatcher turned up after bad weather – but is weather not really a factor in the birds going wrong?
No – it is an important factor. It can blow birds a certain way so more are likely to end up in Cornwall, Scilly, Ireland for example. And a hurricane off the coast of America can affect what birds and how many we see coming over here too.
We’ve seen a few examples, are there lots of other birds lost over the seas for every one of those that turn up in Cornwall?
Yes. They run out of steam. Millions of them drop into the sea, just totally exhausted. They just run out of fuel. And that’s great for the Gulls, they love all the exhausted migrants. They play with them like cats with mice! So my guess is that the vast majority just die and disappear, and we see just the very few.
Further Reading:
More at Chris Sperring's Blog
Tim Birkhead's book The Wisdom of Birds
All the migrants can be found at Cornish Birding