In England there are a lot of bird feeders….a lot of them. So many that a significant number of Blackcaps winter in England rather than their usual haunt, Spain, and more of them are surviving the harsher winters because of access to food.
European birds called blackcaps follow a different “evolutionary path” if they spend the winter eating food put out for them in UK gardens.
The birds’ natural wintering ground is southern Spain, where they feed on the fruits that grow there.
Researchers describe the impact this well-intentioned activity has had on the birds in Current Biology journal.
So, these birds are surviving and are reaching their breeding grounds considerably sooner than their Spanish kin. Also, birds that winter together tend to mate with each other. This is a perfect set-up for species differentiation. The British birds are mating with other British birds, while the Spanish group mates with other Spanish birds. Given enough time, these two groups may end up being two different species.
Dr Martin Schaefer from the University of Freiburg in Germany led the research.
He and his team found that blackcaps that migrated to the UK for the winter were in the very earliest stages of forming a new species.
He explained that some blackcaps (Sylvia atricapilla) would always have migrated “a little further north” than others and eventually “ended up in Britain in the winter”.
It’s positive news for us, because it means not all the changes [humans] produce are necessarily bad
Martin Schaefer, University of Freiburg
“But those birds would have had nothing to eat,” he said.
It was when garden bird feeders became more popular in the UK, that an evolutionary division began to emerge.
“As soon as the British provided a lot of bird food, those birds would have had a much higher probability of surviving the winter.”
And because the UK is closer to their breeding ground, those birds would also have returned earlier to claim the best territory
The researchers, from Germany and Canada, set out to discover if the birds that spent the winter availing themselves of garden bird-feeders were in fact a distinct group.
To do this, they studied the blackcaps at a breeding ground in Germany.
The team were able to use a chemical “signature” from the birds’ claws to identify where they spent the winter, and what food they ate.
“Then we took blood samples and analysed those to assess whether… we had two distinct populations. And that’s exactly what we found,” said Dr Schaefer.
“To a very large extent the birds only mate [with] birds with the same overwintering grounds as them.”
This initial “reproductive isolation”, Dr Schaefer explained, is the very first step in the evolution of a new species.
“This tells us that by feeding birds in winter we… produce an evolutionary split. And we have produced these initial steps in as little as 50 years.”
So, apparently we have forced an evolutionary change. A tad scary perhaps, but rather exciting as well.
The rest of the article at BBC.