British birds’ beaks may be evolving in response to birdfeeders

Great tits in the UK, where birdfeeders are common, have developed longer beaks than their Dutch counterparts.

Over 150 years after Darwin’s observations of Galapagos finches, birds’ beaks are still capturing the attention of genetics researchers. In a new Science study, scientists have for the first time identified genetic differences between great tits in the UK and the Netherlands, and linked these genetic variants to longer beak lengths in the UK. The short timeframe for these changes—British great tits had shorter beaks than they do today as recently as the 1970s— points to the relatively recent proliferation of garden birdfeeders as a likely factor. We spoke with Mirte Bosse, one of the paper’s lead authors, to learn more.

ResearchGate: Why compare the DNA of British and Dutch birds?

Mirte Bosse: European great tits are thought to all belong to a large population with relatively little differentiation. Interestingly, UK great tits already had a status as sub-species based on differences in their form decades ago. We were interested to know whether we could find some genetic differences between the Dutch and British great tits, and whether these differences were localized in certain parts of the genome. The fact that genes involved in face and beak shape were over-represented in these highly divergent parts of the genome led us to investigate these traits further.

RG: Over what timeframe did the difference in beak length emerge?

Bosse: Based on our analyses from museum samples, we know that the difference has been there for at least decades, and if we look at the rate of change we would suggest it started a bit over a century ago. Our study of a 25-year time span demonstrates that bills in the UK have gotten bigger over these recent years as well.

RG: Why do you think British great tits have developed longer beaks than their Dutch counterparts?

Bosse: We know that supplementary feeding with birdfeeders is huge in the UK compared to mainland Europe. So we decided to analyze the propensity of the birds to visit feeders in an experimental setting. Interestingly, the birds with longer bills visited the feeders more often, suggesting they are better adapted to the feeders.

RG: Could there be another explanation besides birdfeeders?

Bosse: We still have a lot of open questions about the mechanisms. Different competitors, type of song, behavior, or an alternative food source could play a role as well. But based on our study we assume supplementary feeding plays a role. We are thrilled to look into the reason for this rapid adaptation in the near future.

RG: Why would a long beak be an advantage at a birdfeeder?

Bosse: To determine this, we’d first need to know whether bird feeders have had the same design since the birds started using them. For the directional selection to happen, they should not have changed much over time. Then we need to find out what it is that gives birds with longer beaks an advantage at the feeder sites during winter, and how this results in more fledglings in spring. This is an intriguing question we can only speculate on now. We hope to answer it in future studies.

RG: If birdfeeders are behind the difference, what do you think would happen if everyone in the UK stopped using birdfeeders tomorrow? Would long-beaked birds be at a disadvantage?

Bosse: Well, given the massive amount currently spent on bird feed, I don't see that happening!  But if it did, great tits would have to find an alternative food source during winter. It’s questionable whether those with longer beaks would have the same advantage under those conditions—but who knows?

Featured image courtesy of Sigurd Rage