Bird Feeders Speed Up Evolution, May Split Species

Reporting in Current Biology, researchers write of a warbler that has quickly evolved an unorthodox migration path to England to take advantage of backyard bird feeders. Study author Martin Schaefer explains how the clever migrants could become a distinct warbler species.

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JOE PALCA, host:

This is SCIENCE FRIDAY from NPR News. I'm Joe Palca. Ira Flatow is away.

If you've ever studied evolution, you've no doubt heard of Darwin's finches, a handful of related bird species he collected in the Galapagos. It turns out that the birds all came from a common ancestor, but through the years, one generation after another, the birds' beaks began to change into all sorts of shapes and sizes - pointy ones, stubby ones, slender ones - to take advantage of different conditions and foods on the different islands.

Eventually the finches developed into distinct species adapting to fit their particular environmental niche. But evolution didn't stop with Darwin. Modern birds are just as ready to evolve if they find a new food source, and it looks like at least one species of birds has been doing that today. It's evolving to take advantage of all the bird foods set out in feeders in England over the winter.

My next guest has been tracking the changes of these species, a small warbler called a Black Cap. His research appears in the journal Current Biology. Martin Schaefer is the author of that article in Current Biology. He is an associate professor of evolutionary biology at the University of Freiberg in Germany. He joins us over the phone. Welcome to SCIENCE FRIDAY, Dr. Schaefer.

Dr. MARTIN SCHAEFER (University of Freiberg): Hello, thank you very much.

PALCA: And I want to invite the audience to join us, our conversation about the Black Caps. The number is 800-989-8255, that's 800-989-TALK. If you're on Twitter, you can tweet us with your question by writing the @ sign, followed by scifri. And if you want more information about what we we'll be talking about this hour, go to our Web site, www.sciencfriday.com, where you'll find links to our topic.

So Dr. Schaefer, tell us about these birds. When did they start migrating to England and was that normal for them or did they decide they'd like to go have the bird food in England?

(Soundbite of laughter)

Dr. SCHAEFER: Well, the birds started to migrate first to England in the 1960s. So it's about 50 years ago. And traditionally they go to the warmer areas in the western Mediterranean area that is mainly Spain. And obviously, the birds didn't know they're going to be fed in England. But what happened is that the eventual bird turned up in England and found a very good food supply there, and because of this species we know that the migratory orientation is genetically termed. It gave that migratory route to its offspring, which also then migrated to England and survived (unintelligible) the winter owing to the bird food.

PALCA: I see. So just to be clear, these are birds that normally live in the summer in Germany.

Dr. SCHAEFER: Right.

PALCA: And in the winter they fly to southern Europe where it's warmer, but some of them, for reasons best known to themselves, flew north and found themselves in England.

Dr. SCHAEFER: Yeah.

PALCA: Go ahead.

Dr. SCHAEFER: Yeah, that's even getting a more complex story because now we even find some birds that go as far north as Iceland and over winter in Reykjavik City, where they're also fed. So it's an extremely strange behavior if you look at it from an ecological perspective, because the birds are migrating far north to move into there.

PALCA: So what has changed, I mean, is it - I guess the other question, which I guess you've to establish, is that some birds now always fly north to England and some birds typically fly south to Spain and they don't mix, in other words. They go there separate ways when it's time to migrate.

Dr. SCHAEFER: Yes, that is probably the most significant and important result that we have because it shows that reproductive isolation - the barrier to interbreeding freely evolves very quickly within only 50 years. So that is actually evolution that you can witness in the timeframe.

PALCA: But that's what I was going to say. Is it the thought that - that - I mean, let's say that instead of finding bird feeders in England, these birds had just flown north for some reason and found a hot spring that existed for some reason and where there was a lot of fruit available in the wintertime, would that have had the same affect? Is it specific to the human intervention or is it just that something positive happened in the environment and then over 50 years they were able to change enough to take advantage of it?

Dr. SCHAEFER: Yeah. It's the latter point. If something positive happen in the environment and it was consistent enough over the years, so that the evolution of this new migratory root could actually be stimulated. So it's not - as you say, it's not particular to the human action, however it is, I think, one of the convincing ways that we humans do change the environment. And in this case it's actually good news because the Black Cap is plastic enough, in evolutionary terms, to adapt very quickly to these changes that we - with which we influence (unintelligible)

PALCA: Okay. And Black Cap, again, is - it's a warbler, right?

Dr. SCHAEFER: Right. It's a small warbler similar to the wood warblers you have in the U.S., but it is not as colorful.

PALCA: Okay. We won't that against you. All right, well, let's take a call now and go to Tom) in Grand Rapids, Michigan. Tom, welcome to SCIENCE FRIDAY. You're on the air.

TOM (Caller): Hey, thank you. How are you doing?

PALCA: Good.

TOM: Good. I got a quick question. I was just kind of curious. You know, most of the (unintelligible) suggests that it will actually take millions of years for significant evolutional changes. And I'm wondering how in your study of, you know, just a few decades and a few generation you can already mark such differences and claim that as, you know, physiological evolution?

PALCA: Interesting.

TOM: I'll take my answer off the air.

PALCA: Okay. Thanks, Tom, very much.

Dr. SCHAEFER: Yeah. It's a very good question. It is mainly that the Black Cap has a very large genetic variation for migratory traits. That means there is a lot of genetic variation in how far the birds go, in which direction they go and because there is so much variation, we have the raw material for selection to act upon this variation and for evolution to be relatively quick. And when we started the project, I mean, we obviously didn't know that we're going to find that the reproductive isolation will evolve that quickly in that bird species. However, once it evolved, there is an even higher possibility for adaption and for evolution to occur because all the adaptions towards a specific migratory root such as the one towards the U.K. will not be lost due to recombination with birds migrating in another direction.

PALCA: I see. Go ahead. No, I was just going to - I was going to ask the question, if you looked at two of the these birds side by side, the ones that typically went to England now, and the ones that went to Spain, do they look different?

Dr. SCHAEFER: No, they still look very much the same. So what we need to do is we analyze their claw material that is equivalent to our fingernails and we - by analyzing the claw material we can pinpoint in which area they spent the winter. So wee don't have to envision evolution, in this case, as producing, say, a new species within only 50 years. No, it's going to take considerably longer than that.

PALCA: I see. So it's not as if their beaks are changing shape.

Dr. SCHAEFER: Yes. The beaks are changing their shape and also the wings are changing their shape, but the changes are relatively small, similar as in the examples of the Darwin finches that you alluded to in the beginning. It's in the range of, say, one to two millimeters. So we have to measure them very well and accurately to actually pinpoint the differences.

PALCA: Uh-huh. And - okay, so you're seeing these small physiological changes or small anatomical changes. Do you see genetic changes between the ones that migrate in one direction versus the ones that migrate in a different direction?

Dr. SCHAEFER: Yes. We also see these genetic changes and we see them in genetic material that is not (unintelligible) for particular traits. And this is important because this genetic material is providing the kind of baseline of genetic changes. So we find the - that they are genetically distinct and we find that they are morphologically distinct, and even though we are only talking about the range of one or two millimeters, this is ecologically important.

PALCA: Right. So - but the question, I'm wondering, then is, these non - the changes that you're seeing are not in the genes, but how they're switched on and off, is what I understand these non�regulatory segments are all about - or these non-coding segments are all about.

Dr. SCHAEFER: Yeah. They are important because they are very polymorphic. And�

PALCA: What does that mean, polymorphic?

Dr. SCHAEFER: That there is a lot of variation in these non-coding gene areas and they mutate rather quickly. So if you are to see changes that you - where you - no, let me put it another way.

PALCA: Okay.

Dr. SCHAEFER: If you look at reproductive isolation, you will have a buildup of genetic changes if two populations are not freely interbreeding. And this is what we look at if we look at these non-coding areas because they mutate very frequently. It's easier to detect changes here.

PALCA: Right.

Dr. SCHAEFER: And so the changes we find between the two populations are still relatively small, but they are significant and they exceed, say, the genetic difference of blackcap populations that are separated by 800 kilometers from southern to northern Germany.

PALCA: So if this process went on for many more generations, do you think you'd have two different species of blackcap?

Dr. SCHAEFER: Yes, if this same process is continuing, then we would eventually end up with different species because what we are seeing now is this kind of first step in inter-speciation. However, it depends obviously on a number of assumptions, say, that the English are still feeding the birds for a long time to come and are not kind of put off feeding birds because of an economic crisis or whatsoever.

So we can't really say at this stage that it's going to be speciation. The process is still reversible, but nevertheless, you are right. It's the first step towards speciation.

PALCA: Right. So, I mean, I guess this is a question, but does this mean that people should think twice before they feed birds because they're having an influence on evolution?

Dr. SCHAEFER: Well, let me put it slightly different. I don't think it's a bad thing. Feeding birds is not a bad thing, and in this particular case, the blackcap is actually benefiting very much from the situation because it found a new migratory area that is not that far away from their breeding grounds in southern Germany and Spain. However, I do think that we should be better aware of the changes that we are actually producing in the species that surround us. For example, if we are feeding a lot of chickadees in winter and they survive very well throughout the winter, these birds will occupy nest cavities that other long-distance migrants might need. And they will be kind of at a disadvantage relative to the competition of more chickadees because fewer of them died over the winter.

PALCA: I got it. So you could be having a significant effect on the ecosystem by feeding the birds.

Dr. SCHAEFER: Yeah, yeah.

PALCA: Okay. All right, well, that's all the time we have, I'm afraid. Thank you very much for joining me today.

Dr. SCHAEFER: Thank you very much for calling.

PALCA: Martin Schaefer is an associate professor of evolutionary biology at the University of Freiburg in Germany.

This is SCIENCE FRIDAY from NPR News.

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