Climate Change And Migrating Birds

Chris - Right now we're going to talk to Marcel Visser who's at the Netherlands Institute of Ecology. He's going to talk to us about how climate change is having a fairly major impact on animals that migrate and how they then reproduce. Tell us about your research and how you went about studying this problem.

Marcel - Well we have studied migratory birds in the Netherlands for a long time and one thing we noticed at one point is that the birds are coming in earlier. They were also laying earlier. The pied flycatcher, which comes over from Africa, seemed to be laying its eggs very quickly. In the old days it used to be two to three weeks between arrival and laying, and now it is only a week.

Chris - So birds are leaving Africa, they're leaving according to when they think it's the right time to come back, they're arriving but they're arriving at a time when the seasons have already moved on.

Marcel - Yes, it's very difficult for the birds to predict the conditions when they are all the way over in Africa. The birds use some cue like day length or an internal clock and it used to work very well. But now, by the time they come back, spring has already advanced there quite a bit and it's too late to really take advantage of all the food that's around. There's only a very short period where food is around in the forest, and this is quite important to realise. There's only about two or three weeks where there are a lot of caterpillars around to feed the chicks.

Chris - So how badly are the birds being affected and is this something we can actually do something about?

Marcel - Well in the case of the pied flycatcher we know that the majority of the birds now have their nestlings in the nest too late. We know that by the time they start feeding the nestlings caterpillars, the caterpillars are already on the decline. The other things we have shown is that there are different areas within the Netherlands and some of these areas have a very early food peak, the birds breed early, the caterpillars breed early and everything is early. In other areas, especially where there is poor soil, the peak is a bit later. It is clear that the pied flycatchers in these early areas are really too late, and you can see here that they are declining. The numbers are dropping and in some of these areas the flycatchers have completely disappeared. In the other areas, the poor areas, where food is late, they just arrive on time to raise their offspring and they're just about hanging on. So they're not declining there. It's a very clear effect on population numbers.

Chris - Do you think that this is going to be confined to this species of bird or are other migratory birds other than pied flycatchers likely to be affected?

Marcel - I think it's a very general pattern, especially for the long distance migrants and the ones that come from Africa because they have no idea how things are changing here. The solution, if you ask me what we can do about it, is to reduce the increase in temperatures. That's the only thing we can do.

Chris - It's not really a short term solution though. This is a couple of hundred years of carbon dioxide pollution and if we try and stop it now, it might not be in a do-able amount of time.

Marcel - If we now reduce our CO2 output by 60% and the increase in temperature will still be two degrees in the next 100 years, that is something we can't do anything about. But if we keep going on like we do now, it will be nine degrees, and that's not a trivial difference for the birds. What will happen with these pied flycatchers is that we will see natural selection. The birds that arrive early will get most offspring and these offspring will also arrive earlier as we know that this is heritable. So there is some scope for adaptation in the birds, but the rate of adaptation will be slow. So if we can keep the increase in temperature at a reasonable level, the birds will probably be able to follow that. But if we carry on the way we are going, then the increase in temperature will be so rapid that there is no way that the birds can keep up.

Chris - So are these birds able to adapt to climate change?

Marcel - Well that's actually the thing we're looking at in close detail now. We're looking at the kind of selection there is and the kind of heritability there is. What we can estimate now is that they will be able to evolve in time but it critically depends on how fast the climate is going to change. It's down to the rate of evolution in these birds and the rate that we impose on them.