Migration Mysteries

Our wintering songbirds will soon depart for parts north; one morning, we’ll wake up and they’ll be gone, having flown hundreds of miles through the night while we slept. It’s not until relatively recently that we’ve begun to understand the mysteries of migration. In the 17th century, one outlandish theory that held currency was that the birds flew to the moon for the winter. Aristotle thought that swallows spent the winter buried in mud.

I recently spoke with Rebecca Heisman — author of the new book Flight Paths, about bird migration and the scientists who figured out some of what really goes on — who will be in town on April 19 for a free talk sponsored by the Santa Barbara Audubon Society and the Santa Barbara Public Library.

Just how do nocturnal migrants navigate? Heisman: Birds actually have a number of different ways to navigate, so that if one isn’t feasible on a certain day, they can use other ones. There were really cool experiments done decades ago, where they put birds under planetariums [and] projected the night sky, which could be rotated in different ways. They showed that birds can orient themselves using the stars in the night sky. They can orient themselves using the position of the sun as well, using sunrise and sunset. Some birds have been shown to be able to use the appearance of landmarks on the ground below. And then birds can also sense their magnetic field: They have sort of an internal compass where they can sense magnetic north, so they have a lot of different ways that they can use to figure out where they’re going.

In your book, you clearly lay out the advances in our understanding of bird migration over time, from the results of bird banding all the way to analyzing stable isotopes in bird feathers. Of all the discoveries, which do you think has had the most profound effect on furthering our knowledge of migration?  It’s really hard to pick because different ones have helped in different ways. For example, weather radar lets us look at large-scale migration patterns across the continent that aren’t species-specific but just lets us see what are the really big patterns in terms of migratory movements. And then these tracking devices like GPS and geo-locators help us on the other end of the spectrum to follow the movements of individual birds in great detail.

One of the new things I learned from your book, and which I find fascinating, is that some widespread breeding species in North America, such as the yellow warbler, have distinct geographical populations with particular habitat needs. For example, a warbler nesting in an arid area will migrate south to their wintering grounds in Central or South America and seek out similar habitats. Could you talk about how this was discovered and the implications that this has for bird conservation?  That is one of the things that’s grown out of the Bird Genoscape Project, which is where they are analyzing the genetic differences between populations within a single species, kind of like 23andMe. For birds, just like with humans, there are genetic differences between populations that can tell you something about where their ancestors came from. This is what lets scientists get down to these fine-scale differences and discover how different populations within a species are genetically adapted to make use of different habitats. The reason why this matters is because it has implications for how well these birds will be able to adapt to habitat changes with climate change; we need to understand their habitat needs at both ends of their annual cycle.

I have a sense that in your book, you’re as interested in the people as in the birds. Your book is populated with an array of characters, perhaps none as important as Bill Cochran. Can you talk about his contributions to migration study?  He definitely pops up in more chapters than any other one person. Bill Cochran was basically the father of wildlife telemetry, not just for birds, but for all animals. So when they put radio transmitters on animals to follow their movements, he was the first person that figured out how to do that in a way that was practical. This work got started back in the ’60s and was related to the launch of Sputnik. If you’re going to put a radio transmitter on a bird, one transmitter only has a range of a few miles. So if you want to be able to follow a bird that’s migrating long distances using one of these transmitters, you have to follow the bird to stay within range. So he would use small planes to follow birds, and also station wagons with radio receivers sticking out of a hole in the roof, to follow cross-country for long distances, and he had some really amazing adventures.

Do you think methods of figuring out the mysteries of bird migrations have gone as far as they can go, or can you foresee something new coming along in the future?  Certainly the genetic methods are getting better and better all the time. The transmitters are getting better. They’re always building smaller and lighter ones with longer battery life. The cutting edge of migration research right now is called migratory connectivity, which is getting down to this really fine scale with specific populations within a species. Do they take different migratory routes? Do they use different stopovers? Do they use different wintering grounds? Because we really, really need to get down to that really fine level of detail to be able to pinpoint where the problems are that are causing migratory species to decline and figure out how to ensure that conservation efforts are actually effective.

Do you hold out much hope that this work can reverse bird loss?  If you look at the data out there, the prospects are not great. We know that there are about three billion fewer birds in North America now than there were in 1970, which is almost a 30 percent decline, which is just staggering. And so it’s definitely hard to feel optimistic sometimes. But I was a little bit surprised that when I went to the conclusion of my book, I called two people who were leading large migratory bird conservation efforts, and they both really insisted that they do feel hopeful. It sounded a little bit like that was a willful choice, like they were choosing to feel hopeful, because otherwise, how would you be able to get up and go to work every day if that was your job? But I think you can look at large-scale environmental problems that we’ve come together to maybe not completely solve, but mitigate quite a bit in the past, like the hole in the ozone layer. Acid rain is something that you heard a lot about a while ago, and you don’t hear about that problem as much now. That’s because these problems have actually gotten better. And so I think that there is still hope that we’ll be able to maybe not completely reverse some of these declines, but at least help them as we get this better data to better figure out where exactly the problems are that we need to fix.

The public is welcome to attend a free talk with Rebecca Heisman, author of Flight Paths, Wednesday, April 19, at 7:30 p.m. in the Faulkner Gallery of Santa Barbara Central Library (40 E. Anapamu St.). Books will be available for purchase and signing, courtesy of Chaucer’s Books.