Wednesday, March 21, 2018

How birds get from there to here

Robins have already returned to southern New England from their wintering grounds to the south, and soon many millions of other birds — warblers, orioles, swallows, vireos, flycatchers and others — will follow suit. Scott McWilliams, a professor in the Department of Natural Resources Science at the University of Rhode Island, has been curious about bird migration since his childhood in Ohio. He chose to work at URI in part because of its proximity to Block Island, where bird migration
URI Professor Scott McWilliams (Photo by Michael Salerno)
research has been conducted for many years. For more than two decades, McWilliams has studied the physiological changes that birds undergo as they prepare for migration, especially the changes to their digestive system.

How did you get interested in birds?
When I was growing up, I was always fascinated with seasonal changes, and the birds leaving for the winter and coming back in spring were something that really caught my attention. We were surrounded by Amish families, and they had German-Dutch names for all the birds, so I got to learn two or three different names for every species. They knew a heck of a lot about the natural history of the birds, too. Birds were a good talking point with them, and also one of those fascinating things about the harbingers of spring and fall.

What’s the most interesting thing about birds?
The answer depends on who you’re talking to. What I do know is that people are fascinated by birds. Birds are in our backyards and around us, there’s tremendous variety in terms of colors and behaviors, and many of the species have adapted to be around people so they make it impossible for us to ignore them. For me as a scientist, I really like the idea of studying dinosaurs that live with us today. Essentially, they are the remnants of the dinosaur era that have made it successfully despite the dinosaur’s decline. They occur on every continent on the globe, so they are a tremendous example of adaptation and acclimation to various environments.

How do you describe the research you do?
I study birds that migrate and how they interact with their environment and how what we do impacts their life.

What is it about Block Island that’s notable to migrating birds?
The geography of southern New England is such that we have mostly an East-West Coast, with Block Island about 20 kilometers off that coast. Block Island has always been a place where tens of thousands of migrating songbirds end up each fall as they travel south. It allows you to study how the birds’ migration directly interacts with the quality of the environment and the weather patterns that occur. And if you look at the population dynamics of most any songbird, most mortality occurs in the first year during fall migration, so decisions that birds make during that time have much larger consequences for the population of those particular species.

Why do birds migrate in the first place?
Birds that migrate live in seasonal environments, so they’re primarily migrating to get to places during especially cold periods of the annual cycle when it’s too cold and they can make a better living elsewhere. All the birds that migrate have evolved to migrate in part to respond to the seasonality of the environment.

But not all birds migrate. Why not?
Some have decided to weather the storm, so to speak. Many of those species that are resident here do so because they can tolerate really cold temperatures; they’ve evolved an ability to deal with the cold. It’s a minority of species. The vast majority of species do some sort of migration to avoid seasonal declines in temperature or food resources.

How do they know when it’s time to migrate?
I love to think about these kinds of things. Almost all species use the environmental cue of photoperiod [daylight length] as a way to tell them when migration should occur. We can put birds in captivity and isolate them from the environment and just change the light schedule, and we can put them into a migration state — they start jumping around at night, they start fattening up, they start eating lots more. Photoperiod is the environmental cue that underlies the migration tendencies of birds. It tells you when spring happens, when fall happens. But almost all birds also use other cues, like weather patterns. Photoperiod defines the window of opportunity of when you’re going to migrate, but then you use weather and other environmental cues to decide exactly the day and time when you’re going to move.

How do they know what direction to go and when they’ve arrived at their destination?
It’s in their genes. The birds actually migrate for a certain number of days, and that certain number of days is what we call endogenously encoded. The genes they’ve inherited tell them that migration is roughly 40 to 50 days or it’s 20 to 30 days or whatever. There’s a migratory restlessness period that you can define in captivity – they’ll be restless for a certain number of days and then they’ll just shut it off. That tells them the duration. The direction is also coded for most songbirds in their genes. But there are other migration strategies as well. Cranes and geese, for example, learn where to go by following their parents.

What does it take for birds to prepare for migration? Like physiological changes?
Migration takes guts.

What do you mean by that?
Birds have a part of their brain that detects light levels and tells their brain what the photoperiod is. When that happens, there are brain hormonal responses that basically tell the bird it’s time to eat more, and they will increase how much they eat by two, three, four times on a daily basis, and so they start to fatten. Most birds use the amount of fat as their own internal indicator as to whether they are ready to migrate. Then, if it’s warm and the winds are favorable, they’ll take off and burn some of that fuel. Then they’ll end up at a stopover site somewhere and do it again.

What do you mean when you say that migration takes guts?
If you or I were going to run a marathon, the last thing we’d want to do is begin by getting really fat. Our digestive system won’t allow that, we’ll get too full, and that’s true of birds, too. Birds have evolved this incredible flexibility in their digestive system. When the hormones come from their brain in response to the photoperiod that tells them to start eating more, their digestive system responds by increasing in size by three or four times over the course of a couple days. Then they’re able to consume lots more and convert it to fuel. When they migrate, they may fly for several days and not eat at all. They basically reduce the size and the function of those digestive organs during that time, and then once they land, they have to build it back up. They’ve evolved this tremendous flexibility in their digestive system to accommodate this alternating feeding and fasting period.

What else is interesting about bird physiology?
A lot, especially the physiology of those that stay here for the winter. They have some incredible adaptations, like how ducks can stand on ice and still keep their feet warm, or how tiny songbirds can stay warm on very cold winter nights. They’re pretty amazing creatures.

This article first appeared in the Newport Mercury on March 20, 2018.

No comments:

Post a Comment