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
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.
URI Professor Scott McWilliams (Photo by Michael Salerno) |
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.
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