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PRI's Environmental News Magazine

Vanishing Migratory Birds

Air Date: Week of June 28, 1996

Several familiar songbird species have seen their numbers dying off in recent years. While their wintering grounds in South and Central America have been disrupted, so have their northern breeding grounds, and possibly many areas along the flyway. Scientists are studying the likely causes in a new study of New England's Connecticut River Valley. Tatiana Schreiber reports.

Transcript

CURWOOD: The numbers of many songbirds have been falling for some time, including some warblers, verios, thrushes, flycatchers, and sparrows. Scientists blame disruption of their wintering grounds in Central and South America and their breeding grounds in the north, but they also suspect that conditions are changing along the flyways between the two. There are many questions about the changing ecology of these migration routes, and as Tatiana Schreiber reports, a new study of New England's Connecticut River Valley hopes to answer some of them.

(Bird song)

SCHREIBER: It's about 4 in the morning. The birds we're hearing now are right outside my house in southern Vermont. I'm awake this early because I'm meeting a biologist from the Vermont Institute of Natural Science about 60 miles up the Connecticut River.

(Bird song continues. Fade to gear being moved and a zipper being pulled.)

McFARLAND: The ten points are about 200 meters apart, straight line down the river, so --

SCHREIBER: That's Kent McFarland, a self-described bird geek, one of dozens of professionals and volunteers involved in the Migratory Bird Stopover Habitat Survey.

McFARLAND: Ninety percent of the birds I detect are by ear, you know, we're not going to see very many at all. We're going to be hearing most everything. Which is good for radio. (Laughs)

(Footfalls on brush)

SCHREIBER: The survey is a 3-year project looking at the resources neo-tropical birds need during migration. Other studies have shown that deforestation, forest fragmentation, and pesticides have harmed birds on their wintering grounds in South and Central America and their breeding grounds in the north. This study will help determine the importance of the Connecticut River Valley as a migratory flyway between the two.

McFARLAND: Because these birds are flying a hell of a long ways, and they have to stop at key areas and refuel. If they're not able to do that, they're not going to make it. And so, you know, it's not only the breeding ground and their wintering site, but it's also in between.

(Water flows; birds sing)

SCHREIBER: Study participants will survey birds at hundreds of count sites in Connecticut, Massachusetts, New Hampshire, and Vermont, over 5 weeks each spring. The count sites are located throughout the watershed.

McFARLAND: A lot of these birds are after insects, and most of the insects are eating the leaves. So I'm thinking they'll probably follow the tree phenology right up the Connecticut, up the tributaries and into the highlands.

(Footfalls on brush)

SCHREIBER: Blue flags mark the points where McFarland settles in to focus on birdcalls and songs.

McFARLAND: (whispering) What I'm doing is I'm just noting every bird minute by minute for 10 minutes. Um -- and I just note whether it was in, out, or flying over my imaginary 50- meter circle.

SCHREIBER: McFarland points out a red-eyed verio foraging in an oak tree.

(Bird songs)

McFARLAND: Back from the Amazon basin.

SCHREIBER: Really?

McFARLAND: Yeah.

SCHREIBER: When did it come back?

McFARLAND: Oh, it showed up, oh, 3 weeks ago maybe.

SCHREIBER: This is the last of the spring migration counts. One more count this summer will assess how the number of breeding birds compares to the numbers that flew through during migration.

(Bird songs)

McFARLAND: That's a cool bird. That's a very cool bird, great-crested flycatcher.

(Bird song continues)

SCHREIBER: Loud.

As McFarland notes down a great-crested flycatcher, I try to figure out how he knows he's not hearing the same bird twice. He says that's the art to the science. By listening closely he can distinguish individual birds by their movements.

McFARLAND: Now that nuthatch that we heard over there, it slowly traveled. I was listening to it and now its right above us.

SCHREIBER: But if there's any doubt, he says, leave it out. It's a judgment call.

(Birdcalls continue)

McFARLAND: You know chickadee? They're all phoe-beee. (A chickadee calls.) Hear it? There's also a king bird, but its way, its probably across the river. (A robin calls.) Oop - - robin. (The robin calls again.) A peewee way out there. Eastern wood peewee, which is nicely named because they actually say pee-wee. Of course they do that to every bird.

SCHREIBER: McFarland points out that with farmland, roads, power lines and development, it was a challenge to find sufficient areas of uninterrupted hardwood forest in which to conduct the study. This fragmentation of the forest is also the reason some songbirds are in trouble in the first place. The edge between forest and field is prime habitat for bird predators like raccoons and possums, and its attractive to certain birds.

McFARLAND: Chestnut-sided warblers, you know, back in Audubon's day, were very, very, very rare. He saw very few chestnut-sided warblers. Now, I mean, around here, you can't swing a stick without hitting one. So -- (laughs) you know, that's because all the edge, because they love the edge.

SCHREIBER: Right.

McFARLAND: We're actually going to jump this fence.

SCHREIBER: Oh.

MC FARLAND: It gets tricky in a couple of places. But things like wood thrushes on the other hand can, have been shown to be sometimes artificially attracted to the edge, and consequently that's where the cowbirds are and so they've been really heavily hit by cowbirds in many areas. And they're really declining quite rapidly.

SCHREIBER: McFarland says brown-headed cowbirds prefer edge habitat and are expanding in the east, crowding out other birds.

McFARLAND: Wood thrushes are in a heap of trouble. Enjoy the song while you can because it's going fast.

SCHREIBER: We didn't hear any wood thrushes on our walk.

(Footfalls)

SCHREIBER: The migratory bird study is taking place within a new fish and wildlife refuge encompassing the length of the Connecticut River 420 miles from Canada to Long Island Sound. McFarland says the broad area covered by the refuge and the survey is vital because what happens in one part of the watershed affects every other part.

McFARLAND: This spring, since there was a cold spell, the birds got dammed up in Connecticut, it seems, for a little while, and kind of hung out there. And then they moved on up here to Vermont. So if there's no habitat in Connecticut for them to hang out while the weather got better farther north, then they wouldn't be coming farther north, because they wouldn't exist.

SCHREIBER: The refuge, named for late Massachusetts Congressman Sylvio Conti, is unusual in that it includes not only wild areas but human habitat: cities, roads, and industry. The idea is to find ways to balance the needs of humans and other species.

SCHREIBER: Do you think it's a workable concept?

McFARLAND: Hmm. It has to be. (Laughs) Or we're in big trouble. If you kick around in the woods a lot as a biologist, you see some pretty devastating effects going on with things, from frogs on up to birds and butterflies. That things are, things are getting hammered by humanity, and eventually it climbs its way up and its humanity that's going to get hammered.

SCHREIBER: Like the cautious biologist he is, McFarland won't speculate on what he's noticed so far, since comparative data won't be available for 2 more years. At that point study leaders will sit down with the Fish and Wildlife Service and recommend ways to preserve biological integrity in the area. The most likely recommendation is that mature woodland along the river valley should be protected as critical habitat for migrants.

(Bird calls)

SCHREIBER: For Living on Earth I'm Tatiana Schreiber in Norwich, Vermont.

 

 

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