Tweets,
A friend sent me this interesting article concerning TREE SWALLOWS and other
birds in the midwest. It appeared in the Milwaukee Journal Sentinel on 29
May 2000.

Bird nesting patterns, ranges are slowly shifting
By Mark Ward
of the Journal Sentinel staff
Last Updated: May 28, 2000

Photo/Gary Porter
Peter Dunn, a biologist with the University of Wisconsin-Milwaukee, holds a
tree swallow. Global warming could prompt swallows to lay more eggs and have
more young, he says, but "it's the interaction among species that's really
unknown."

Town of Saukville - As biologist Peter Dunn walks up a small rise at the
University of Wisconsin-Milwaukee's field station here, the morning
stillness is punctuated by the chattering of tree swallows.

The open field before him is dotted with nesting boxes that Dunn and his
wife and co-researcher, Linda Whittingham, set up some years ago to study
the birds. And on this sunny May day with temperatures edging into the 70s,
there's a lot to see.

Soaring, diving, the small graceful birds, the iridescent blue feathers on
their backs and shoulders glistening in the sun, flit from perch to perch in
a flurry of excitement. It's nesting season, and several clutches of eggs
are almost ready to hatch.

This cycle of life feels timeless, but there's a new rhythm at work here.
Fifty years ago at this location one would have had a hard time finding any
tree swallows this early in the season, let alone nesting couples.

After looking at data from thousands of locations across North America, Dunn
has found that the average date at which tree swallows nest advanced nine
days from 1959 to 1991.

Other studies had found earlier nesting of different species in specific
areas. His was the first to show such a significant change in a single
species across the continent.

Why? Different factors may be in play at different places, but for such a
broad shift Dunn could point to only one major cause: global warming.

Stanley Temple, professor of wildlife ecology at the University of
Wisconsin-Madison, says a similar trend has been seen among many bird
species in Wisconsin.

"Seventy-five years ago, it was rare to see a cardinal in Wisconsin," he
says.

Cardinals, red-bellied woodpeckers and mockingbirds, birds once common only
in the southern United States, are now found throughout the state.

Yet, just as some birds are becoming more common, others are becoming more
rare.

Jeff Price, director of Climate Change Impact Studies at the American Bird
Conservancy in Boulder, Colo., studied warbler species in northern Minnesota
and southern Ontario and found that many are shifting their ranges farther
north. He predicts that over the next century that area will lose 14 warbler
species.

What's still unclear is how this shift in ranges will affect different
species.

"Generalists," such as blue jays and robins, Price says, are likely to
thrive, while "specialists," such as flycatchers and warblers - whose diets
are more limited - are likely to suffer. One study predicts that with
prairie potholes in the Great Plains states drying up, there could be a
reduction of as much as 50% in breeding waterfowl.

Part of the trouble in sorting out the effects of these changes is that so
many variables play a role, Dunn says.

In the case of tree swallows, he says, "we know they're laying earlier.
Typically, when swallows lay earlier, they have more eggs in the nest, and
when birds lay more eggs, they have more young. So, global warming could be
a good thing.

"But we don't know in detail how the food they rely on might change, how
their predators may change in abundance, what's happening on the wintering
grounds. . . . It's the interaction among species that's really unknown."

One thing for certain is that Wisconsin will get a ringside seat. According
to Price, the Great Lakes states - experiencing some significant long-term
warming - are blessed by a broad diversity of plant and animal species.

"Wisconsin is right on the edge where you're going to see everything happen,
" he says.

John Fauber of the Journal Sentinel staff contributed to this story.

Appeared in the Milwaukee Journal Sentinel on May 29, 2000.