Jim Lyles wrote:

> On this doggish day in late August, an Associated Press news
> story today reports more evidence that global warming is even
> now affecting populations of things that fly and flutter--in
> this case, butterflies. Below, I'll recap the story.
>
> But if butterflies are already showing effects, I wonder what
> kinds of effects of global warming we may expect to see among
> our new world birds, particularly the more specialized ones.
>
> Does any tweeter care to indulge in wild or even informed
> speculation?

I'm dealing with my 150+ messages in order after 5 days away, so I may be
repeating what's already been thoroughly treated; sorry if I don't add
anything.

Birds aren't as sensitive to temperature changes as insects, so they
probably won't be affected much by slight temperatures changes. What will
change over a longer time period, of course, are the habitats in which the
birds live. In any given area, southern habitats will ultimately extend
farther north and northern habitats retreat. They will do this at a speed
that any bird species can keep up with. Where push will come to shove will
be when habitats come up against natural barriers such as water bodies,
where they will just cease to exist rather than slowly moving north.

What is much more serious is the fact that habitats are patchy in nature.
Smaller patches will probably disappear rather than smoothly retreating
northward, especially trees with their long generation times. In a large,
continuous habitat, the plants at the northern edge of it may be
continually favored while the ones at the southern edge may die out, but in
a lot of situations, other factors will come into play that complicate
this.

Still more serious is the continuing breakup of habitats into smaller and
smaller islands by human activities. This will greatly exacerbate the
deleterious effects of global warming and is, I think, one of the greatest
concerns of environmental biologists. Think of a patch of native forest in
a park with urban/suburban surroundings. As it gets warmer and warmer,
plants that are already near the southern edge of their range will start
dying out. But they won't be replaced by more southerly species (or
individuals), because there are no sources within reach. Multiply this
effect on other plant and animal members of the forest patch and you can
see the problem. Birds are both fairly resistant and motile, but their
habitats won't be.

Dennis Paulson, Director phone 206-756-3798
Slater Museum of Natural History fax 206-756-3352
University of Puget Sound e-mail dpaulson at ups.edu
Tacoma, WA 98416