Mike Smith made some really good points in his commentary about Neotropical
migrants. My opinion is that the "problem" boils down to this. Not that
many years ago, someone came up with the thought that bird population
declines could be caused by destruction of wintering habitat (of those
species that are migratory). Right away people started pointing fingers at
our southern neighbors to stop destroying their forests. I think this is
called the "we've gotta have a scapegoat" syndrome. Similarly, with
relatively little evidence, the thought developed that all these birds (now
"Neotropical migrants") were going down the tube, and this bred a kind of
hysteria (the "freak out when you find out" syndrome). Unfortunately, the
hysteria (or "concern" if you want to be kinder and gentler) quickly
outpaced the level of knowledge. The latter has caught up to some extent,
and we now know that (1) numerous species of birds that breed in North
America have decreased over time, and (2) many of them are species that
winter in the Neotropics. We also know that (1) many Neotropical migrants
have not decreased over time, and (2) there is just as much, if not more,
likelihood that changes on the breeding grounds have caused these
decreases.

Changes on the breeding grounds that are probably most important are
habitat changes, in particular forest fragmentation that changes forest
ecology and microclimates and allows predators and brood parasites
(cowbirds) and perhaps competitors more access to forest-interior species,
many of which appear to be declining. Resident species may be able to use
forest patches smaller than those that are adequate to migrants.

Almost all the quantified data so far are from the East, where this really
seems a serious problem. Information from the West is more equivocal,
although some species have declined in the only quantitatively valid
assessments done so far, those of breeding-bird survey routes. They paint
divergent pictures at times--for example, species declining in Oregon but
increasing in Washington, or vice versa. There may be valid reasons for
this difference, but I don't think we understand them yet.

As a consequence of this concern, there has been an incredible mobilization
of activity around the NEOTROPICAL MIGRANT question. Government money is
flowing freely, and there is an obvious clustering of agencies,
universities, and researchers around this source of money. Sadly, MIGRANT
seems to be the password to access this source of research funds. Because
of this, I think, both federal and local agencies and teams putting
together lists of "Neotropical migrants" feel the need to include as many
species as possible to get them studied and (perhaps) stabilized. Thus the
"bunch of hooey" to which Mike referred. Every list of "Neotropical
migrants" produced in the Northwest that I have looked at would have been a
laughing matter if I had not had the above insight. I have writen pages of
criticism about lists submitted to me that included species that, to my
knowledge, had been recorded even in *northern* (= anything but tropical)
Mexico on only a smattering of occasions! Many others migrate regularly
onto the northern Mexican highlands but couldn't (shouldn't) be considered
"Neotropical" in any context. Song Sparrow comes to mind as an example on
a recent list from Partners In Flight. Rock Wrens and Sage Thrashers are
listed on some lists, Pine Siskins on others. Species that have resident
populations on the Mexican Plateau apparently qualify, even when they are
nonmigratory. I could go on and on about these lists, but it is more
important to look at a larger picture.

The logical thing to do would be to look at all species, migrants and
residents, to try to find out what's happening with our avifauna. Only by
looking at residents do we have a "control" to assess population changes in
migrants. A recent fine analysis of Neotropical migrant populations in
Oregon and Washington by Brian Sharp is flawed primarily because
comparative info on residents was not analyzed (not his fault; his contract
didn't include residents). How can you blame the Latinos for population
declines if you don't know whether it is only "their" birds that are
declining?

Most "Neotropical migrants" from the Northwest winter in northern and
western Mexico, often in the uplands but also in the lowlands; some go
farther. Most "NMs" from the East winter in the West Indies, eastern Mexico
and Central America; some go farther. There really is a difference between
the two groups, as Mike implied, although plenty of Washington breeding
birds winter in the lowlands of the western Mexican states, tropical by
anyone's standards. Evidence of decline of western birds is still scanty,
but some species seem to be down in numbers. Nothing like the east--I was
horrified by how uncommon birds in general seemed in Maine last summer
compared with my impressions from Washington. Never having spent time in
summer in the Northeast before, I don't know if it was always like that, or
if there really is a dearth of birds, a la Rachel Carson's "Silent Spring."

If there's anyone out there who is actually participating in Neotropical
migrant studies, correct me if I'm wrong anywhere here. Thanks. Amazingly,
as I was typing this, a grad student (Phil Nott) from the U. of Tennessee
Knoxville came in, and we had a spirited discussion of American bird
population declines and their causes! He is working with Stuart Pimm, an
influential population ecologist and conservation biologist. Small
world....

Dennis Paulson
Slater Museum of Natural History
University of Puget Sound
Tacoma, WA 98416
206-756-3798
dpaulson at ups.edu