Last winter's mish-mash of weather sent bird-watchers to their field guides as species showed up where they're usually not. Documenting irruptions of seldom-seen species throughout North America were thousands of participants in a volunteer-run and scientifically based program, the legions of Project FeederWatch.

Analysis of Project FeederWatch's 1995-96 reports at the Cornell Laboratory of Ornithology showed normally North-wintering birds to be feeding throughout the continent; apparent population shifts among house finches, which suffer a contagious eye disease; more rare-bird sightings; and an unsettling trend for the squeamish: more songbird-eating hawks at the feeders.

"It was an invasion year, continentwide, for typically irruptive species. Pine siskins, red-breasted nuthatches and common redpolls visited 25 percent or more of feeders in North America, and FeederWatchers saw a 36-percent increase in evening grosbeaks," said Ken Rosenberg, research coordinator of Project FeederWatch. "We think severe weather and availability of food had something to do with the irruptions."

Now beginning its 10th season, Project FeederWatch gathers scientific data from volunteer participants throughout the United States and Canada. The reports from volunteers, who pay a small fee to help cover project expenses, are analyzed at the Cornell Laboratory of Ornithology. These widespread scientific studies of winter bird populations, behavior and diversity would not be possible without the comprehensive network of FeederWatch observers in the field.

One such study tracks the spread of the so-called house finch conjunctivitis, the contagious eye disease caused by bacteria-like Mycoplasma gallisepticum . The 1995-96 FeederWatch reports showed a striking decrease in abundance of house finches in the Atlantic Coast states, where the disease is most prevalent.

"But blaming these declines on the eye disease is not that simple," said Andre Dhondt, the Morgens Professor of Ornithology who heads the Mycoplasma study at Cornell. "For one thing, house finch populations have remained stable or even increased in other states where the disease is now present. On the other hand, declines are occurring in California and the Southwest, where the disease is not known. Linking population changes with the spread of Mycoplasma will require careful analysis that takes into account recent weather patterns, changing finch distributions and migration behavior," Dhondt said.

Meanwhile, FeederWatchers continue to document the rapid increase of house finches in Midwestern states, where this species was virtually unknown in 1989, and increases continue in much of the Southeast. House finches are now the second-most abundant and widespread feeder bird continentwide, and they are gaining on the first -- the ubiquitous dark-eyed junco.

When the winter birds stopped munching seeds, the ornithologists started crunching numbers. Among their conclusions from the 1995-96 stack of more than 60,000 computer-readable FeederWatch data forms are these:

• Common redpolls invaded nearly all northern regions, from the Northern Rockies east to the Maritimes and New England, while smaller numbers reached the Mid-central, East-central and Atlantic Coast regions. Pine grosbeaks increased primarily in the Maritime and Great Lakes regions, while Bohemian waxwings stayed mostly in the Northern Pacific and Maritime regions.
• Red-breasted nutnatches and pine siskins were the most widespread irruptive species, invading every eastern and central region. The most nomadic and unpredictable of feeder visitors, the evening grosbeaks, staged a large irruption from New England and the Great Lakes south to the Gulf Coast regions. Observers in the Southeast and South Central regions saw a large influx of American goldfinches and purple finches, while those colorful visitors were difficult to find in New England and the Maritime regions last winter.
• An acorn crop failure in the Northeast was at least partly responsible for the unusual appearance along the entire Atlantic coast and Southeast of a non-migrating bird last winter, the white-breasted nuthatch. Other species known to be partly dependent on acorns for winter food, such as the tufted titmouse, blue jay and American crow, also showed an increase in the same regions.
• Both red-bellied woodpeckers and Carolina wrens expanded along the northern boundaries of their respective ranges, "possibly signalling a recovery from setbacks during the past few cold winters," Rosenberg commented.
• Sharp-shinned and Cooper's hawks appeared in a broad belt from New England and the mid-Atlantic states to the Central regions, FeederWatchers reported.

FeederWatchers also were asked to document the appearance of rare or unusual species, and 190 of them did, reporting birds that were rare, more abundant than usual or out of their normal range. A species that surprised many of FeederWatchers last year was the northern shrike, which turned up in greater-than-normal numbers in Connecticut, Ohio and Massachusetts. And at the other end of the continent and the thermometer last winter, several species of hummingbirds were reported in Louisiana and Florida. FeederWatchers in those areas were treated to the likes of calliope and broad-billed hummingbirds, which normally winter in Mexico.