But for people along the East Coast who prefer to see birds that still have some flap in their wings, autumn is a time to keep the eyes peeled for the pocket-sized featherweight of the avian world: the hummingbird.
"I'm not that interested in hummingbirds during the summer," said Mary Gustafson, a biologist and chief ornithologist in the bird banding laboratory at the U.S. Geological Survey's Patuxent Wildlife Research Center in Laurel, Md. "Anybody who's got a hummingbird now can give me a call."
In recent years, Gustafson and other researchers have recorded an increasing number of hummingbird sightings along the East Coast in late fall and winter, when most birds already have flown south for the winter.
"Twenty or 25 years ago, if you said you saw a hummingbird in November, people would be wondering if you had been tipping the sherry," said Gustafson, who has banded three species during the winter in Delaware as part of an ongoing effort to better understand hummingbirds.
Gustafson said the East Coast winter sightings give researchers reason to rethink what they know about migration patterns of hummingbirds flying from western states and Canada to Central and South America.
Sheri Williamson, co-founder of the Southeastern Arizona Bird Observatory, said the sightings may be due to variations in the birds' internal compasses, coupled with increased public interest in hummingbirds.
"These birds are pretty plastic in their behavior," said Williamson, author of the new "Peterson Field Guide to Hummingbirds of North America."
The United States is home to 16 of the more than 320 known species of hummingbirds, which travel more than 4,000 miles in their roundtrip migratory treks. The rufous hummingbird from the Pacific Northwest accounts for a large number of the East Coast winter sightings.
Delaware has long been a hotbed of hummingbird activity.
H. Ross Hawkins, president and founder of The Hummingbird Society in Newark, credits former DuPont Co. president Crawford H. Greenewalt with sparking the modern world's appreciation for hummingbirds.
Greenewalt, a chemical engineer who helped invent nylon and later worked on the Manhattan Project, became an avid amateur ornithologist and photographer while president of DuPont. His use of new strobe-flash technology and development of a shutter-less motion-picture camera led to National Geographic articles and a 1960 book with color photographs of hummingbirds and new ideas about their flight dynamics.
Hawkins, a retired stockbroker, founded The Hummingbird Society in 1996, three years after Greenewalt's death. It now has about 2,500 members in all 50 states and in 26 foreign countries.
Public fascination with hummingbirds, which are found only in the Americas, isn't hard to understand. What other birds can hover, fly backward, sideways or even upside down while beating their wings at up to 3,000 times a minute and flashing rainbows of iridescent colors?
None, Hawkins noted.
The tiny birds - the smallest, the 2-inch-long Cuban Bee, weighs in at seven one-hundredths of an ounce - also are fearless.
"They are tiny, but they really are bad little dudes," said Bob Sargent of Clay, Ala., a retired electrician and master hummingbird bander.
Male hummingbirds have been known to attack hawks and small pets intruding on their territory, and even impale other hummingbirds with their bills.
"There's a saying that if hummingbirds were the size of hawks, we'd all run around in fear of our lives," Gustafson said.
Williamson and Sargent, who keeps about 60 feeders in his yard during the summer, are among fewer than 100 certified banders contributing data to Gustafson's lab, the federal repository for all bird banding data from the United States and Canada.
The banders tag the hummingbirds with tiny strips of laser-printed aluminum alloy that are so light 5,500 bands weigh just one ounce.
Williamson said information from the banding helps provide insights into the longevity, migration patterns and behavior of hummingbirds.
"It's an example of us getting to peak into the window of the lives of these birds," Sargent said.
By Randall Chase