|
|
Home »
Birdwatching »
Birding Briefs »
Male birds outnumber females, hawk killings, nesting Kirtland's Warblers, flight calls, photos of pioneering Green-breasted Mangos, and other rare-bird sightings
Male birds outnumber females, hawk killings, nesting Kirtland's Warblers, flight calls, photos of pioneering Green-breasted Mangos, and other rare-bird sightingsBirding Briefs -- February 2008
Published: December 21, 2007 Male birds outnumber females, especially in threatened species, research finds
The vast majority of bird species produce about an equal number of male and female offspring. But a new review of published research on the sex ratios of adult birds has found that males outnumber females by 30-35 percent.
Paul Donald, a senior research biologist with the Royal Society for the Protection of Birds, compiled data on 173 species from more than 200 scientific papers and found that 105 species had more males, 64 were balanced, and 14 had more females. (Ten of the species had estimates in two categories.)
He published the findings in the October 2007 issue of Ibis, the journal of the British Ornithologists' Union.
The reason for the imbalance is that females do not live as long as males, says Donald. Predators are more likely to kill females while they're incubating eggs, and in migratory species, females tend to fly farther than males, "exposing them to greater risk as they leave the natal area and disperse across unfamiliar territory," he writes.
Populations of rare birds are even more male-skewed than most other species, often due to non-native predators. Eight of the 12 most male-dominated species Donald found are listed as vulnerable, endangered, or critically endangered by the World Conservation Union. They include the Oma'o of Hawaii, Bicknell's Thrush, and three parrots: Mauritius Parakeet, Kaka, and Kakapo.
"This means that many of the world's rarest species may be much closer to extinction than we previously thought," he says. "It is much easier to save a population with an excess of females than one with an excess of males."
Read about birdwatching in the White Mountains of New Hampshire, a place to see the Bicknell's Thrush. |
Thousands of hawks and falcons die as pigeon fanciers "shoot, shovel, and shut up"
An undercover investigation by the U.S. Fish and Wildlife Service has revealed that a pigeon breeder's club in California, Oregon, and other states has been killing thousands of hawks and falcons a year in violation of the Migratory Bird Treaty Act -- and bragging about it.
Members of the group, called the National Birmingham Roller Club, keep a specially bred pigeon that they believe deserves protection because it is easy prey for hawks and falcons. According to the club, the roller "distinguishes itself by its ability to 'roll,' or summersault backwards in rapid, tight rotations" in flight. The action makes the pigeon appear sick or weak.
Club members trap birds of prey in large box-like structures with walls of wire mesh. Then they shoot or torture them to death.
Seven men in California and five in Oregon have been charged with fatally beating and shooting Cooper's and Red-tailed Hawks and Peregrine Falcons. Similar charges were filed against men in Texas, Wisconsin, Washington, and New York. |
Investigators say the accused bragged about killing raptors at meetings and on Internet forums and instructed each other to "shoot, shovel, and shut up."
The incidents provoked "huge outrage" in Portland, Oregon, including calls for stiff penalties from the mayor and other elected officials, says Bob Sallinger, conservation director of the Audubon Society of Portland. His office offers a $1,500 reward for information leading to the arrest and conviction of anyone illegally killing birds of prey in the state.
Nine men have pleaded guilty. Their fines have ranged from $2,000 to $25,000, plus community service and probation. Two Oregon defendants were fined $4,000 each, an amount Sallinger called a "slap on the wrist." In response, Oregon Congressman Peter DeFazio proposed revising the Migratory Bird Treaty Act to make the intentional killing of a protected bird a felony rather than a Class B misdemeanor.
Read our blog for more about this story, including how FWS agents found and rescued the caged hawk pictured above. |
Warblers' flight calls aren't just for migration
Many species use the high-pitched, brief vocalizations that we know as flight calls to locate flock mates during nighttime migrations. But the calls might have other functions. New research suggests that they may be important in nesting, fledgling, and wintering seasons.
Andrew Farnsworth of the Cornell Lab of Ornithology observed the daytime vocalizations of 23 different wood-warbler species and found that half gave calls during the fledgling and wintering periods and that one, the Nashville Warbler, even gave them during the nesting season (though only occasionally). The warblers he studied gave the most daytime calls during the fledgling period. Nashville and Cape May Warblers called the most in winter.
The roles such non-migratory flight calls might play are uncertain. Farnsworth writes that birds may use them to keep family groups together, especially if they have recently hatched fledglings. The calls might also help reinforce non-aggressive behavior and indicate safety among the family group. During the winter season, the calls might communicate to species in a mixed flock that the vocalizer isn't a threat.
Farnsworth published his research in the September 2007 Wilson Journal of Ornithology. (For more on flight calls, see "Birds on the move," April 2004.) -- Jessica Eskelsen
Read "Since you asked" columnist Julie Craves's answer to the question: Why do geese honk? |
Kirtland's Warblers nest in Ontario
It was big news when Kirtland's Warblers nested in Wisconsin last summer -- so much so that it was the cover story of our October issue. In November, it was announced that the endangered birds also nested in Ontario, about 350 miles east of the primary breeding grounds in Michigan.
Biologists found a nest with two chicks on the grounds of the Petawawa military base in June, the same area where male warblers had been heard singing in 2006. The biologists kept the news under wraps until the parents and young birds had flown south for the winter.
Read about where and when to find Kirtland's Warblers in Michigan.
|
|
Not a registered member? It's free to sign up.
See great photos of birds, get birdwatching tips, learn about birding events, and more!
|