Drawing on past records compiled over several decades by bird-watching organizations in Ohio, two members of the Toledo Naturalists Association, Becky Cullen of Bowling Green and Eric Durbin of Holland, found that barn owl nestings were reported in 84 of the state's 88 counties in the 1930s but had vanished across Ohio by the 1960s.
Similarly dramatic declines in barn owl populations have been reported in many countries.
In British Columbia, which has Canada's main population of barn owls, official reports from Environment Canada estimated that the number of barn owls in the province had declined to as few as four to six pairs in 1987.
As agricultural land has shrunk rapidly to make way for housing and other development, many of the barn owl's preferred nesting sites have disappeared.
Where farms still exist, wooden barns have largely been replaced by modern, tightly sealed farm buildings of corrugated metal siding.
In the Florida Everglades, pump houses dotted along the networks of canals that weave through sugarcane fields were long popular as nesting sites. But these pump houses are disappearing now that canal irrigation is automated.
The barn owl's decline in many areas has caused much concern in recent years because of the bird's role in reducing rodent populations, which minimizes the need for expensive pesticides and is better for the environment.
According to a study of barn owls published by the Connecticut Department of Environmental Protection's Wildlife Division, a single family of two adults and six young can consume more than 1,000 rodents during a typical three-month nesting period.
Young barn owls have very high metabolism and at the age of five or six weeks can eat the equivalent of one-and-a-half to two times their weight each day. At seven weeks old, the fledglings may even weigh more than their parents, who expend energy hunting each night to feed their offspring.
Raid has calculated that in the agricultural areas of southern Florida's Everglades, sugarcane farmers lose $30 million a year from rat damage. In studies of the barn owl's diet, he found that as much as 90 percent of the predator's food consists of rodents, especially rats.
Many farmers use rodenticidesstrong chemical poisonsto kill rats and other crop-damaging rodents. Although barn owls regurgitate the skeletons of their prey in the form of "pellets," the birds sometimes die from the poison their prey has ingested.
A Turnaround Ahead?
Barn owls often use the same nesting sites year after year, and in many areas where nesting boxes have been installed to help revive barn owl populations, encouraging results have reported.
In Britain, the Hawk and Owl Trust credits the installation of nesting boxes with helping to reduce a steep decline in the country's barn owl population. According to the group, the number fell from about 12,000 pairs in the 1930s to 3,000 or so by the 1960s. Today, the group estimates that Britain's barn owl population is 4,000 pairs.
Many projects are underway in the United States and other countries to install nesting boxes to attract barn owls.
Under the Carolina Raptor Center's Project Barn Owl, nest boxes are being set up around Charlotte, North Carolina, to lure both barn owls and barred owls.
After Maryland's Natural Heritage Program placed the barn owl on its species "watch list," the state's Department of Natural Resources and the Southern Maryland Audubon Society launched a project to encourage citizens to install and monitor nesting boxes to attract barn owls and acquire research data.
Cornell University's Lab of Ornithology sponsors a similar project on the Internet, known as The Birdhouse Network, to aid studies of the population and reproductive success of owls and other declining bird species.
Research suggests that nest boxes placed atop poles in open fields are likely to be the most effective.
In one study, Raid and his colleagues found that owls had begun nesting within two months after nesting boxes were installed in farm fields. In contrast, it was three years before owls began roosting in nesting boxes placed in trees.
Paul Radley, a graduate student at Arkansas State University in Jonesboro, obtained similar results in a study of the nesting habits of barn owls in northeastern Arkansas. He found that the owls preferring nest boxes on farm buildings, away from trees.
"If there is a large population of non-breeding individuals in a given area, it's likely that habitat and food supply are not the issue," said Radley. "In this situation, an increase in suitable nest sites might be a good fix."
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