February 28, 2007
Study: Pygmy Owl Numbers Down
TUCSON, Ariz. -- A university study shows the population of a tiny endangered owl in northern Mexico has declined by an estimated 26 percent over the last seven years, a finding that environmentalists said bolsters their arguments for greater protection for the bird in Arizona.
Annual surveys by a scientist show the birds are continuing to decline in numbers, although there have been some years with rebounds, according to the University of Arizona study."There's been some variation in there," Aaron Flesch, a senior research specialist in the university's School of Natural Resources, said Tuesday. The tiny bird's numbers increased in 2005 and were similar in 2006 in northern Sonora, but "overall the trend is negative."
"Should this apparent decline continue, recovery strategies that rely on pygmy owls from northern Sonora and persistence of pygmy owls in the Sonoran Desert could be jeopardized," the report said.
The U.S. Fish and Wildlife Service put the owl on the endangered species list in 1997 because of population declines in Arizona. But the agency withdrew it from the list last year after determining it was not a distinct subspecies and thus not worthy of protection.
Developers hailed the decision, but environmental organizations fought it and eventually lost a federal court challenge.
The cactus ferruginous pygmy owl is only about 6 inches long and weighs less than 3 ounces.
Since 1997, surveys have found no more than 41 pygmy owls in the Arizona wild during a year. Last year, 28 were found in southern Arizona.
Flesch said the owls have been found recently in Arizona in the Organ Pipe Cactus National Monument, the Cabeza Prieta National Wildlife Refuge, on the Tohono O'odham Indian Nation, in the Altar Valley and near Tucson.
Flesch collected data from more than 100 nest sites in the Mexican state of Sonora within 75 kilometers of the Arizona border.
Flesch uses recorded tapes of the highly territorial owls to solicit owl responses. The birds have been found to respond 100 percent of the time.
The sounds are played at locations 400 to 600 meters apart along roughly 33 miles of washes, he said. Flesch also checks nest sites in the same cactuses year after year for occupancy.
Flesch reported detecting a total of 255 males at the sites in Mexico over seven years, including 55 in 2000 and 33 last year, which would represent a 40 percent decline. But he estimates the overall decline at about 26 percent.
Flesch said his count is based only on a sampling and a much more complicated computerized geographic systems analysis would be needed to reach that.
Last year, the only pygmy owl known left in Tucson was removed from the wild by the Arizona Game and Fish Department to establish a captive breeding population, Flesch said.
Reasons cited for the bird's continued decline include continued drought conditions and human land use, from agricultural development to cutting of wood.
Flesch said the number of eggs that the owls lay annually, or so-called clutch size, declines as winter rainfall dips, as does productivity and nest success.
"The status of the pygmy owl is clearly more precarious now than ever before," Jenny Neeley of Defenders of Wildlife said in a release. "Without appropriate protections, the very existence of the pygmy owl in the region is in grave doubt."