|The Problem with Spotting Owls|
|"It may sound strange, but we have no count of exactly how many
spotted owls are out there," said Joseph Lint, a wildlife biologist
at the Bureau of Land Management. For the past twenty years Lint and
other scientists have been keeping track of owls by first-hand
observation. Lint explained that biologists pick out an area of land,
go into the forest, and search for pairs of male and female owls. When
the owls are spotted, researchers release mice and wait for the birds to
snatch up a free meal, said Lint. The birds usually take the food back
to their nests and the biologists follow. If any young are found in the
nest, the scientists band them. The banded, spotted owls are then
tracked down several years later to see how many of them survived and if
they are having young of their own.
During the course of one of these surveys, the researchers typically
track down a few hundred owls over a range of tens of thousands of
acres. Lint said the scientists use these numbers to infer the survival
rate of the owls, the total acreage of owl habitat in the area, and the
structure of that habitat. Theyve found over the past ten years
that the number of owls they've monitored have been decreasing at a rate
of about 4 percent every 5 years. "So there isnt a sharp decrease in the
survival rates of the owls tagged. The population is probably
stabilizing," said Lint.
Traditional methods of monitoring spotted owls are time and labor intensive. Individual birds must be caught and banded by hand. (Photograph courtesy U.S Fish and Wildlife Service)
|While this mark and recapture method is the only one proven to work,
it would be very difficult to use it exclusively to monitor the
25-million acres specified in the federal plan. The costs to maintain
personnel and equipment would likely run to $3 million a year, and it
would require a very large number of personnel (Lint et al., 1999).
Instead, a model was needed that could accurately predict the health of
the owl population in the Pacific Northwest using a minimum of
"One of the first steps [in developing a predictive model] is to know the extent of spotted-owl vegetation and the range of the spotted owl," said Jim Alegria, the manager of the Interagency Vegetation Mapping Project for the Bureau of Land Management in Washington and Oregon. He said the BLM and USFS agreed that the solution to their problem lies in Earth-imaging satellites. Over the next few years they hope to have old-forest growth and owl-habitat maps for Oregon and Washington.
The advantage of satellites is that they can map out an area of landscape in a fraction of the time it takes to chart the area on the ground. More importantly, advanced imaging satellites such as Landsat 5 and Landsat 7 render images that can be used to identify large expanses of vegetation on the Earth. The satellites' sensors can highlight where one type of vegetation begins and another ends (Townshend et al., 1993).
|Burgundy colored regions on this map represent the historical range of the northen spotted owl in the United States (it also extends north into British Columbia). One hundred-fifty years of logging, agriculture, and urbanization have reduced the amount of old growth forest (potential spotted owl habitat) by 85-90%.|