Who goes there? Rare Yosemite owls studied via sound
The birds are sensitive to human disturbance, so microphones are filling the knowledge gap.
Tue, Oct 23, 2012 at 12:45 PM
The magnificent birds known as great gray owls live throughout much of Canada, Alaska and the northwestern United States, but the tiny population that lives in California's Sierra Nevada mountains are just a little bit different than the rest of the species. These rare Yellowstone great gray owls were separated from their brethren during the last ice age about 30,000 years ago and subsequently evolved into a separate subspecies, Strix nebulosa Yosemitensis.
Today just 200 or so of the California owls exist, and scientists are trying to study them without causing them irreparable harm. It's not easy because the birds are extremely sensitive to human interference. "They will abandon their nests if disturbed," Steve Thompson, branch chief of wildlife management for Yosemite National Park, told the Associated Press. "It's an extremely low population, very vulnerable to natural- and human-caused events. They don't have the ability to rebound the way more abundant species do. We're very protective of them."
The birds are protected as an endangered species under California law, although they are not currently on the federal endangered species list.
Protecting the Yellowstone great gray owls requires that scientists gain a greater understanding of how they live and what habitat they require, but capturing the birds to study them, as is common with other species, is out of the question. "It's traumatic for them in the long term," UC Davis PhD candidate Joe Medley told the AP.
To solve this problem, Medley has moved away from physical examinations, such as blood samples, to using another tool: his ears. He placed a series of digital recorders near some well-known owl habitats, collected a huge amount of data, and then wrote a computer algorithm to sort through the information. Medley told the AP that his program — a customized version of the Raven Pro software from the Cornell University Laboratory of Ornithology — can identify which owl calls on the recordings were made by males, females or juveniles. The program is still working its way through 50 terabytes of data, something it would have taken a human researcher seven years to accomplish.
According to the Yosemite Conservancy, which is just one of the agencies partnering to complete this research, the recordings will be used to "locate owl nests and identify potential disturbances in the surrounding vicinity." Once nest locations have been identified, the conservation agencies will take steps to make sure that humans don't encroach upon them. The owls are popular with bird watchers, who can unwittingly disturb them and cause reproductive stress.
Yellowstone great gray owls were only confirmed as a separate subspecies in 2010. According to the National Parks Service, the California population is genetically distinct from the main species and displays different migration patterns, prey preferences and nest-site selection habits.
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