The major threats to their continued survival are the mosquito-borne West Nile Virus — and humans. A female believed to be the cohort's most reliable breeder was struck and killed by a car in the park in August, prompting slower speed limit warnings to protect the low-flying raptors that rarely lift more than 20 feet above ground.
Because of their rarity, they are highly sought out by birdwatchers whose presence in meadows can deter mating and food foraging, the researchers say. That's why no one will reveal exactly where in the park they are.
"They will abandon their nests if disturbed," said Steve Thompson, Yosemite's branch chief of wildlife management. "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."
So protective that the owls will no longer be trapped to draw blood for studies. Instead researchers are collecting molted feathers to extract and amplify DNA to track lineage, mating patterns, population size, survival rates and even genetic mutations that might occur as the climate changes yet again.
"Genetic mutations occur randomly. It's just chance whether those mutations are advantageous or deleterious to the population," Thompson said. "And all of this is happening over tens of thousands of years, so to me as a biologist it's really exciting to have this demonstration of how evolution occurs."
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