"These behaviors might not be innate," Beissinger said.
When extreme temperatures threaten adults, they can become dehydrated or stressed.
"They may leave their nest to eat or drink and may expose the young," Wolf said. "When it's really hot, the adults often suspend activity. They may not be motivated to feed the young."
Young Cooper's hawks like Patient #2021-2732 often move around in nests, even before they're able to fly.
"They may well jump out in the heat if they get too much stress," Wolf said.
Birds' overall heat tolerance varies not only by species, but by region.
In experiments, Wolf has tested and measured birds' physiological responses in a device called a metabolic chamber.
Wild birds spend about three hours at rest in these darkened chambers, as Wolf manipulates environmental conditions, like air temperature, and measures their responses. The birds are pushed to their limit, then released unharmed, helping Wolf examines species' endurance limits in a warming climate.
The research suggests the same species of bird would fare better in heat if it lived in Silver City, New Mexico, rather than Seattle. Their bodies are better acclimated.
"The largest natural killer of humans is heat," Wolf said. "Birds are more adapted to deal with heat, but not temperatures like this when they don't see them normally."
Die-offs of birds during terrestrial heat waves are "highly unusual," Wolf said.
Researchers have documented a few, including a pattern of deaths in South African swallows when high temperatures climbed above 109 degrees.
Climate scientists expect heat waves to increase in intensity and frequency.
With climate change, Wolf said damaging heat waves — such as those once expected every 50 to 100 years — could increase in frequency until they become almost routine. Wolf expects "that continuous stress on animal populations" to hamper many species of birds.
But the impacts of climate change are uneven, Beissinger said, and the Pacific Northwest's varying topographies and climates make it challenging to predict exactly how birds will adjust, Beissinger said.
Some species could move, seeking a new "thermal niche." Others are changing migration patterns or when they nest.
But Wolf fears warming will outpace birds' ability to adapt and evolve, particularly as direct threats like heat waves combine with other problems, like habitat and resource shifts.
"It's happening so rapidly," Wolf said. "This is another stressor stacked on top on an already declining community."
When Brown returned to the ground in the Matthews Beach neighborhood, his T-shirt was dotted in downy feathers, not an unusual site these days.
Work had become a "marathon" for Brown as PAWS scrambled to reunite heat-affected birds with their families or with fosters. The goal is return the birds to their families as soon as they are healthy and can fly.
He was hopeful for Patient #2021-2732, who hadn't accepted his chosen branch, but remained close enough to the nest from which she'd apparently jumped three weeks ago. She'd made a racket — a good sign.
"They're aware of her now," Brown said of her siblings and parents.
Minutes later, Brown heard a cacophony of cries from the siblings. An adult hawk approached, presumably with prey.
"That's Dad," said Deal, who had scouted the release site and found the nest. "This is what we wanted to hear — commotion."
With a little luck — and a lot of human help — Patient #2021-2731 would follow those cries back to her family and survive the heat wave that rattled her nest, her ecosystem and much of the Pacific Northwest.(c)2021 The Seattle Times Distributed by Tribune Content Agency, LLC.