This story aired in the April 23, 2025 episode of Crosscurrents.
It’s Climate Week. And the Bay Area is full of animal lovers. So much so that some develop followings of human fans.
Over the past few years, Peregrine Falcons nesting on top of the campanile, the big clock tower, at UC Berkeley have become local celebrities. People have been able to watch them nest thanks to a webcam tracking their progress.
Now, for the first time since their arrival the birds have not been seen and scientists suspect that the culprit may be bird flu.
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Story:
Mary Malec has been studying falcons in the Bay Area for twenty years.
She makes regular visits to UC Berkeley to check in on two adult peregrines, named Annie and Archie, who nest here.
Mary is a volunteer with Cal Falcons, a dedicated team of scientists who monitor these birds. When Annie first arrived in 2017, the group set up a nest-box on top of the tower and Annie has nested here ever since.
"One of the best things about this site is it’s so well protected," Mary says. "The beauty of this is that we could put cameras up, we could communicate what's going on. We could educate, we can talk to the public, we can. We can get them engaged."
Last spring, hundreds gathered outside of the Berkeley Art Museum’s big screen to watch the video feed as four peregrine chicks hatched from their eggs.
The video feed of the falcon nest provides another enormous benefit. Mary, and her fellow volunteers are able to really study these birds. That is, until this spring, when they webcam went quiet. Mary reflects on their disappearance.
"You know, it’s clear now that they aren’t here."
The peregrine falcon is no stranger to an existential threat. In the 70s, they became an endangered species due to the impacts of the pesticide, DDT. It was used in agriculture to kill insects, and as it worked its way up the food chain into peregrines, it led to thinner eggshells which would break under the weight of the parent. By 1970, there were only two breeding pairs of peregrine falcons left in California and none east of the Mississippi.
After the US banned DDT, falcons rebounded. Since Mary has been monitoring them, she says that the population has only ever increased.
"No, in my time, the numbers have always gone up."
The numbers now tell a different story. The disease known as bird flu, officially called highly pathogenic avian influenza, or HPAI, has become a threat to the peregrine falcon. Mary thinks that’s what happened with Annie.
"If this is bird flu and it seems like it is, um, it's affecting. It's affecting Peregrines of all ages. It's affecting chicks, it's affecting juveniles, it's affecting young adults, and it's affecting older birds. It does weigh heavy on me, yeah."
Down in Santa Cruz, Dr. Zeka Glucs has been noticing the absence of peregrines as well. She explains what brings us to the coast today.
"We're going to take a look at a nest that has been occupied for about two, three years."
Zeka is the director of the Predatory Bird Research Group at UC Santa Cruz. She monitors around 50 peregrine nests all over Central California, and says that winter is peak virus season for these birds.
"Just like our flu season, right? Birds have flu seasons every year. Usually their low pathogenic avian influenza and not high pathogenic like this one is."
Highly pathogenic just means that the disease is more impactful on the species. In this case, for peregrines, it has meant fatal. In the past two years, two falcons - one at San Jose City Hall and another at Stanford’s Hoover Tower - were found dead and later tested positive for bird flu.
Zeka says that at her other nests, sightings are also down, "So that is, for me, what rings alarm bells that they're not quickly recovering from this."
When bird flu first arrived in California, scientists turned to data from other states. There are people all over the world studying these birds. They started a message board and began talking to each other about what they were seeing. Zeka outlines the benefits of such a network.
"Here I was kind of laboring away in our little corner of the world thinking, you know, this is important, you know, for our region that we have this record, right, that we can draw back on as needed. Just realizing that actually I'm a part of this huge network of folks doing the same thing and that when we put all of our data together, like that's where the power is."
Reaching a cliff, overlooking the ocean, Zeka spots two Canada geese. She says their presence is not a great sign.
"They don't usually sit on the same cliff that a peregrine falcon's nesting on. So we'll see, but I don't think we're going to see much here."
Looking down to the water level, Zeka describes the cave. "We're looking at a little pothole here in the kind of coastal cliff area, some sandstone, and this is where the birds nested for about three years before they disappeared."
This nest was once a sign of the population boom among peregrines. More birds meant more competition for the best nests, so some began making due in less ideal conditions.
She explains further, that there were at one time so many peregrines looking for nests, "that they were desperate enough to take that site."
Zeka conservatively estimates that were about 1,200 peregrines total across the state at the population’s peak. While she can’t say how many falcons have died this year from bird flu, her team has visited 44 nests this year. So far, nearly half are vacant.
The current strain of bird flu is impacting more than just peregrines. The virus spreads most rapidly in chickens and waterfowl, as Zeka explains, partly because those birds live in groups.
"That's why they're really great reservoirs for the virus is because they're able to move it around and they don't just die immediately."
Unfortunately raptors are not that way. Birds of prey, like falcons and eagles, are getting sick by eating infected birds. And because raptors tend to be more solitary, they aren’t building up a strong defense against bird flu.
Another bird that’s been hit really hard by the disease is the California Condor. Zeka describes the difference between their behavior, and that of the peregrine falcon.
"They have really complex social networks, if a couple of them get infected with a disease they can pass it through the flock pretty quickly. So they're just vulnerable to these kinds of things."
When bird flu hit the Southwest flock of California condors - 21 condors died. That number is especially worrying because there’s only about a hundred birds in that flock. Luckily, scientists were able to intervene.
"Birds were brought in from the wild and isolated," Zeka says. "And ultimately vaccinated. So hopefully that bullet has been dodged."
For the peregrine falcon, luckily the population was up when they first encountered this strain of HPAI. It may ultimately help the species survive bird flu. Zeka reflects on the benefit of generations of conservation efforts on behalf of the peregrine.
"I feel like I just feel a deep gratitude for the all of the folks that brought these birds back to the numbers that they had reached by the time that they were exposed to HPAI because they actually have a sturdy enough population to weather it. If this had happened when we only had you know a couple breeding pairs left then that could have been it, right?"
Among the reasons to be optimistic is that there is once again a falcon nesting at San Jose City Hall. On the city’s webcam she can be seen sitting in the nest box, keeping warm her recently laid clutch of eggs.
