Three years ago, when Debi Shearwater spied a hayfield peppered with hundreds of nesting Tricolored Blackbirds from her car, she immediately panicked. She was on one of her usual spring drives, wending her way through the sprawling ranches along California’s central coast, on the lookout for the birds’ dense colonies—and this one was in a particularly precarious position. The chicks weren’t quite old enough to leave their nests, and the surrounding farms had all harvested their crops. Shearwater felt sure this field would be next.
“I’ve seen a mowed colony,” she says. “I don’t ever want to see that again. All dead birds, everywhere. They all die.”
When she got home, Shearwater sent an email alerting everyone she knew in the birding community to the endangered colony. The message set into motion a chain of events, linking together state wardens, dairy farmers, a federal agency, and advocacy groups, to safeguard the birds.
The concern for a single colony wasn’t purely sentimental: Tricolored Blackbirds have declined from several million birds to a few hundred thousand today. Their large breeding colonies of thousands of birds now hinder the species, as each can represent a significant proportion of the population. Finding safety in numbers once kept the species safe—but that was before the birds met a predator like the plow.
These large colonies also present a challenge for people trying to help the blackbirds. To gain them legal protections (such as state or federal endangered species lists), conservationists have to prove the birds’ population is still in decline. And because Tricolored breeding colonies are loyal to no single location—they move around from year to year—surveyors are forced to keep track of a moving target. If they miss a few big colonies one year, their counts can be way off, making it difficult to demonstrate that the species needs support.
To get the most accurate counts, a group of partnering organizations, including Audubon California, the University of California, Davis, and the California Department of Fish and Wildlife, have organized a survey, held every three years in April since 1994, that looks far and wide across the state over a single spring weekend to identify all of the colonies they can find. These counts aren’t led by expert biologists but rather by trained volunteer birders like Shearwater. It’s these volunteers that make the counts, and legal protections, possible, says Samantha Arthur, conservation project director at Audubon California. “They’re the entire basis for understanding the population trends of this species,” she says.
Their hard work has paid off. This past April, the volunteer-led survey data spurred the California Fish and Game Commission to list the Tricolored Blackbird as a threatened species in California. And now the species is undergoing a formal status review under the federal Endangered Species Act. The decision is expected to come out in the coming weeks, says Arthur.
The birds don’t make it easy for surveyors. Tricolored Blackbirds are almost entirely bound to the state of California (except for a few birds that wander down to Mexico and the rare colony that breeds in Oregon or Washington). During most of the year, they hang out with starlings and near-identical Red-winged Blackbirds. It’s only during breeding season, from the end of March to early August, when onlookers can easily distinguish Tricoloreds as they assemble together in single-species colonies.
The largest gatherings today, hovering between 15,000 and 25,000 breeders, are a fraction of what they used to be. One survey in 1934 found a single colony spread over 60 acres, housing some 300,000 breeding birds—the same size as the human population of Pittsburgh, Pennsylvania. “There’s been nothing close to that,” says Ted Beedy, a veteran ornithologist who’s monitored Tricoloreds for more than 30 years.
The decline is especially worrisome because birds that gather in colonies have an unsettling tradition of going extinct. Passenger Pigeons, for instance, gathered in communal nesting sites of tens of millions of birds until the species was hunted out of existence a century ago. Beedy worries that pattern will repeat itself. “I have the same nagging feeling that the Tricoloreds could wink out the way the pigeons did,” he says—but wiped out by habitat loss, pesticides, and plows instead of guns, nets, and smoke.
When Beedy first started studying the birds, researchers couldn’t agree on how many were out there. The traditional survey method of revisiting the same breeding sites every year didn’t provide accurate counts. To rectify the issue, Beedy envisioned a massive reconnaissance-style effort to survey Tricolored Blackbird colonies throughout the state that would require the help of volunteers. This way, each survey would rediscover colonies anew.
In 1994, Beedy wrangled Audubon members, agency biologists, and other expert birders to census the birds over a single weekend in the beginning of spring. This was the beginning the state-wide survey that would be held for three days in April every three years.
When the survey weekend comes, it dominates Shearwater’s life. “This is a big ordeal. It takes a lot of time,” she says. She searches for colonies across her county, a two-hour drive from end to end. “I just live in my car that weekend,” she says.
Outside of the survey weekend, Shearwater and other volunteers continue to monitor Tricolored colonies. They have to be persistent. Sometimes, breeders will settle at a site, only to decide a few days later that they don’t like it, says Dan Airola, a wildlife biologist, who’s organized further efforts to monitor Tricolored Blackbirds in the foothills of the Sierra Nevada Mountains. In the breeding season, Airola wakes up at 6 a.m. on the weekends and hits the road to find and track colonies. Early in the spring, he’ll find thousands of birds constructing nests at a site. Then, when he returns the next week, the birds will have vanished, he says. “Every one.”
The same thing has happened to Shearwater. She’ll track a colony at one site for weeks only for the birds to disappear. Then she has to search for them all over again. “I felt like I was going on a merry-go-round,” she says. “I kept having to move as they moved.”
Through the years, hundreds of volunteers have helped in the survey effort. Last year, 89 birders visited over 800 locations for the state-wide survey.
The state process to list the species was backed by two types of crowd-sourced data: the state-wide survey records and eBird data provided by the Cornell Lab of Ornithology. Both datasets show that the species has declined significantly in the last decade. “This is a one-two punch,” says Nicole Michel, a quantitative ecologist with the National Audubon Society, who worked on an analysis of the state-wide survey. “We couldn’t do it without community scientists.”
Published in its final form last month, an integrated population model developed by the Cornell Lab of Ornithology using eBird data confirmed the population trends described in analyses by the California Department of Fish and Wildlife and the University of California, Davis. The model pointed to low reproduction as a possible cause of the decline over the past decade. “That no doubt had an important impact on California listing,” says Tim Meehan, a quantitative ecologist at the National Audubon Society.
After the state listing decision, scientists from the National Audubon Society recently completed a statistical analysis of the statewide survey data that showed a population decline of more than 30 percent over the last decade. These new findings and the results from Cornell's eBird data modeling will provide critical scientific evidence for the proposed federal listing. If the federal listing goes through, it will add a host of new protections. Officials would need to develop a recovery plan and designate critical habitat for the species. Right now, the current listing protects only individual birds from harm, not their habitat.
But the state listing has already proved its worth. When Shearwater found the breeding colony that she feared would be mowed down, she tapped into protections from the state designation (in place since 2015, when the petition for a state endangered species listing was first filed). Her email, sent on a Friday night, reached a biologist at the California Department of Fish and Wildlife, who contacted the farm’s landowner. The biologist ensured the field wouldn’t be plowed and arranged for the farmer to be compensated for his unharvested crop. By Monday morning the colony was no longer in danger, Shearwater says. “It was saved, just like that.”
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