HERMISTON — Sixteen years after the burrowing owl population in Umatilla County bottomed out at only four nesting pairs, the population has hit a new high.

The 2024 nesting season has seen 100 nesting pairs, compared to the previous high of 65 pairs and an average of 54 pairs over the last 10 years.

These changes are the result of interventions, observation and research David H. Johnson and his team conducted during the past decade and a half at the Raymond F. Rees Training Center at the former Umatilla Chemical Depot a few miles west of Hermiston.

“This is a rescue mission,” Johnson said of the repopulation attempt, “and it’s working.”

Burrowing owls, when fully grown, weigh about 6 ounces, with the females being slightly larger than the males, especially before laying eggs and incubating them. They’re about 6½ inches tall with a wingspan of about 23 inches.

Johnson, director of the Global Owl Project, said to imagine the small birds like “an orange with wings.”

The owl population dwindled due to a cascading issue. In 1969, 14 pronghorn antelopes were introduced to the depot grounds. With time, their population grew and then began to crash.

Managers believed coyotes were hunting young pronghorns, so they started a coyote-control program, which accidentally resulted in trapping badgers, leading to a lack of the badger tunnels in which the owls nested. The cause of the pronghorn population decline has since been attributed to inbreeding, causing low genetic diversity, but by then the damage to the badger and owl populations was done.

When Johnson was called in to help the burrowing owl population in 2008, he didn’t have much information to go on.

Don Gillis, who was at the time the natural resource manager at the depot but has since died, told Johnson the population was in danger and needed saving.

“The study, starting in 2008, really allowed us to gain tremendous insights into burrowing owl ecology, migration, reproduction and management,” Johnson said.

Rebuilding habitat

Johnson started with designing an artificial burrow for the owls, as he suspected the lack of badger tunnels contributed to the low population numbers.

Each artificial nest has a slightly curved, nonperforated, corrugated 6-inch plastic drain line buried underground that leads to a halved 55-gallon barrel in the ground and covered by a removable 3.5-gallon pail. Making the pail removable allows researchers to see into the barrel to check the number of young in each nest as well as band them for tracking purposes.

Johnson placed the artificial burrows near the natural ones, which only last for about a year and a half before collapsing, so they would have a higher chance of use. Johnson’s team installed the first artificial nests in July 2008 and banded 40 owls in 2009.

The owls are an important part of the local ecosystem, Johnson said.

“They eat a lot of small mammals and insects, they’re beneficial,” he said. “The owls are doing the National Guard a lot of good.”

By catching mice, some of which carry viruses that can transfer to humans, the owls are helping to keep soldiers healthy.

Burrowing owls are crepuscular and nocturnal, meaning they are most active during the time between just before sunset and just after sunrise. The males are the primary protectors and hunters, with the females looking after the young.

Selecting a mate

Mate selection is one of the knowledge areas Johnson’s research has improved on.

In general, females choose who to mate with. They select a male of similar size and age to themselves. In low-food years, Johnson said, the smaller pairs are more successful because they require less sustenance.

“Where it’s really valuable is as people go about trying to do recovery work in places where they’re really endangered, this is a really important aspect of mate selection,” he said. “Knowing this has a really important bearing on long-term management and recovery work.”

Additionally, the nest location the males choose can impact their success in mating and keeping offspring alive. The more successful nests tend to be in wide open areas, away from any tall perches where birds of prey or other predators can keep watch.

While most of the population goes south for the winter, Johnson said, many of the older males from the Umatilla site actually migrate to east-central Washington.

“If they survive the winter, they’re first back and get first dibs on the breeding sites,” he said. “It was really unexpected. The young males will go to California, but the problem is if you go to California, you’re never first back, so then you get marginal territories.”

Protecting their young

Once their female lays eggs, male owls will decorate the area around their burrow entrance with animal scat, corn cobs, potato skins and other small tokens. The decorations mark a male’s territory, and the older they get, the more they decorate.

“It’s a male-to-male communication system,” Johnson said. “The males tell other males, ‘This site is occupied by a tough guy.’”

Decorating for dominance means the males don’t spend as much energy protecting their nests or females against other males and they have more security. The approach minimizes their stress and intraspecific competition.

In the clutches

Female burrowing owls in Eastern Oregon lay their eggs sometime in late April or during May. They will lay an average of eight eggs in a clutch, Johnson said, and the incubation period is about 23 days. Females start incubating with the fourth or fifth egg laid.

“The last two years have been really reproductive,” Johnson said. “And now we have El Nino in a mild winter and not a wet spring here.”

With a drier, warmer spring, the vegetation is more contained and the owls can better see their prey. But if there’s cooler weather in the spring, it can lead to higher death rates among the hatchlings.

“Three days of cold, wet weather will cut the reproduction in half, because the males can’t hunt very well, and three days is all the youngsters can go without food,” he said. “They get cold, they get hypothermia, they die.”

The past two years have seen 670 hatchlings, Johnson said. It’s rare for eggs not to hatch, but in years with worse conditions, some of the young will die due to lack of food.

‘A turning point’

So far this year, of the record 100 nests, the research team has captured and banded 98 females and 98 males as well as 402 young from 82 nests. Banding the owls allows researchers to track the owls’ success throughout the year.

Three of the nests are natural and likely made by a female badger.

The data and lessons Johnson has collected from this study will make efforts in other regions or countries easier, he said.

“The burrowing owls are declining and the things that we have learned on the depot will contribute substantially to the recovery and conservation of owls across their range in the Americas,” he said.

Although there would likely be benefits to continuing the study beyond this year, Johnson has decided to finish it and begin analyzing, writing and publishing the data he’s collected.

Johnson has stage four colon cancer, and he said he wants to publish this work and make it free and publicly available while he’s still alive. He hopes that others will perform longitudinal studies on how burrowing owl populations recover and how they fluctuate year to year.

The story of the Umatilla County burrowing owls is “an incredible success story,” Johnson said. The population has rebounded in a huge way in just a few generations, without relocating owls from other populations or doing any captive breeding. And the badgers are beginning to return, as well.

“We all need to work together for conservation,” he said. “I still hold onto the perspective that we want to keep common species common and keep them off of the endangered species list.”

The interventions work, he said. It takes generations, but it can be successful.

“I’m excited,” he said of preparing to publish his research. “… I think this will be a fundamental turning point in burrowing owl conservation. I know it will be. It already is.”

Burrowing owls have about 14 vocalizations, though some are specific to males or females. When threatened inside their burrow tunnels, the adult owls will make a sound resembling the hiss of a rattlesnake.

David H. Johnson, director of the Global Owl Project, said the trait makes evolutionary sense because the geographic distribution of burrowing owls and rattlesnakes overlap.