At least 5,000 birds have died so far this summer in a network of wildlife refuges along the Oregon-California border, fueling fears of another major disease outbreak and calls for more water releases in a region plagued by drought and water shortages exacerbated by climate change.

The deaths were likely caused by a rare combination of bird flu and botulism, said John Vradenburg, senior biologist at the sanctuary. In July, bird flu caused by the virus was confirmed in one of the sanctuaries, Vradenburg said. Bird flu has been on the rise in recent years and has led to the deaths of poultry and wild birds.

Botulism, which paralyzes birds from below until they can no longer fly and then can no longer breathe, is caused by a toxin produced by bacteria living in the soil. Tests for botulism in the sanctuary are pending, but the symptoms closely resemble previous botulism outbreaks, Vradenburg said.

The six refuges, collectively known as the Klamath Basin National Wildlife Refuge Complex, form the largest wetland network west of the Mississippi River. They are a stopover for 80% of birds migrating along the Pacific Flyway, a major north-south flyway for a variety of migratory birds in the Americas that use the refuges to rest, water and feed.

In 2020, at least 60,000 waterfowl and waders died of botulism in the protected areas. It was the worst outbreak in over four decades.

Botulism is common in wetlands, but conservation experts say the problem has become even more acute in the age of climate change, as extreme heat dries out large swathes of wetlands and warms the remaining water and mud, allowing bacteria to proliferate in shallow, stagnant pools.

In the Klamath Basin, the situation is made worse by the struggle for water. The water supply – which comes mainly from Upper Klamath Lake and the Klamath River – is divided between farmers who must irrigate 150,000 acres of crops and ranches, native tribes and endangered fish species. Even in years of plenty, there is not enough water.

In recent years, when drought hit the basin, the protected areas received little or no water. This year, although they received some water, they dried out due to the summer heat.

Bird flu, which has wiped out wild and domestic birds around the world in recent years, including in Oregon, is making the situation in the reserve even more difficult this year, Vradenburg said.

In mid-July, shelter staff began collecting dead great crested grebes, all of which tested positive for a more deadly strain of bird flu. Other species of birds that also died tested positive for a less deadly strain of bird flu that causes few or no symptoms of illness, leading staff to suspect that another disease – botulism – was the culprit, he said.

Typically, staff are able to rescue and rehabilitate some birds infected with botulism. In 2020, more than 2,000 birds were rehabilitated and released into the Klamath Sanctuary. But avian flu is making it difficult for sanctuary staff to respond to bird deaths. Although the disease does not pose a high risk to humans, some people have contracted avian flu viruses, requiring sanctuary staff to wear protective suits and limit their handling of the birds.

Refuge staff and bird conservationists hope there won’t be a repeat of the 2020 outbreak, Vradenburg said. That’s especially true because the wetlands are teeming with birds – ducks, geese, grebes and waders – this year, after two wet winters and a healthy release of water earlier this year from the Klamath Project, a state-managed system of dams, canals and pumps.

“The protected area is currently very productive, which makes it much more valuable for a greater diversity of bird species,” Vradenburg said. “It’s super rich in food and has really good habitat quality, so a lot of birds are sitting in the wetlands.”

Earlier this month, wildlife activists called on the Klamath Project to send more water to the refuge complex. On Saturday, the U.S. Bureau of Reclamation delivered additional water to two of the refuges, Tule Lake and Lower Klamath, where most of the birds die.

Teresa Wicks, a biologist with the Bird Alliance of Oregon who visited the sanctuary earlier this month, saw dozens of dead and paralyzed birds and helped to break the alarm. Wicks said the water release is not as large as advocates had hoped, but should give the birds – particularly young waterfowl and aquatic birds that hatched at the sanctuary this year – a chance to survive.

“It’s certainly better than no water at all and probably increases the likelihood that the birds will reach adulthood and move on,” Wicks said.

Releasing the water should also reduce disease pressure from bird flu and botulism, Vradenburg said, because more water in the wetlands means birds can spread out and drink cleaner water.

Lower temperatures also help break the disease cycle. Sanctuary staff are still seeing dead birds, but not as many, he said. Last week they collected 350, compared to 500 the week before.

In the long term, Wicks hopes local farmers, tribes and wildlife activists will find a solution to allow more water to be directed into the wetland each year. Although the demolition of the basin’s dam, which is scheduled to be completed this year, will not affect water allocations to farmers or the conservation complex, the demolition has sparked a discussion about the wetland’s role in maintaining clean, cool water for fish.

“The wetlands in the Klamath Basin used to function like a sponge. They soaked up the water that flowed into the river. And in the summer they let the water flow back into the river, where birds and fish lived together,” Wicks said. “Today it often seems like a system at odds. But with the construction of the dams, people have had more opportunities to think creatively about how to restore the natural hydrology and synergy.”

— Gosia Wozniacka reports on environmental justice, climate change, the energy transition and other environmental issues. You can reach her at [email protected] or 971-421-3154.