Starvation and climate-linked freak weather behind mass die-off of songbirds

Dead birds were found in states including New Mexico, Colorado, Texas, Arizona and Nebraska in September

New Mexico State University scientists documented mass die-offs of birds in the fall (Allison Salas/New Mexico State University)

Scientists have discovered why thousands of songbirds dropped dead earlier this year in the southwestern US.

Starvation and an unexpected cold snap linked to the climate crisis were the causes of mass die-offs, according to the US Geological Survey (USGS) National Wildlife Health Center in Santa Fe, New Mexico.

In early fall, people living in states including New Mexico, Colorado, Texas, Arizona and Nebraska began reporting discoveries of dead migratory birds.

Among the species documented by researchers at the New Mexico State University were warblers, woodpeckers, hummingbirds and loons.

Follow-up analysis by federal wildlife authorities found that nearly all the bird specimens showed signs of starvation. 

In a statement this month, Kerry Mower, from the New Mexico Department of Game and Fish, said: “The laboratory results are very informative but did not identify a single definitive cause of mortality. However, they did find that nearly all birds were severally emaciated.”

The scientists’ observations provided evidence that birds were flying on minimal food intake. Many birds were found to have severely shrunken breast muscles, which control their wings.

Kidney failure was also found in birds along with irritated lung tissues. Birds’ intestines also contained small amounts of blood, one of the effects of starvation.

Some birds had stomachs and intestines empty of foodstuffs, and depleted fat deposits where energy is stored for migration.

The birds’ starvation is likely linked to the severe drought which struck the southwest region this summer and continued into fall.

Biologists found that migrating birds had entered New Mexico in poor body condition and some birds were already succumbing to starvation.

The dire situation was compounded by a freak winter storm that hit the southwest over Labor Day weekend and lingered for several days.

The unexpected weather likely caused birds to become disoriented and fly into buildings and other objects. Some were struck by vehicles and many landed on the ground where cold temperatures, ice, snow and predators killed them.

Jon Hayes, executive director of Audubon Southwest, was unequivocal about the role that the climate crisis played in the birds’ mass die-off.

“Nothing in the new information changes my opinion that the ultimate driver of this is changing weather patterns in the West that are easily linked to climate change,” Mr Hayes said, noting that hotter weather, larger wildfires, and more intense storms placed additional stress on birds.

America has lost more than one in four birds in the last 50 years, according to the Audobon Society, amounting to nearly 3 billion birds. 

In September researchers including BirdCast.info,  a project run by Cornell University ornithologists, suggested that smoke from this year’s historic West Coast wildfires could be driving the mass die-offs. 

While the USGS National Wildlife Health Center in Madison, Wisconsin found no evidence of smoke poisoning in the dead birds, Mr Hayes and other experts indicated that wildfires could have pushed migratory birds off course and into the path of the freak storm.

“The birds could have been altering their migration path to avoid smoke plumes, thereby increasing the energy demand of their migration and causing exhaustion,” Mr Hayes added.

“The evidence they’ve shown regarding poor body condition could still fit that scenario, and so I think there’s still questions like the role of fire in particular.”