Starvation, unexpected weather to blame in mass bird deaths

A lab report indicates starvation and unexpectedly cold weather were major factors in a mass die-off of migratory songbirds earlier this fall.

The U.S. Geological Survey National Wildlife Health Center analyzed representative samples of the migratory songbirds collected, cataloged and sent for analyses by New Mexico Department of Game and Fish biologists, in early September.

The lab report indicates a single abnormality shared by nearly all birds was body condition ranging from poor to severely emaciated.

“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,” Kerry Mower, the department’s wildlife disease specialist, said.

The single abnormality shared by nearly all birds was body condition ranging from poor to severely emaciated. These observations are evidence of physical exertion without nourishment to support recovery, including:

• The large breast muscles controlling birds’ wings were severely shrunken;

• Kidney failure was apparent in many of the birds;

• Stomachs and intestines were empty of foodstuffs;

• Many intestines contained small amounts of blood, one of the effects of starvation;

• Fat deposits, the stored energy for migration, were depleted;

• Lung tissues were irritated.

The USGS National Wildlife Health Center, located in Madison, Wisconsin, is renowned for the thoroughness of the diagnostic tests for wildlife disease diagnosis and management.

The center conducted tests during analyses, ruling out contagious bacterial disease, contagious viral disease including avian influenza and Newcastle disease and parasites as cause of death, as well as finding no evidence of smoke poisoning or pesticide poisoning.

From the lab reports, department biologists know migrating birds entered New Mexico in poor body condition, and some birds already were succumbing to starvation.

The unusual winter storm exacerbated conditions, likely causing birds to become disoriented and fly into objects and buildings. Some were struck by vehicles, and many landed on the ground where cold temperatures, ice, snow and predators killed them.

“The department would like to thank many partners and the public who reported mortalities across New Mexico,” said Erin Duvuvuei, the Department’s avian biologist. “Hundreds of reports were received through email, phone calls and the iNaturalist app.”

Reports of bird deaths declined by late September.