Birds on the ground

National Wildlife Health experts determined the huge bird die-off in mid-September was caused by the birds being emaciated.

    New results from a federal investigation into the cause of a massive die-off of migratory birds in early September reveal that nearly all the birds were emaciated in varying severities at the time of death.

    Hundreds of thousands, perhaps even a million migratory birds died suddenly across the state in the first week of September following an early winter storm. Biologists with the New Mexico Department of Game and Fish collected bodies from different areas around the state and sent them for examination to the U.S. Geological Survey’s National Wildlife Health Center in Madison, Wis.

    Kerry Mower, the Department’s wildlife disease specialist, 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 severely emaciated.”

    Those scientists found no evidence of contagious disease or poisoning from smoke or pesticides.

    “From the lab reports, Department biologists know that migrating birds entered New Mexico in poor body condition and some birds were already succumbing to starvation,” said a press release from the state Department of Fish and Game. “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.”

    Jenna McCullough, a scientist for the Museum of Southwestern Biology and Ph.D student at the University of New Mexico, formed a similar explanation based on measurements of corpses she made at the Museum. She shared her initial findings on the American Birding Association’s website and in an interview with the Rio Grande SUN in September, shortly following the die-off when she and her colleague collected hundreds of birds in Velarde.

    “I’m glad to see results from the necropsies much sooner than I expected,” she said. “The results, though from a representative sample of the samples sent to the USGS National Wildlife Health Center in Madison, Wisconsin, point to starvation and dehydration. These signs include shrunken pectoral muscles (which birds rely on for powered flight), empty stomachs, lack of fat tissue, and kidney failure.”

    She’s still waiting to complete an analysis of the birds she collected for the Museum that didn’t get sent off to the U.S. Geological Survey.

    “I haven’t done anything with the birds in the freezers of the museum yet—we are waiting on hearing whether a collaborator receives federal NSF funding for biochemical analyses on the bird carcasses,” she said.

    McCullough said although the cause was a freak weather incident, humans still need to be aware of their impacts on bird populations.

    “Though this points to a natural cause of the avian mortality event, I do not think that humans are off the hook when it comes to bird declines,” she said. “If I recall correctly, I spoke  “Habitat fragmentation and destruction, climate change, and feral cats have serious, negative impacts on wild bird populations. Regardless, I hope this necropsy report ends the non-mystery of what happened this fall to migrating birds in the Southwest.”

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