Researchers at the University of New Mexico think the alarming piles of dead birds documented all across the state earlier this month were primarily wrought by cold weather that killed off edible insects and induced hypothermia.
When New Mexicans began flooding social media with pictures of dead birds nearly two weeks ago, UNM Ornithology Ph.D. students Jenna McCullough and Nick Vinciguerra were collecting samples around the Sandia Mountains. That week, a cold front blowing down the Rocky Mountains south from Canada brought historic low temperatures and early first snowfalls to large parts of the state.
Since they were first reported, the deaths have caused a stir on social media and beyond, with many wondering whether the cold, fires, climate change or some other problem could have caused so many to die in such a short time. The state Game & Fish Department is still awaiting autopsy results from specimens sent to the National Wildlife Health Center.
On Sept. 13, a video of heaps of dead swallows in Velarde posted by former Española journalist Austin Fisher caught their eye, so the ornithologists hit the road to find hundreds of dead birds who had been huddled into the crevices of rocks, apparently searching in vain for warmth.
“I am no stranger to dead birds,” said McCullough, a third-generation bird-watcher, “but I had never seen anything like this. This was a lot of dead birds. It really is sad to see something like that.”
McCullough and Vinciguerra collected 305 carcasses, mostly violet-green swallows, and took them back to UNM’s Museum of Southwestern Biology. There, they documented a pattern of a lack of fat stores and atrophied breast muscles, signs of dehydration and starvation that McCullough and Vinciguerra hypothesize led the birds to succumb to hypothermia.
Beyond UNM’s samples, U.S. Forest Service Wildlife Program Leader Leslie Hay said the mass deaths have been seen in a wide range of bird species across the state. On the Southwest Avian Mortality Project, a website where the public can document dead birds, observers have marked 150 species of birds found dead across the Western United States and Mexico in recent weeks.
“Migration ties us all together. A bird might fly 5,000 miles from Canada to Costa Rica, so what’s happening in a forest here in New Mexico is important to our partners elsewhere,” Hay said. “We’re asking for help to collect as much data on these dead birds as possible because that data helps us generate theories about what’s happening.”
Hay added bird migration across New Mexico is heaviest in September or October, so another similar mortality event is still possible in the coming weeks as West Coast wildfires could be adjusting migration routes.
“It’s like if you’re used to driving to Denver and have your typical pit stops,” Hay said. “Migratory birds follow the same coastlines or mountain ridges and stop in the same forest. We’re very concerned the fires are interrupting their typical stopping points.”
At UNM’s Museum of Southwestern Biology, tissues from McCullough’s and Vinciguerra’s specimens will be extracted and frozen at nearly negative 300 degrees Fahrenheit. The museum has over 4 million specimens of plants and animals — including over 50,000 birds and the second-largest collection of mammals behind the Smithsonian Institution — that provide a database for research.
“We will have a complete molecular record of all the pathogens and parasites being carried by these swallows,” Museum of Southwestern Biology Director Chris Witt said. “The bright side of the tragedy is the carcasses present rich scientific opportunities.”
McCullough and Vinciguerra, who collected the samples while wearing head lamps around midnight and stayed up all night back at the lab documenting their findings, agree.
“This event will be a unique learning opportunity,” Vinciguerra said. “These birds will have a second life in the museum.”