The day after a rare snowstorm hit the state in early September with snow, cold, and gusts up to 70 mph, The University of New Mexico student Jenna McCullough received an email with a report of dead birds at the Tijeras ranger station. It was her first encounter with mysterious bird deaths that have saddened bird lovers across the state and nation.

McCullough studies avian evolution and systematics of birds in the South Pacific. She is a third-generation female birder and regularly travels across the western U.S. and internationally to follow her passion. She wrote an article about her recent findings for the American Birding Association (ABA), a report that has caught the attention of local and national media.

“The day after the storm, I was contacted via email by my supervisor, Mariel Campbell, the collections manager of the Genomic Resources Division of the Museum of Southwestern Biology, about birds dead and acting weird in Tijeras. We collected 10 birds there and in the Sandias,” she recalled.

In the ABA article, she wrote “We found several dead Empidonax flycatchers of three species, a Vesper Sparrow, and a Townsend’s Warbler. Some birds were wet from the overnight snow, but others were completely dry, huddled in the corners of buildings. A Dusky Flycatcher sat dazed in the parking lot.

“We first thought little of it. Mortality is expected for migratory birds, and we didn’t find more than a handful of carcasses. But social media told a grimmer story that night. We read reports of widespread mortalities across the state: dead swallows along a bike path in Albuquerque, a half-dozen Empidonax flycatchers and swallows in one park in Clovis, and a local news report of 300 carcasses recovered by researchers from New Mexico State University and nearby White Sands Missile Range. It was soon apparent that a significant mortality event had occurred.”

One report stood out to her. Local journalist Austin Fisher of the Rio Grande Sun newspaper posted a video on Twitter of dead swallows and told McCullough where she could find them. She and fellow UNM Biology Ph.D. student Nick Vinciguerra went to Velarde, NM, late that night to get the birds and, in all, found 305 birds.

“We wanted to document this die-off so the specimens could be used for future research and education,” she said.

Jenna McCullough
Jenna McCullough

The majority of birds were insectivores, meaning that they eat insects. Swallows, flycatchers, warblers are all insectivores.

“I would say swallows are the most affected. This is pretty common though, because swallows are very sensitive to these types of weather events because they are aerial insectivores. They only eat insects while flying around. If no insects are flying around, there’s nothing for them to eat,” McCullough explained.

“I am not ruling out the possibility that fires altered their migration, as there is anecdotal evidence of this. But I do not think the wildfire smoke killed them outright. Instead, the data points to starved birds  with very low body weight and poor muscle condition, lending credence to the hypothesis that it was lack of food plus hypothermia,” she noted.

In this case, they stopped in New Mexico, exhausted from migration with little fat, to find very few insects due to cold temperatures that either killed or made insects go dormant. Without fat, they have no protection from the cold and are very susceptible to hypothermia.”

Jenna McCullough, biology student and avid birder

“The birds that we collected were currently migrating through New Mexico. Migration is a very intensive time for birds. They will fly for hundreds of miles overnight. It depletes their fat stores, so they have little energy when they land at a critical stopover site. On a normal day, they will gorge themselves on food and build up their fat stores to continue. In this case, they stopped in New Mexico, exhausted from migration with little fat, to find very few insects due to cold temperatures that either killed or made insects go dormant. Without fat, they have no protection from the cold and are very susceptible to hypothermia.”

Basically, the birds died of starvation and cold.

The cold snap was natural and there was nothing anyone could have done, McCullough noted, adding that it’s a part of the natural risks for migrating birds.  The freak weather is over and reports she is receiving now about recent bird deaths are more likely just the normal number the UNM ornithologists get all the time. People are more aware of dead birds because of media coverage and are reporting them more now. 

The dead birds will be deposited into the Bird Division of Museum of Southwestern Biology on the UNM  central campus and research specimens and tissue samples will be cataloged in the Division of Genomic Resources.

Asked if there was a way to help migrating birds such as bird feeders or providing water, McCullough replied, “Well, the problem is over now. And this event is not the biggest threat to bird populations,” citing habitat destruction, fragmentation, pollution, and other factors.

One of the best ways people can help is simple.

“The biggest thing individuals can do is to keep their cats indoors, as pet cats have been shown to kill birds indiscriminately. It’s safer for the cat, safer for you, and safer for the birds.”

McCullough’s ABA article, The data behind mysterious bird deaths in New Mexico, can be read here.

Photo by Jenna McCullough: The 305 individuals laid out at the Museum of Southwestern Biology that Nick Vinciguerra and McCullough collected from Velarde, NM on 14 Sep 2020. All individuals will be deposited as specimens in the museum’s Bird Division for future research and education.