Small bird, big energy: UNM research could help with land conservation causes

Research from the University of New Mexico biology department could help show how climate and land use change might affect hummingbirds that migrate through New Mexico.

Authored by Shayne Halter, Blair Wolf and Carlos Martinez del Rio, the Jan. 15 study looked at why hummingbirds use torpor — a hibernation-like state. Hummingbirds usually go into torpor at night when it is colder, and this can help them survive, Halter said.

“They live at a sort of metabolic knife edge where if they don’t get enough food, they don’t get enough energy day to day, they don’t survive,” Halter said. “They have certain mechanisms they can use to ensure they make it, especially when they migrate.”

Hummingbirds rely on different food sources to carry them through migration, according to Halter. With land use change and climate change, there may be more of what Halter calls “nectar deserts,” where the birds don’t have access to food.

“In this research, we’re defining what some of those limits are, and we’re getting a good idea of how much torpor can actually compensate for energy shortfalls in these birds,” Halter said.

Christopher Witt, a UNM biology professor and one of Halter’s Ph.D. committee members, explained that the research lends some urgency to conservation matters, especially in regard to recent wildfires affecting conservation areas.

“The question becomes much more urgent to understand how increasing temperatures are affecting fat levels in wild hummingbirds,” Witt said.

These future applications may also help with space travel, Witt said. Currently, the physical mechanisms of torpor are still unexplained, according to Halter.

“Imagine if we could understand: What are the mechanisms by which hummingbirds regulate their body mass?” Martinez del Rio said. “If we could understand that mechanism well so that we could apply it for animals.”

Witt said for the past 80 years, the two hypotheses surrounding torpor predicted that it was either used routinely or only in emergency situations. This study shows that the chances of a bird going into torpor can be predicted with precision based on the bird's percent of body fat and the model, he said.

“This is a really exciting thing,” Witt said. “This shows that the answer all along was kind of simple, we just needed the data on body fat to be able to see what’s happening.”

Martinez del Rio said that before collecting the data, he and Halter created a mathematical model to predict when a hummingbird might enter into torpor.

“He has discovered a rule that tells you whether a hummingbird will become torpid and save energy for the next morning — and not only that, but how long it will be in torpor,” Martinez del Rio said. “Imagine the precision with which these animals are regulating their facilities.”

Halter explained that the model looks at the cost-benefit analysis for a hummingbird going into torpor. Physiological risks include a compromised immune system and sleep deprivation, as hummingbirds are not asleep during this mini-hibernation.

“When a hummingbird is in torpor, it’s unaware of its surroundings and it’s vulnerable to predation,” Halter said.

Witt said the study was elegant and serendipitous. That the strengths of each team member led to an accurate model that may be able to help explain energy management systems in animals in the future, he said.

The team took precise measurements on hundreds of hummingbirds in the area of Mimbres, which is in southwestern New Mexico. Halter is currently working on three more papers with the data taken from this study. These papers will look at topics such as hummingbird demographics, using feathers as geomarkers, and the dynamics of torpor.

Marcela Johnson is a beat reporter for the Daily Lobo. She can be contacted at news@dailylobo.com or on X @dailylobo

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