Wild Cam: Drought brings drinking problems for Tequila bats

Not everybody can say they love their job. But TWS member Mallory Davies was right at home rappelling 30 meters down a hips-wide chute to a cave floor nearly boot-deep in bat guano. Her mission? To gather fecal samples in one of the only known roosts of both Mexican long-nosed and lesser long-nosed bats located near Hachita, New Mexico.

“This [cave] is really special and unique,” said Davies, a bat researcher at the University of Arizona and an organizer of TWS’ Out in the Field community.

Davies’ efforts were going to help her track both bat populations. She had previously noticed something amiss in the behavior of the lesser long-nosed bats (Leptonycteris yerbabuenae) and Mexican or greater long-nosed bats (L. nivalis). Instead of feeding only on nectar from agave plants, they seemed to be consuming a fair portion of insects and sugar water—behavior that goes against conventional wisdom for the species. Davies and her colleagues wanted to know why. They thought the change in diet could be related to a combination of changing climate patterns and urban development.

Tequila problems

Lesser long-nosed bats (pictured above) and Mexican long-nosed bats typically migrate between the southwestern U.S. in the summer and Mexico in the winter. They also live year-round in parts of southern Mexico and Central America.

The U.S. Fish and Wildlife Service listed both the Mexican long-nosed bat and the lesser long-nosed bat under the U.S. Endangered Species Act in 1988. The agency delisted the latter in 2018, according to the Federal Register. The Mexican long-nosed bat remains federally endangered.

But conservation challenges persist, even for the lesser long-nosed bat. The species, also known as the tequila bat, is a pollinator that mainly feeds on the nectar of the agave plants also used to produce tequila and mezcal in Mexico. But the bats in the southern part of their range are running into some trouble.

While some mezcal producers use a more sustainable agave plant selection, tequila producers—and some bigger-market mezcal producers—are replacing wild agave plants with cloned monoculture crops to create more product. Since producers of both liquors—tequila is really just a type of mezcal—harvest agave plants before they flower, lesser long-nosed bats are finding it increasingly hard to find nectar in parts of Mexico, such as the region surrounding the town of Tequila.

“They are converting this landscape and not letting any of it go into flowering,” Davies said.

Meanwhile, in the northern end of the bat’s range in the southwestern U.S., climate may be causing a mismatch between the flowering times of agave plants and the migration time of the species. For one reason or another, nearly the whole nectar corridor from Mexico to the southwestern U.S. faces threats.

What the bats are eating

Davies, who presented her ongoing work at the 2024 TWS Annual Conference in Baltimore, Maryland, studies populations of both species that roost in the U.S. Bureau of Land Management’s Big Hatchet Mountains Wilderness Study Area in New Mexico (pictured above)—the largest known roost site for lesser long-nosed bats in the U.S. with thousands of individuals—as part of her PhD dissertation work. This area is a post-maternity roost for lesser long-nosed bats—a place where mothers bring their young after they learn to fly. There, the young bats feed on nectar before making a 1,600-kilometer journey down to Juxtlahuaca in the state of Guerrero in southern Mexico for the winter.

Davies wondered why the bats stopped in this area at all—the timing just didn’t make sense. “They are coming before the agave is available and staying months after the agave is done blooming,” Davies said.

To learn more, she and her colleagues began gathering fecal samples from the bats in 2020, targeting both long-nosed bat species and another nectar bat—the Mexican long-tongued bat (Choeronycteris Mexicana). They laid plastic tarps on the ground before the bats arrived to roost in January. Then, they collected the samples from the tarps the following January and set out new ones.

DNA analysis of the years’ worth of guano samples revealed which species roosted there, since it’s nearly impossible to tell the difference between Mexican long-nosed and tequila bats by just looking at them. In fact, they found evidence for 11 species inside or near the cave, including Townsend’s big-eared bats (Corynorhinus townsendii). It also revealed that the bats in this area have a more varied diet in the Big Hatchet Mountains than previous research had found.

“During periods of drought, we’re finding fully aquatic insects in their diets,” Davies said. While researchers noted the bats sometimes indulged in the occasional ground insect, the sheer proportion of aquatic insects is odd, Davies said—and she isn’t even sure it’s intentional. They might be ingesting aquatic insects incidentally at a higher rate than usual while drinking water during drought periods. Or they may be targeting water with a little extra protein in it on purpose when times are hard. Davies hopes to answer this question in her ongoing research.

Something else is going on when it comes to tequila bats’ diets, though. As part of their research, Davies and her colleagues also examined evidence from trail cameras left on backyard hummingbird feeders within 100 kilometers of the roost site in Rodeo and Silver City in New Mexico and in Portal, Arizona. Footage there revealed that when only a few flowering agave plants remained, the numbers of bats taking advantage of the artificial nectar left at these feeders spiked. In fact, nectar bats such as the Mexican long-tongued bat pictured above are sometimes foregoing their usual migration south to Mexico, staying in urban areas and feeding on sugar water and insects in the U.S.

It’s possible that the bats are adopting a quirkier diet, whether it’s insects or artificial nectar, in dry periods due to a shortage of agave in the Big Hatchet Mountains. Davies, pictured above with a lesser long-nosed bat, said that young agaves can’t survive drought. The young plants are also more susceptible to javelinas (Dicotyles tajacu) eating them in dry periods. It takes years for agaves to reach their flowering stage, after which they wither and die. As extended drought periods are becoming more common in the northern Chihuahua Desert, both Mexican and lesser long-nosed bats may be seeking new food sources as the region loses flowering agave plants.

The ability of bats to change their diet in response to changing food availability is good news in some ways. “These bats are very plastic in their diets,” Davies said. “I think they are taking advantage of anthropogenic resources like water troughs and hummingbird feeders.”

Making improvements

In the southern portion of the bats’ range, conservationists led by the National Autonomous University of Mexico are making efforts to improve the availability of flowering agave in mezcal regions in Mexico. They are giving producers a bat-friendly certification when they improve the sustainability of their production. That may be through measures like allowing 5% of their agave to reach the flowering stage. 

In the north, Davies worries about whether bats drinking sugar water will sustain the population long-term or whether it will be as nutritious for long-nosed bats. While she hasn’t conducted population-level studies on the health of the bats, many of those the team does study have low body weight and appear unhealthy. “It doesn’t seem ideal,” Davies said.

She also wonders whether hummingbird feeders may act as a disease reservoir for long-nosed bats. There is still a lot that biologists don’t understand about these species, but she hopes to learn more about why the bats choose to stay in the area past peak blooming seasons in her ongoing work.

This photo essay is part of an occasional series from The Wildlife Society featuring photos and video images of wildlife taken with camera traps and other equipment. Check out other entries in the series here. If you’re working on an interesting camera trap research project or one that has a series of good photos you’d like to share, email Josh at jlearn@wildlife.org.