TUCSON (CN) – Standing in her back yard one morning, Bea Manderscheid noticed her hummingbird feeders were empty, an unusual sight because the tiny birds that sip the sweet nectar each day never finish it.
With a bit of sleuthing, she discovered the creatures that swooped in at night and slurped the sugarwater were tiny furry bats.
“One evening I saw a feeder swing and then I saw a flash – they’re so fast,” Manderscheid said.
She and her husband Gerry learned that the nocturnal guests that first visited their Tucson home eight years ago are lesser long-nosed bats, an endangered species in the United States.
The couple has fed the bats every year since, monitored and recorded their behavior to help conservation efforts in the Tucson area. The U.S. Fish and Wildlife Service credits citizen scientists like the Manderscheids for helping to improve the health of the species.
In early January, Fish and Wildlife Service announced that the migratory bat is stable and proposed to remove it from the endangered species list. When the lesser long-nosed bat landed on the list in 1988, there were believed to be fewer than 1,000 of them at about a dozen roosts, said Scott Richardson, a supervisory biologist with Fish and Wildlife.
The agency estimates that the population has recovered significantly, to about 200,000 bats at 75 roosts.
When the species flirted with extinction nearly three decades ago, human disturbance to the plants they feed on – agave, saguaro and organ pipe cactus – was largely blamed for the nocturnal mammal’s dwindling population.
“There were things that were affecting their forage – cattle grazing and fire and tequila harvesting,” Richardson said.
Conservation efforts such as the Manderscheids’ and modifications by tequila producers in Mexico to how they grow agave have gone a long way toward the species’ recovery, he said.
A 2015 lawsuit against Fish and Wildlife from the New Mexico Cattle Growers’ Association and other industry groups gave impetus to delisting of the species. Putting the bat on the endangered list restricted some aspects of cattle grazing, and ranchers for years had sought in and out of court to have the status of the bats reclassified – something Fish and Wildlife recommended in 2007 but did not propose until this year.
While a species’ delisting ends certain special protections under the Endangered Species Act, it also requires close monitoring for five years.
“We want to make sure we didn’t make the wrong decision,” Richardson said.
Tracking the Long-Nosed Bat
The Manderscheids’ hunt for their long-nosed seasonal visitors begins in the fall. Leaving south central Mexico in the spring, where the species is no longer endangered, the bats follow “nectar corridors” of blossoming plants to Southern Arizona.
The bats arrive in droves at the Manderscheids’ home on Tucson’s East Side by mid-September. They dive into four hummingbird feeders hanging from trees every night, until it’s time for their long-distance journey south in late October.
“We go through 10 to 12 pounds of sugar a week,” Gerry Manderscheid said.
The couple has fed and watched them closely to contribute written observations to a monitoring study involving several government entities and numerous volunteers.
Volunteers have monitored bat activity at Arizona hummingbird feeders for about a decade. Bats had been sighted previously in the city and as far as east the Chiricahua Mountains of Southeastern Arizona. Data submitted to the town of Marana via a website has helped shed light on the species’ foraging habitats and migration patterns, as well as sex and age composition.
In years past, the Arizona Game and Fish placed radio transmitters on bats captured at volunteers’ homes, which led to the discovery of new roosts.
Delisting the bats won’t affect plans to continue the monitoring study next year, said Janine Spencer, Marana’s point person on the project.
Ted Fleming, a biologist who has studied bats since the 1960s, analyzes the data collected by about 100 volunteers throughout Tucson and Southern Arizona. Although the bats usually do not begin dive-bombing hummingbird feeders until late summer, Fleming said the mostly female bats arrive in Southern Arizona as early as April.
“Females spend most of the summer giving birth and taking care of their young at maternity roosts in mines and caves,” in surrounding mountain ranges, he said.
Adult males only occasionally migrate here and the bats that predominate are young, usually a year or younger.
It’s not known how the bats first detected and took a liking to hummingbird nectar, but research done before the study shows that a meager crop of agave flowers around 2006 may have been a factor.
And the bats keep coming. Fleming said the sweet liquid makes a nice supplement to their mostly plant diet of fruit and nectar.
“The thing that intrigues me is the speed with which young bats find places to feed in town,” Fleming said. “We still don’t have a handle on how they do that. We have no idea.
“But we do know that they’re traveling some 25 miles one way from their day roosts to get to our yards every night.”
Where Bats Hang Out
In the early years of the study, most bats fed on the east side of Tucson, where the Manderscheids live. Now the bats have spread throughout a much larger swath.
Fleming lives in northwest Tucson, where bats often dip their long tongues into the two hummingbird feeders in his yard.
One night during peak season, he and Richardson donned headlights and waited for bats to fly into a mist net stretched between trees, not far from the feeders.
The biologists soon snare the first of what will be several catches. Fleming carefully untangles the bat and the men measure and weigh it. Although the male bat fits snugly in Richardson’s hand, it’s considered a medium-sized bat among its close relatives. Like most young bats, it weighs just under an ounce and has short, velvety gray fur.
“As they get older, around the neck and the head and on their shoulders they start to lighten up, they get sort of a tawny, buffy, almost yellow color,” Richardson said as he softly stroked the bat’s head, then released it into the night.
Because they’re nocturnal creatures, and because of the years-long craze for vampire books and movies, the lesser long-nosed bats are often misunderstood.
“They’re not scary,” Richardson said.
Programs that involve citizens, such as the Tucson study, help people become familiar with bats, which serve important roles as pollinators.
“These bats often fly in groups,” Richardson said. “It’s not uncommon to see a group of six just swirling around in my yard. Other people have 20 or 30 in their yard. It’s just incredible.”
Bea and Gerry Manderscheid couldn’t agree more. They’ve grown quite fond of their stealthy guests.
“They’re just amazing creatures,” she said.
“The bats are just like any other critter that we have out in the back yard,” Gerry Manderscheid said. “You become attached to it. You feel the need to take care of it.”