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The stealthy, winged creatures arrive at night, seeking backyard hummingbird feeders. The nectar is meant for avian visitors, but in the twilight hours, it is lesser long-nosed bats that feast on the sweet liquid.

They take over Marilyn Hanson’s feeders shortly after sunset, pausing to speed-sip the nectar and vanishing as swiftly as they appear at her suburban Tucson, Arizona, home. By morning, the feeders are drained. “I make sure I’ve always got a half-gallon of sugar water in the refrigerator,” she says.

The birder and retired biology teacher is among a cadre of community scientists who refill their feeders every morning and keep track of bat activity around them as part of a long-term study of their nocturnal summer visitors. Their observations have played a vital role in an effort that led to the removal of the species from the endangered list—the first bat ever delisted due to recovery—and continue to contribute to its conservation.

The volunteers start seeing bats in their yards as early as July and bid them farewell in late October, a time of year when bats are portrayed as hair-raising, blood-sucking creatures. “Bats are a traditional symbol of Halloween, but there’s a lot of misunderstanding about them,” says biologist Ted Fleming, a retired University of Miami biologist and lead collaborator in the project. They control pest insects, pollinate crops, disperse seeds, and provide nutrient-rich fertilizer with their guano, Fleming notes. “For me, it’s easy to make a case for the importance of bats economically as well as ecologically. But overcoming the fears and the myths is another matter.”

When people interact with bats, the encounters can shed light on the true nature of the creatures and help dispel misconceptions, says Fleming, who has studied bats since the 1960s. “The more people who get involved and learn about bats, the better their appreciation of them.”

Unlike other bat species that eat insects, lesser long-nosed bats (Leptonycteris yerbabuenae) feed solely on flowers and desert fruit. Each spring, they migrate hundreds of miles, following a northbound “nectar trail” of blossoming agaves and saguaros, which they also pollinate. Tens of thousands of them settle in southern Arizona. As early as April, caves scattered across the desert transform into maternity roosts where females give birth and raise their young. By early fall, clusters of mostly young bats and some adult females take over hummingbird feeders to fuel up for their journey back to Mexico.

In 1988, fewer than 1,000 lesser long-nosed bats were thought to remain at 14 known roosts, prompting the U.S. Fish and Wildlife Service (FWS) to list the species as endangered. Scientists blamed the bat’s frail state on habitat loss, human disturbance in the caves and mines where they roost, and harvesting of agave for tequila production before the plants bloomed, which took away a key food source for the bats.

Although researchers had a sense of what was causing the long-nosed bat’s decline, efforts to recover the species faced a significant hurdle: Scientists lacked some basic information needed for effective conservation. Enter the community scientists.

Lesser long-nosed bats were occasional visitors to hummingbird feeders on Tucson’s east side, but as a result of a poor agave crop in 2006, they began appearing more widely at feeders across the city and its suburbs. Starting in 2007 the FWS and partners to record when bats visit their homes, measure nectar levels in the evening and again in the morning, and submit their data to the Arizona Game and Fish Department. To complement the feeder data, the wildlife agencies set up mist nets in participants’ yards to confirm the species—Mexican long-tongued bats also visit the area’s feeders—measure the bats, and, in some cases, to fit them with temporary radio transmitters to track their movements and pinpoint roost sites. Today more than 100 volunteers take part in the program.

Their data provided valuable insights into the foraging habits, age and sex composition, and movements of the nectar-loving mammals. The feeder observations helped scientists pin down the timing of bat migration, for instance. And the tagged animals led researchers to previously unknown roosting sites, revealing that some bats travel up to 25 miles each way from their roosts to the hummingbird feeders.

While Hanson and other community scientists were minding their feeders, agencies and organizations on both sides of the border were busy educating the public and protecting the bats’ habitat. In Mexico, for example, partner groups reached out to tequila and mezcal makers, whose industry relies on the pollination services bats provide. Now many producers earn a by leaving a portion of their agave unharvested. In the United States, federal agencies that manage bat habitat have created plans to conserve the agaves, saguaro, and organ pipe cacti bats need for foraging. They’ve also worked with Bat Conservation International to install gates to keep people out of caves and abandoned mines where colonies roost.

By 2018 scientists had increased their estimate of the lesser long-nosed bat’s population to 200,000 individuals at 75 roosts on both sides of the border—enough to . The rebound was a vote of confidence in the ongoing conservation efforts, but it also reflected the more complete picture of the bat’s distribution and numbers that the hummingbird feeder data helped to paint. Mexico removed the species from its threatened list in 2015.

While the project has yielded many important insights, the bats still hold secrets that flummox scientists, such as what paths they travel from their roosts to people’s yards, how they find hummingbird feeders, and why they keep returning for several hours after emptying them.

When the researchers return to Arizona next year, Fleming and his collaborators plan to continue studying the bats using a sophisticated remote-tracking system that should make it easier to record the bats’ movements. But the project will still rely on the low-tech contributions of its dedicated volunteers. As she has for a decade, Hanson will do her part by making sure her hummingbird feeders are full when the nighttime visitors return in the spring.