Volume 11, Issue 2, Summer 1993

Arizona's Night Visitors

In several small communities in southern Arizona, hummingbirds aren't the only dinner guests at the feeders . . .

By Lee, David S., Clark, Mary K.

In several small communities in southern Arizona, hummingbirds aren't the only dinner guests at the feeders . . .

by David S. Lee and Mary K. Clark

Nestled at the base of the Chiricahua Mountains in southeastern Arizona lies a small community where there are almost as many hummingbird feeders as residents. For some of the people of Portal, maintaining the feeders is a major part of their daily ro utine. Over 13 kinds of hummingbirds have been documented from the area. Residents not only know who has which species visiting their feeders, but they also know what time of day the rarer individuals show up.

Some 15 years ago, something began draining the bird feeders at night. Speculation about who the culprits were ran from ring-tailed cats to raccoons, but people who stayed up to watch their feeders quickly discovered that the night visitors were bats. Emotions were mixed among those who had set out the food for hummingbirds. Some wanted to discourage the bat freeloaders and started filling their feeders only in the morning. Others, fascinated by the nectivorous bats, repositioned feeders near porch lig hts so they could better observe their nocturnal guests.

The people of Portal soon learned the phenomenon was not unique to their community. In the Huachuca Mountains, the range to the west of the Chiricahuas, nectar-feeding bats had also been coming to hummingbird feeders at the Nature Conservancy's Mile-Hi Reserve in Ramsey Canyon since 1978, the same year they were reported in Portal. Residents of both areas now regularly observe bats at feeders during the warmer months. Dr. E.L. Cockrum, a professor at the University of Arizona, has also documented similar visitations in the Santa Rita Mountains and at several other locations.

We first heard about this phenomenon from our neighbors when we were building a cabin in the Chiricahuas several years ago. Sally Spofford, a long-time Portal resident, told us that 15 to 20 of her feeders were emptied nearly every night between late June and early September. The Spoffords have seen as many as 40 bats at a time. Based on this and knowledge of the amount of food consumed by captive bats, we believed that hundreds of bats might be visiting feeders nightly in some areas.

Eager to see the nectivorous bats, we placed a feeder under the eave of the cabin and were impressed that the bats found it only a few days later. We were also surprised to see them since no blooming Agave, or other plants known to be frequented by these bats, were in flower in the vicinity. Although our closest neighbors had maintained hummingbird feeders for several years, these were over a quarter of a mile away.

Only three species of nectivorous bats (Leptonycteris nivalis, L. curasoae,* and Choeronycteris mexicana) reach the United States at the northern extent of their range, and only two of these (L. curasoae and C. mexicana) are found in Arizona. We determined that both of these species were visiting our feeder. L. curasoae, lesser long-nosed bats, are large and pale. C. mexicana, Mexican long-tongued bats, are slightly smaller and noticeably darker.

Lesser long-nosed bats come to our feeder in groups of six or eight with as many as four hovering around at one time. They always approach from below, flying up from near the ground. Orienting upward from the corner of the cabin and along the porch railings, they hover four to 12 inches away from the building, flying up and down, apparently examining everything. Even though they are aware of our presence, they continue to feed with us standing as close as a foot from the feeder. Sudden movements cause them to fly away, but they usually return in less than a minute. After drinking, individuals dart off horizontally in various directions, though they always return in groups.

We have since learned that foraging behavior of lesser long-nosed bats has been studied by Dr. Donna J. Howell. She found that individuals avoid interference by taking turns, circling the plant in an orderly fashion. Groups at our feeder stayed for about five minutes, with individual bats staying for only a few seconds; 10 to 20 minutes later a group would be back for more.

Our neighbor, Boots Deiss, captured on film what we could only imagine from our brief observations at the feeder; the bats were so fast we could only guess that they were actually drinking. Photographs clearly showed two or three bats feeding simultaneously from different openings in the feeders. Other pictures showed the bats as they flew away from the feeders with their tongues protruding and tight round bellies distended. These photos and the steadily decreasing fluid level were ample proof that the bats were fueling up on the artificial nectar.

Mexican long-tongued bats came later in the evening than the long-nosed bats and usually arrived after the peak of group-feeding sessions. They too approached the feeder from below, but we did not see them engaging in the exploring activity of the long-nosed bats. We never saw more than one at a time, and it would stay longer, dipping into the nectar many times a minute, apparently also unconcerned by our presence.

Our first observations of the nectar-feeding bats were made between 8:00 and 9:30 in the evening, and they continued to feed until at least midnight. Neighbors have reported that bats return to the feeders throughout the night. Bob Morse, for many years an avid birdwatcher and now a bat watcher as well, has seen bats arrive at his feeders after dark and then roost in his garage between feeding bouts. For about 20 minutes they rest and groom pollen off their faces and necks before going out to feed again.

The pollen left on the bats' faces and on the feeders indicates that in the course of the night they are feeding from native flowering plants as well as hummingbird feeders. Pollen, their protein supply, is protected by a durable covering that cannot be digested by many animals. The nectar in a bat's stomach adds just the right carbohydrate concentrations, which, with the aid of a special acid-secreting gland, break down the pollen's covering. At the same time, the plants provide the specific amino acids for the acid gland to function. Because of this combination these bats can digest a meal that is biologically off-limits to most other animals.

What we do not know is how heavily these nectivorous bats rely on the feeders for sustenance. Hummingbirds in zoos cannot be maintained indefinitely on sugar water, and those with unbalanced diets do not reproduce. To correct this, a new product has been developed for the long-range maintenance of hummingbirds in captivity,* and the balance of proteins and other supplements seems to meet all their nutritional requirements. Perhaps it would suit the bats as well, but this protein supplement is expensive, and we do not know of anyone using it.

Hummingbird feeders in southeastern Arizona present an excellent opportunity for study of America's nectar-feeding bats. Monitoring feeding stations could provide information on population status and movements, and such stations could prove to be an important management tool. For example, the winter of 1987-88 was unusually severe in the Chiricahua Mountains, and late accumulations of snow altered the foraging behavior of local wildlife. Collared peccaries (Tayassu tajacu) consumed a large percentage of the intermediate-age classes of Agave palmeri, a major late-summer food source for nectar-feeding bats in the Southwest. This resulted in local destruction of Agave, and it is likely that at higher elevations blooming-sized plants will be in limited supply for as long as the next decade. Artificial feeding stations may help these nectivorous bats survive this shortage.

There is some evidence that the availability of hummingbird feeders has already altered the behavior of these bats. The number of bats using feeders, as well as the number of feeders being visited seems to increase every year. While some of this is clearly an increase in local awareness of the bats, residents like Sally Spofford who have been watching the bats for more than a decade are seeing a clear increase in the quantity consumed and in the frequency and duration of visits.

In the past, the time of year the bats were in residence seemed to parallel the flowering period of the agaves. But information from the Spoffords and others indicates that hummingbird feeders may be influencing arrival and departure dates. Mexican long-tongued bats seem to be arriving earlier (early June), and a small number of lesser long-nosed bats remain in the area from late June through the first week in November. There is even one documented record of both species seen at feeders in February and March.

Use of hummingbird feeders by nectar-feeding bats raises many questions. Have bats become too dependent on the new and seemingly bottomless food source? Could this behavior increase their vulnerability to weather extremes by affecting normal migration patterns? Is the artificial nectar adequately fulfilling nutritional requirements? So far, the growing numbers of bats visiting feeders suggests no harm to bats. We can only guess how this new food source affects their role as primary pollinators of various desert plants.

Nectivorous bats may seem to be part of a surrealistic utopia running on flower power, yet even here there is no such thing as a free lunch. The dual specialization of the plants and bats has them well along a path leading toward total interdependence. Threats to either the plants or bats affect the future of both, thus increasing their mutual vulnerability. Information that leads to the development of effective conservation strategies is lacking for most bat species. Hummingbird feeders could provide an opportunity for much-needed study.

David S. Lee is curator of birds, and Mary K. Clark is curator of mammals, at the North Carolina State Museum of Natural Sciences. They are both BCI members and have long been involved in bat research and conservation.

* Formerly Leptonycteris sanborni.

* Available from Neckton USA Inc., 14405 60th St. North, Clearwater, FL 34620.

Above: A Mexican long-tongued bat approaches a hummingbird feeder for a drink. Its long slender tongue, which can extend up to a third of its body length, reaches all the way into the bottom of the feeder where it can reach the nectar.

Blooming agaves are the natural food for nectivorous bats in Arizona, and pollen left at hummingbird feeders indicates that the bats are still visiting the plants. Had the hummingbird feeder been another agave flower, it would have been pollinated by the bat. Bats get dusted with a liberal coat of pollen when they burrow into the flower to reach the nectar below.

After lesser long-nosed bats finish a meal, they rest and groom themselves, thereby ingesting the nutritious pollen left on their faces and shoulders.

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