BATTY ABOUT AGAVE

Some Bats Have a ‘Sweet Tooth’

CACTUS LOVER A Mexican long-tongued bat with a 14-inch wingspan sips nectar from an agave flower with a long, bristlelike tongue. The migratory bats are most often found at 4,000-6,000 feet where they nest in caves and provide essential pollination for many cactus species. Although they range from the tropics to the American Southwest, they're listed as a Federal Species of Concern as a result of loss of nesting caves and human-caused changes in their habitat. Lesser long-nosed bats play a key role in the survival of large cacti and agaves, which they pollinate at night. The bats winter in the Mexican tropics but journey to Arizona with the summer cactus bloom-although early arrivers may also get a quick fix from hummingbird feeders.

FEEDER FRENZY Nectar-loving species share the feeding trough with hummingbirds BY CHARLES S. RAU

"It's a mystery," said the bird-lover examining his hummingbird feeders in Portal, located in the Chiricahua Mountains in southeast Arizona. "During the summer, every feeder I have tried leaked, evaporated or something overnight so that by morning they were all empty. Have you ever seen hummingbirds come to feeders at night?" The quizzical look he gave me called for an explanation. "Not the feathered kind," I replied."Bats are probably emptying your feeders," "Bats!" he exclaimed. "I thought bats only eat insects."

I explained that 70 percent of the world's nearly 1,000 species of bats do feed on insects and other arthropods, but one specialized group feeds on the nectar and pollen from the flowers of certain plants.

Of the 42 species of bats found in the United States, three such nectar-feeding species flutter along the Mexican border in southern Texas, New Mexico and Arizona. These bats migrate into the United States from fall and winter sites, primarily in Mexico, starting in late April and early May.

The Mexican long-tongued bat and the lesser long-nosed bat are the only two nectar bats found in Arizona. They inhabit deep desert canyons and areas of desert scrub. They emerge from their daytime roosts in caves and abandoned mines in the early evening to forage on the blossoms of saguaros, organ pipes, other large cacti and several types of agaves.

Some scientists have suggested that the organ pipes, saguaros and century plant agaves may have coevolved a kind of partnership with nectar-feeding bats through blooming strategies and flowers that accommodate the bats. For instance, their flowers fully open at night to produce pollen, nectar and scents that attract the bats.

While briefly hovering or landing on the flowers to lap up the nectar with their long, specialized tongues, the bats are liberally dusted with pollen. They then inadvertently spread that pollen to the next flower they visit.

Some giant cacti and agaves depend heavily on bats for pollination. Unfortunately, a decline in these flower-loving bats could reduce reproduction of agaves and large cacti, which would disrupt the Sonoran Desert ecosystem.

After periods of feeding, bats congregate in temporary roosts to rest and lick the pollen from each other's bodies. The pollen provides a vital source of protein, although they will eat occasional insects. The bats also feed on the ripening fruit of the saguaros and organ pipe cacti and thus help disperse their seeds.

These bats also have discovered another source of nectar. During nights from mid-April through September, they often sip the sugarwater from back yard hummingbird feeders.

A single bat can slurp up an ounce a night. With this figure, we might estimate local bat numbers. At one location in the Huachuca Mountains, approximately 435 bats have visited feeders and in one back yard in Portal, 375 in a single night.

Nectar bats seem to have better manners than most hummingbirds, sharing the feeders without chasing each other off. Hummers, by contrast, will stake a claim to a feeder and ward off all others.

During the bats' return migration south to Mexico, hummingbird feeders may provide an important food source. Bat populations appear to be highly variable due to changes in habitat and natural food sources. The lesser long-nosed bat is considered endangered in the United States.

So, if you live in the Southwest and have been puzzled about the overnight loss of sugarwater in your hummingbird feeders, you've probably got bats in your... backyard. Al Charles S. Rau is a biologist and nature photographer and, when not leading natural history trips in southern Arizona and Mexico's Copper Canyon, he resides near Portal.