Shhhhhh! Bats Wintering.
Please cave Softly and Quietly.

James B

In Flagstaff, we had our first snow of the year on October 16th. Many bats of north-central Arizona are on the move, and some have already departed. Data are scarce-virtually all published studies of bats in our area were conducted in the warmer months of the year, when academics are on their summer breaks. But based on our limited information, let us consider the impacts of caving on our wintering bats.

Several of our bat species disappear from their summer roosts, and we have no idea where they go. Others make local migrations to warmer climes within Arizona. Some populations of one Arizona bat, the Mexican Free-tail Bat, Tadarida brasiliensis, migrate long distances to Sonora, Sinaloa, and perhaps farther south in Mexico. This apparently applies to T. brasiliensis in most of Arizona, including the great roost in Eagle Creek Cave, Greenlee County, and our own Mexican Free-tails in the Prescott-Verde Valley-Sedona-Flagstaff region. I have never seen a hibernating Mexican Free-tail Bat in Arizona. In adjacent California, however, at least some Mexican Free-tails stay put in winter. The boundary between the migratory and non-migratory groups is poorly understood, but this boundary appears to pass through the western portion of the region covered by our Grotto. Mexican Free-tails are present in the western Grand Canyon in winter, where they apparently feed on warmer nights. I saw plenty of active Mexican Free-tails in Bat Cave, Mohave County, on January 4th, 1987. Mexican Free-tails are famous for the massive cave roosts they form here in the American Southwest, such as those at Carlsbad and Bracken Caves, but they also occur in smaller groups, and mix widely with other species. This small bat has a distinctive look, sound, and smell. Its fur is short, dark, and velvety. Its face is vaguely doglike, with its ears nearly joined above its forehead. Its wings are long and narrow. Most importantly, its tail extends well beyond the membrane between its hind legs (hence its name). The Mexican Free-tail is responsible for most or all of the commercially-significant guano deposits in our area. Its turds are tiny, and its musk is potent. Many of you have smelled it in the little caves used by prehistoric Native Americans in the Verde Formation bluffs near Beasely Flat, downstream from Camp Verde. I would enjoy hearing about your observations of its distribution and habits in our area.

In the bottom of the Grand Canyon, you will see our smallest bat, the Western Pipistrelle, Pipistrellus hesperus, emerge from rock crevices in cliffs to feed on warmer nights of the winter. I rarely see "pips" in caves in northern Arizona-they seem to prefer small crevices. In Grand Canyon, many of you are aware that this bat even flies in the shadows in late afternoon, one of the few places where flying bats can be seen in the daytime in the United States.

Finally, this brings us to the bats that winter in the caves here in the high country of northern Arizona. While caving in the colder months, if you look around carefully, you might see several bat species, some of which are comparatively rare. The take-home message is that if we explore caves at all in winter, we should do so QUIETLY, and "SOFTLY." Typically, these animals are in a deep state of torpor, with their body temperature depressed, and their metabolism nearly shut down. This is unlike our own sleep or the winter sleep of bears, where the animals remain warm. Hibernating bats in our area are deeply dependent on their fat reserves. Disturbances, such as cavers talking or shining lights on the animals, can cause the bats to arouse. Torpid bats might take many minutes to several hours to fully awaken, and you might be long gone by then, and not notice. Still, these inappropriate awakenings can deplete their fat stores, and kill them before the warmer weather returns.

I will save the bat tutorial for a later date, but look for these wintering bats in northern Arizona:

TOWNSEND'S BIG-EARED BAT, Corynorhinus (nee Plecotus) townsendii, has spectacular, large ears and big lumps (pararhinal glands) on its snout (rostrum). If deeply torpid, the ears will be curled up and laid back, vaguely resembling rams' horns. This species winters in some remarkably cold, exposed sites in mines and caves in our area. They even use snow-bound caves well above 7,500 feet elevation. You will see them sitting singly or in pairs on flat surfaces of walls or ceilings. Some people refer to the genus MYOTIS as the "little brown bats." These are handsome little animals, and might winter on open surfaces, or in holes and crevices, with only their faces exposed. Bats are not rodents, so forgive me if I describe the genus Myotis as a little "mice-with-wings." Their faces are relatively plain. Most bats you see in Arizona caves belong to this genus. Some species are difficult to distinguish in the field, even to experts. The similar BIG BROWN BAT, Eptesicus fuscus, looks like an overgrown Myotis.

Disturbance of wintering bats by cave explorers has undoubtedly contributed to the declines and local extinctions of many bat populations around the world. Some roosts should probably be closed to all entry in the colder months. If you must go caving in the winter, please, please "CAVE SOFTLY, CAVE QUIETLY." ^x^

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