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BATS OF THE ROCKY MOUNTAIN WESTNATURAL HISTORY, ECOLOGY, AND CONSERVATION
By RICK A. ADAMS
UNIVERSITY PRESS OF COLORADOCopyright © 2003 the University Press of Colorado
All right reserved.
A twitch, a twitter, an elastic shudder in flight And serrated wings against the sky Like a glove, black glove thrown up in the light And falling back -D. H. Lawrence, "Bat"
Few poets have attempted to portray the nature of bats. Usually glimpsed in fits and moments, bats may appear bigger than life itself, personifying mystery and the unknown. As perceived spawns of Satan, they undoubtedly raise havoc and in their wake disease and destruction follow. Misconceived and shrouded in mystery, these winged shadows of night challenge our senses and cause us to re-evaluate an otherwise seemingly rational natural world.
After centuries of disparaging imagery, many of the intensely negative views of bats are waning somewhat. In many communities bat mythology is slowly being replaced with factual information that proves more astounding and interesting than fabled tales of the crypt and the macabre. With education and outreach, conservation organizations and other groups have begun to reverse many of the age-old,contemptuous attitudes of humans toward bats, and the lives of bats have undoubtedly improved because of those efforts.
With advances in research technology, biologists are able to learn more about the secretive lives of bats, and as a result, many of our preconceived notions about their natural history have proven incorrect. Bats, as it turns out, harbor few diseases contractible by humans and, as mammals go, are exceptionally clean. Despite their generally small body size, bats may live as long as thirty-five years, most species give birth to only a single young per year, maternal care of the young is altogether indulgent, and they appear to be quite intelligent. Furthermore, bats are important to many ecosystems, devouring tons of insects per year, pollinating important plants such as saguaro and organ pipe cactus, and dispersing the seeds of many significant tropical plants. Composing about 20 percent of all living mammalian species, they are one of the most successful groups to have evolved, yet many species are critically endangered.
This book is about the bats of the Rocky Mountain West. More broadly, it is an invitation to better appreciate bats as intriguingly beautiful animals representing part of our diverse world rather than as unresolved mythical creatures of darkness. I anticipate that readers of this book will "pass the word" about the beauty of bats, thereby furthering public education and appreciation. The challenges are great in this task, even in the twenty-first century. I hope this work will provide a welcome contribution to public education about and conservation of bats for years to come.
The intended audience is both the layperson and the specialist. The scope of this book includes bats found in the Rocky Mountain states of Montana, Idaho, Wyoming, Colorado, New Mexico, and Utah, as well as Arizona, which is linked geologically and ecologically to the Southern Rockies via the Colorado Plateau. We begin here with a general discussion about the biology of bats, followed by a description in Chapter 2 of the landscapes of the region and how bats fit into them. In Chapter 3 I discuss the regional evolution of bats, and Chapter 4 covers bat populations and community trends, feeding strategies, and resource use. Chapter 5 explores the strategies, achievements, and future goals for the conservation of bats in the Rocky Mountain West.
A key to species begins the section on species accounts. A picture and distribution map is presented for each of the thirty-one species. The accounts are intended for use by specialists and laypersons alike. For the layperson, information on the natural history of each species is presented, whereas the specialist will find technical information on standard measurements, dental formulae, and subspecies distributions. In addition, sections on ecology and behavior and reproduction and development present data accumulated in the primary literature for the region. A glossary of terms is provided at the back of the book.
Appendix 1 provides short descriptions of worldwide and regional governmental and private conservation groups and their Web site addresses. My hope is that readers will use these as convenient references to stimulate their involvement with organizations promoting conservation of, and educational outreach about, bats. I also provide a table of the current conservation status of each bat species. Although the status of any given species in any given area may change as more data are gathered, these tables at least provide a marker for the various bats at the time of publication of this book. Appendix 2 offers a bibliography of government agency reports and documents, many of which, like bats, rarely see the light of day. I hope this is helpful in disseminating useful information to wildlife enthusiasts and academic biologists alike.
A POWERFUL MISUNDERSTANDING: DECIPHERING THE REALITY OF BATS
The great bat biologist Donald R. Griffin (1958) once stated: "Bats are such unusual creatures that some effort is required to think of them as actual animals living in a world of common sense and concrete reality." Bats are indeed mysterious to humans. Cloaked by the darkness of night, they remain elusive to our senses. Although direct encounters between bats and humans are relatively rare, those that do occur are frequently sudden and unexpected, thus imposing immediate discomfort and distress. On balance, however, bats are gentle, attractive mammals who are simply trying to make a living. Different they are; evil they are not. Intriguingly, bats occupy the extreme edge of "mammalness," being so different from us that our mind struggles against acceptance. As a group, they represent a branch of evolutionary change unmatched in character throughout the six-hundred-million-year history of vertebrates (animals with backbones). Initially drawn to bats by their mystique, people who delve into really knowing them realize quickly that the true-life story of our winged friends is astonishing, easily eclipsing their mythology.
As we begin the twenty-first century, our knowledge of bats has grown considerably since medieval times. Many of the ancient myths vilifying bats, however, infect human impressions still and, in many cases, are all that people know of bats. Continued ignorance is fueled by our own shortcomings in perceiving an elusive mammal whose natural history evolved along a very different "route" than our own. To us they remain ambiguous night shadows whose abilities once suggested possession of supernatural powers. Indeed, human fear of bats dampened even the investigative enthusiasm of naturalists and scientists; consequently, we have only scratched the surface of what we can learn from and about them.
Despite our limited knowledge of bats and their populations, it is abundantly clear that they are important to the health and stability of many ecosystems. Equally clear is the decline in bat numbers worldwide. In fact, on many continents, including North America, if conservation actions are not undertaken, some species may become extinct before much, if any, of their natural history is even documented.
HOW MUCH DO WE KNOW?
Scientific inquiry about bats dates back to antiquity. Nearly twenty-five hundred years ago Aristotle formally described the anatomy of bats, and in 1693 John Ray first categorized bats as mammals instead of birds, although he remained confused about their wings. Carl Linnaeus, who in 1758 began the formal science of classification with the publication of his book Systema Naturae, arranged the then known seven species of bats within the order Primates, along with humans, all other known primates, and colugos (flying lemurs). In the mid-1800s the anatomists E. Geoffroy Saint-Hilaire and Georges Cuvier proposed a new order for bats called Chiroptera (whose name is taken from a Greek term meaning "hand-wing"). For the first time, the taxonomic relationship between bats and other groups was finally established. However, the science of taxonomy and systematics typically does not disseminate their findings to the public at large, so misconceptions remained.
For example, outside the scientific community, bats continue to be confused with other animals or misconstrued in character, not only in English but, unfortunately, across many languages. One author writes about the linguistic juggling of the various words used for bats, uncovering the underlying conceptual miscues in the process. He writes:
The German word for "bat," Fledermaus, means "flying mouse," as does the Russian lyetuchya meesh. Although certainly the reference to flight is correct, bats are not at all closely related to rodents. In English, bats were referred to as nattabatta, "night bat," perhaps of Scandinavian origin. Aftenbakke ("evening bat") is Danish for bat, and reference is made using nattbacka ("night bat") in Swedish. Possibly, all of these names are traceable to the poetic Icelandic word for bat, ledurblaka, meaning literally "leather flutterer." The Italian pipistrello (hence the genus Pipistrellus) apparently evolved from the Latin vespertilio, perhaps from vesper, "evening," plus papilio, a curious word meaning both "moth" and "the soul of the dead." French gets it all wrong; chauve souris translates to "bald bat," mostly untrue, even for the most senior of individuals. Spanish miscues with murcielago, a corruption of murciegalo, "blind mouse," neither of which is true of bats (Armstrong 1995: 1).
Unfortunately, even today, many people still consider bats to be "flying mice." In reality bats are no more closely related to mice than are humans. We know from several hundred years of anatomical study, especially on teeth, and, more recently, using molecular techniques, that the living group most closely related to bats is the order Insectivora, which includes shrews and moles. As for the evolutionary origin of bats, details of anatomy give insight into ancestry. Although one of the most highly evolved of all mammals, bats retain ancestral anatomical structures that give unequivocal clues as to the origin of the "ledurblaka."
THE ORIGIN OF "BATNESS"
From where did such a spectacular mammal, with wings for cheating gravity and a voice allowing for navigation in complete darkness, originate? As someone once said, "One cannot choose one's ancestors." And as with most compelling evolutionary stories, the origin of flight in mammals stems from quite humble beginnings. But before I describe this one-time-only evolutionary event, perspective is gained by emphasizing the fact that true flight evolved a mere three times throughout the six-hundred-million-year history of vertebrates (Figure 1.1). All three skyward reaches occurred autonomously. Birds, bats, and pterosaurs do not share a common ancestor that had wings, thus their evolution of flight originated independently, in each case stemming from a unique series of momentary interactions between the genotype (within which mutation is the source of innovative form), evolutionary history (which determines who has what genes), and environment (which is the selective influence on gene products, i.e., form).
Pterodactyls (flying reptiles) were the first vertebrates to fly. They witnessed the dawn of birds, but saw their own demise during the Cretaceous extinctions that relinquished the dinosaur's grip on world domination. Only birds and bats winged on into recent times. Evidence for the dawn of birds is inscribed in one-hundred-million-year-old limestone sediment where fossils, such as the famous specimen named Archaeopteryx (as well as others), have been found. Having a horny bill while retaining a mouthful of teeth, Archeopteryx was built of two worlds, one reptilian, the other avian, marking an important transition in evolutionary history. Curiously, although we associate feathers with birds, the evolution of feathers occurred in a group of theropod dinosaurs that were ancestral to birds. Plumage, it turns out, graced terrestrial species before becoming airborne.
Bats were the most recent vertebrate group to evolve powered flight and the only mammal to venture down that road. Mammals themselves are descended from therapsids, an extinct group that manifested both reptilian and mammalian characteristics and are therefore referred to as "mammal-like reptiles." It is here, in this transitional stage between reptiles and mammals, that hair evolved. Furred forms thus preceded winged forms (as feathers preceded flight in birds) by almost 180 million years, which means that bats have existed for a mere 25 percent of the evolutionary history of mammals. Furthermore, although one might surmise that the ancestor to bats must have been a provocative beast, bats actually descended from a rather nondescript, arboreal, shrewlike mammal that lived inconspicuously among the dinosaurs (Figure 1.2). It was only after an asteroid impact extinguished approximately 60 percent of the Cretaceous flora and fauna, prompting a major resorting of life on earth, that these persistent, furry pioneers prospered. The ensuing mammalian radiations (explosions of species) changed the planet forever, and for the first time in evolutionary history, fur came to dominate scales in terrestrial environments. Within the following thirty million years, all the major orders of mammals evolved, and one of the earliest groups to emerge from a burned and devastated world were bats. From ignoble beginnings, bats came to witness firsthand the coming Age of Mammals, termed the Cenozoic Era. How the first protobat looked, we may never know. Natural selection, however, obviously favored a mammal capable of nocturnal flight, allowing access to an almost completely untapped food resource: night-flying insects. The profits gained from the evolution of night flight propelled one of the greatest mammalian radiations and success stories thus far known.
The success continues today, as illustrated by the more than eleven hundred species of bats living worldwide (there are fifty-two hundred species of mammals alive today, so bats comprise about 20 percent of all living mammalian species). It is sobering to think that all bats share a single ancestral spark ignited long ago perhaps at a time when Tyrannosaurus rex and other large dinosaurs thundered across North America, restricting our terrestrial ancestors to their burrows by day and leaving the darkness of night as the only safe time for activity.
THE STRUCTURE OF BATS
The skeletal anatomy of bats is quite unique in form, but is simultaneously composed of easily recognizable bones located in the same relative position as present in all mammals. In fact, the basic anatomy of mammals evolved almost four hundred million years ago at the dawn of the first terrestrial vertebrates, the amphibians. In bats, although the forearm, hand, and finger bones are long relative to body size, the forelimb of bats comprises the ulna, radius, metacarpals, and phalanges found in all vertebrate animals (Figure 1.3), except, of course, for the legless lizards known as snakes and the legless amphibians known as caecilians.
The wings of bats are their most conspicuous trait. Gracile and highly elongated hands and fingers support a thin, elastic membrane (the patagium) that extends from the shoulder, travels between the digits, and reconnects along the body's lateral edge (Figure 1.4). The thumbs appear deceptively small when compared to the other greatly elongated fingers, but they are actually in proportion to body size. Thumbs are not connected to the flight membranes and function well as mechanical hooks for climbing and for manipulating food in carnivorous and fruit-eating bats. The tail in most species is wrapped by a membrane (uropatagium) that stretches outward, meeting the legs at their inner surface. Functioning mostly as a rudder during flight, the uropatagium in some species is highly specialized for use in capturing flying insects. The unique interlacing among supporting bones, membranes, and flight muscles produces a dynamic composite that allows a bat to negotiate a right-angle turn in less than the length of its body, sometimes at flight speeds approaching forty miles per hour. Don't try such a move in your Cessna!
Excerpted from BATS OF THE ROCKY MOUNTAIN WEST by RICK A. ADAMS Copyright © 2003 by the University Press of Colorado. Excerpted by permission.
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