Rigor Vitae: Life Unyielding

Friday, April 13, 2012


The same factors that keep the average schlemiel oblivious to the bats around him make it difficult for the odd interested party to study and understand them; they live in a world to which we are deaf and dumb. Before night vision goggles could amplify ambient light and bat detectors convert ultrasonic calls to audible frequencies, bat researchers were relegated to observing their subjects leaving or returning to their roosts and collecting droppings and food waste below. The data collected were added to somewhat random information gleaned from trapping individuals at night, and the rest of the picture was by necessity speculative. Some species like the Spotted Bat (Euderma maculatum – above) of the American Southwest, long considered very rare, are probably less rare than hard to observe (although this species is one of the few in the U.S. whose echolocation call is audible to human ears). The gap is slowly being bridged, but mystery still reigns when it comes to bat behavior. Unfortunately, this makes it hard to assess, address, or even perceive a crisis when it hits, and it's hard to say whether the current decline constitutes the beginning of a crisis or not, but something's going on.

Being mostly small and delicate, bats are especially vulnerable to stress, injury and infection. Insectivorous bats are often exposed to pesticides, many of which have endocrine-disrupting effects. Frugivorous bats can also be exposed to agricultural pesticides when they feed on human crops, and in such instances are often subject to more direct violence as well. Bats reproduce slowly; a single pup per season is the norm. Of course, habitat destruction can be devastating. For some social bats, a small piece of real estate can be crucial to a large population. Over much of their range, the Pteropus bats of Asia, Australasia and Madagascar are hunted for food or as crop pests, and typically shun areas where they're disturbed by humans. Today, large Pteropus colonies are restricted to remote regions or small, uninhabited islands, like Pulau Kalong, a flat, one-mile-square, mangrove-covered atoll west of the Indonesian island of Flores. Nearly a quarter-million P. vampyrus roost here during the day, leaving each evening to forage on adjacent islands (below). Besides removing roosting and hibernating sites, deforestation diminishes insect populations and stresses individuals.

In much of the northern hemisphere, safety/liability fanatics sealed many natural caverns and mine shafts during the last century, lots of them in such a way as to prevent the entry of bats, destroying important roosts and hibernacula. Such was the case with Ezell's cave, between Austin and San Antonio, where a large colony of Cave Myotis (Myotis velifer) were inadvertently excluded by a gate in the late 1950s. Without constant bat guano enriching the cave's subterranean lake, the water's ecology became impoverished, resulting in a decline of its top predator, the Texas Blind Salamander (Eurycea rathbuni), and its honor of being the first species listed under the U.S. Endangered Species Act. Several attempts at reintroducing bats failed spectacularly, and no bats have taken the initiative to recolonize the place on their own, probably due to human activity in and around the cave. In fact, spelunkers have always been a bit of a scourge for bats, disturbing maternity and hibernating colonies. When aroused from hibernation, a bat's metabolic rate jumps, and when disturbed too many times it can starve to death. In recent years the caving community has begun to discourage its members from entering major roosts and hibernacula during crucial periods. It's difficult to establish the overall impact on a species when a colony abandons its digs, but human disturbance in caves appears to be a major factor in the decline of numerous species, including the endangered Gray Myotis (Myotis grisescens) and Indiana Myotis (M. soldalis).

Light pollution is another bat threat that's hard to quantify. Over most of the industrialized world, the night sky has changed remarkably. The effect this has had on nocturnal ecosystems is profound, but poorly understood. In the late '80s, a wooded area adjacent to my home was replaced with a well-lit supermarket. Over the next three years, the composition of nocturnal insect species in the area was completely rearranged. Exactly how these changes transmit to insects' predators isn't well understood, but important effects should be expected. A number of faster-flying bat species have learned to exploit streetlights and the insects they attract, while some other species seem to shun them.

Wind turbines have been vaunted as ecologically-friendly alternatives to coal-fired and nuclear power plants, but, as with any system, they have their down side, too. It's become apparent that in some situations, the frequency of bat collisions with these structures is far greater than chance would dictate. Of the 45 species of North American bats, 11 have been recorded as killed by wind turbines, none of them endangered. Of the recorded fatalities, over three-quarters belonged to three species: The Hoary Bat (Lasiurus cinereus), Eastern Red Bat (L. borealis) and Silver-haired Bat (Lasionycteris noctivagans). All three bats migrate long distances and roost in trees, Lasionycteris in tree cavities, and Lasiurus usually in foliage. More data are needed, but it appears that most bats are killed during the fall migration, and then mostly on still, overcast nights. To better understand the significance of this, let's look at the behavior of the best-known of these three species.

The beautiful Hoary Bat (above) is the most widespread, and over much of its range, the biggest bat in North America. Its sturdy foot-wide wingspan can carry it for amazing distances. It's the only bat to have successfully colonized the Hawaiian Islands, and it occurs on Bermuda and even Orkney Island, north of Scotland. A close relative was one of the few native mammals on the Galapagos, but it appears to have recently gone extinct. During the summer, males and females live separately, and many populations appear to consist solely of one sex, the females tending to concentrate in the east and the males in the west. A single female raises her pups each year in a group of spruce trees not far from my home. In September, migration and contact between the sexes begins, along with courtship behavior, including copulation and fighting between males. Hoaries may migrate singly or in flocks. Like many migrating birds, they seem to follow the Pacific coastline south, and it seems reasonable to expect migrating bats in general to follow shared flyways. The sexes live together during the winter, then separate for the spring migration. Females store sperm over the winter and ovulate in the spring, giving birth early in the summer. Lasiurus bats sport four mammaries instead of the normal two, and can give birth to as many as four, or in unusual cases, five, pups. The Hawaiian subspecies, L. c. semotus, is thought to have declined from habitat loss, and is listed as endangered by the U.S.D.I. The I.U.C.N. lists its status as indeterminate.

Courtship behavior probably has a lot to do with the huge spike of collisions during fall migration without a corresponding spike in the spring. Whether the increased mortality on overcast nights is related to increased migration activity or lower altitude of flight has yet to be established. Bats seem to be hit more frequently by turbines on tall towers, especially in wooded areas, but the available data are still rather poor. It is suspected that bats may be attempting to roost on turbines. Many fatalities seem not to result from a strike by the blade, but from rapid decompression from the vortex trailing behind it. At some sites, Mexican Free-tailed Bats (Tadarida brasiliensis) may be at special risk. Current research involving coating turbines with paint of varying UV reflectivity seems to indicate that a simple paint job could reduce mortality. As the nature of the problem becomes better understood, it seems likely that a safer wind farm regime can be devised.

In February 2006, a new and especially alarming bat threat was discovered. Bats in a hibernaculum near Albany, New York were found with a crust of white fungus on their face and wings. The fungus was originally identified as belonging to the genus Fusarium, a group primarily associated with plant disease, but including vertebrate pathogens as well. At the height of the Cold War, both the U.S. and Soviet Union conducted biological warfare research with Fusarium fungi. In 2008, it was determined to belong to another fungal family altogether, and was ascribed to the genus Geomyces. In 2009 it was identified as a new species: G. destructans. By that time, White Nose Syndrome (WNS), as it has come to be known, had spread to most of the known hibernacula in New York, and into Vermont and Massachusetts. Mortality of affected bats at these sites has been 90 – 97%, but it is difficult to gauge how many, if any, survivors make it through the summer. Each year has seen a rapid geographic expansion of WNS; its westward spread has crossed the Mississippi and it has ventured as far south as Alabama. The latter fact is surprising, since the fungus only thrives in cool temperatures. Whether the fungus is the cause of a fatal disease or just an opportunist associated with an unidentified pathogen is also unknown. Afflicted bats exhibit radical behavior change, including increased winter activity. They often fly about the cave entrance, even leaving it to flutter about in broad daylight on a frigid winter day. Not surprisingly, necropsied bats have shown depleted fat stores. The disease could be directly responsible for this, or it could be the result of increased activity and inability to find food, or both. Is the activity caused by hunger or vice versa? It's possible that the pathogen interferes with the bats' ability to thermoregulate. In the winter of '06 -'07, an infected bat was taken into captivity, fed up, and released in spring, which suggests that it may be possible for bats to fight the infection if their condition is sufficiently raised. Some articles have blamed global warming, but there is no basis for this. Within the affected sites, all cave-hibernating species have been found to be affected, except the Big Brown Bat (Eptesicus fuscus) and the Eastern Small-footed Myotis (M. leibii). The latter species, listed by New York state as a species of special concern, hibernates in different sections of the hibernacula, and work is underway to establish if they are infected; it's assumed that they are. Important populations of the endangered Indiana Bat (M. sodalis) are also afflicted. Eighty-five percent of the known population of this bat hibernates in 7 caves. Preliminary findings suggest that immune functions of infected bats may be significantly impaired. Some dead bats have been found without the fungus, and fungus has been collected from asymptomatic bats. In 2008, G. destructans was found on an otherwise asymptomatic Greater Mouse-eared Bat (Myotis myotis) in France, and a research team from the University of Winnipeg has just confirmed that the fungus indeed originated in Europe, where the endemic bats are far more resistant. Like Chytridiomycosis in frogs, which was also transported from abroad, White Nose Syndrome remains a darkened room with far more questions than answers, and the potential of real ecological devastation. Disinfection and general behavioral guidelines (similar to the ones established in 2007 for Chytridiomycosis) are being hammered out for biologists and spelunkers. Nine universities and a number of state and federal wildlife and health agencies are involved in studying WNS, along with a number of independent researchers. The U.S. Fish & Wildlife Service's Indiana Bat Recovery Team is overseeing distribution of funds.

According to the IUCN, nine bat species have recently gone extinct (six of them megachiropterans), 32 species (14 megachiropterans) are critical, 44 (9 megachiropterans) endangered and 172 (39 megachiropterans) vulnerable.
Thanks to Laura Ellison
upper: SPOTTED BAT (2008) acrylic on illustration board 20" x 30"
middle: Pteropus vampyrum photo by CPBvK
lower: HOARY BAT (1993) acrylic on illustration board 17" x 12"

Thursday, April 12, 2012


The United Nations Bat Convention an Bat Conservation International have deemed this the year of the bat, and this week "Bat Appreciation Week," which gives me a chance to update and recycle some old material. Few of us take notice of bats, but they're all around us. Aside from rodents, they comprise the biggest, most diverse mammal order (Chiroptera), with over a thousand species and a nearly global distribution. They're only absent from a few small, remote islands and the polar regions, and they often occur in huge numbers. At over 100 million, the Mexican Free-tailed Bat (Tadarida brasiliensis) is one of the US' most plentiful mammals, despite being restricted to the southern third of the lower 48. Despite their numbers, bats' nocturnal habits and mostly small size and secretive nature keep them out of sight and, for most of us, mind. In temperate latitudes, bats are small, insectivorous creatures that devour many tons of insects every night, but as one moves toward the equator, they become far more diverse in form and behavior. In the tropics, they have evolved to feed on fish, birds, and other vertebrates—even on blood, as well as fruits and nectar. Many tropical plants, like the Merinthipodium neuranthum feeding a pair of Lonchophylla robustum in the painting above, are dependent on bat pollinators. Many fruits, including Africa and Madagascar's iconic baobabs (Adansonia spp.) rely on fruit-eating bats to disperse their seeds.

Bats' dainty structure makes them exquisitely adapted for flight, but poorly so for leaving fossil records, and bat evolution is not well understood. The oldest known bat fossils, from early Eocene deposits in both Europe and North America, are quite similar to modern forms and don't likely represent the order's roots. Modern bats fall into two large suborders. The Megachiroptera comprises the family Pteropididae, the fruit bats, a group restricted to the Old World, including the biggest bats, the flying foxes (Pteropus spp. - above), whose wings can span a meter and a half. In all, there are 42 megachiropteran genera with around 173 species. The remaining 17 bat families reside in the suborder Microchiroptera. It was long assumed that both groups were derived from a common ancestor, but a recent and controversial theory, based on similarities between megachiropteran and primate brains, proposes that the two bat groups evolved flight independently of each other, spurring a lively and continuing debate—and that's about as far as I care to wade into those shark-infested waters. Whatever their phylogenic trajectory, the first proto-bats probably evolved from tree-dwelling gliders similar to the modern Colugo (Cynocephalus volans - below) of Southeast Asia, probably bats' closest living relative.

The largest microchiropteran family is Vespertilionidae, the vesper bats. This family of 42 genera and about 355 species is distributed globally. Typically small insectivores, vesper bats include most temperate zone species. The genus Myotis, with around 100 species belongs to this family. Aside from Homo, it's the most widely-distributed terrestrial mammal genus, with representatives on every continent save Antarctica, and as far afield as Samoa.

The most diverse family, Phyllostomidae, is restricted to the New World. This group includes the tongue-feeding bats of the subfamily Glossophaginae, like our friends Lonchophylla up top. These nectar eaters are important pollination vectors for many plants, including the crucial Blue Agave (Agave tequilana), from which tequila is manufactured. Other notable phyllostomids include the three vampire bats (subfamily Desmodontidae), with three monotypic genera, and the carnivorous Vampyrum spectrum (below), the largest New World bat, indeed the largest microchiropteran.

The painting below depicts a V. spectrum creeping through the foliage of a Saragundi tree (Senna reticulata) towards a group of roosting Smooth-billed Anis (Crotophaga ani). These bats prey heavily on birds, and anis, being social roosters and rather smelly and therefore easy to locate, are very common prey items.The fabulous-looking Old World horseshoe bats (Rhinolophidae) include two of the biggest bat genera, Hipposideros and Rhinolophus (below), with 51 and 69 species, respectively.

The afore-mentioned Mexican Free-tailed Bat belongs to the Mastiff family, Mollosidae, with 16 genera and 86 species. The family, whose tails extend well beyond the interfemoral membrane or patagium, includes some of the most social mammals with colonies that can number in the millions.
The emballonurid, or sac-winged bats comprise 12 genera and 48 species, with pantropical distribution. Most members sport a glandular wing sac near each shoulder that secretes a strong-smelling, reddish fluid. The remaining twelve bat families are small ones, with less than ten species apiece. They include such favorites as the monotypic Craseonycteridae from Thailand, whose sole species, Craseonycteris thonlongyai, is possibly the world's smallest mammal, and the ditypic Noctilionidae, whose two Neotropical species (Noctilio leporinus is pictured above) are common throughout the American tropics, including the islands of the Caribbean, wherever there is still water. Remarkably specialized for catching small fish swimming near the water's surface, they eat little else and show no capacity to forage in any other way. These creatures' sensitive hearing can pinpoint the tiny ripples made by fish swimming near the surface surface by echolocation, then, dragging their long claws beneath them, they rake up their prey, eating it on the wing. The sight of one of these large bats fishing on a foot-and-a-half wingspan, its talons raking the glassy expanse of a moonlit blackwater lagoon, is not soon forgotten. There's our glimpse of general bat ecology and biogeography. The next post will address their current decline.
upper: MARKEA NEURANTHA (1995) acrylic on illustration board 30" x 15" (note--this plant was re-designated as Merinthopodium neuranthum a couple of years after I painted and named this piece.
All photographs by CPBvK; Locations (in order): Maraonsetra, Madagascar; Nusa Tengara, Indonesia; Sarawak, Malaysia; Fortuna, Costa Rica; Flores, Indonesia
middle: SPECTRAL BAT & SMOOTH-BILLED ANIS (2012) India ink wash on Arches paper 22" x 16"
lower: FISHING BULLDOG BAT (1997) acrylic on illustration board 15" x 20"