Rigor Vitae: Life Unyielding

Friday, June 20, 2008

BAT APPRECIATION WEEK part ii

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. Last year, 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. 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, which raises many interesting questions. Preliminary findings suggest that immune functions of infected bats may be significantly impaired. Like Chytridiomycosis in frogs, White Nose Syndrome is 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"

4 Comments:

Anonymous D Smith said...

What an impressive amount of information you've managed to squeeze into the two chiroptera posts! Wonderfully thorough, given the space constraint, and a joy to read.
I'm a veterinarian who has been doing bat rehabilitation for the past few years, and I'm happy to see such a well-written overview of these unique animals. There is definitely a need for more public education about them.
Could you mention what your source was for the wind turbine data?

10:13 PM  
Blogger cpbvk said...

Thanks! I'm glad you found the posts to your liking. Here are those citations:
Cryan, P.M. & Brown, A.C. Migration of Bats Past a Remote Island Offers Clues Toward the Problem of Bat Fatalities at Wind Turbines Biol. Conserv. (2007), doi:10.1016/j. biocon.2007.05.019
Kunz, T.H., Arnett, E.B., Erickson, W.P., Hoar, A.R., Johnson, G.D., Larkin, R.P., Strickland, M.D., Thresher, R.W. & Tuttle, M.D. Ecological Impacts of Wind Energy Development on Bats: Questions, Research Needs, and Hypotheses Front. Ecol. Environ. 2007; 5(6): 315-324
Cryan, P.M. Overview of Issues Related to Bats and Wind Energy Presentation to the Wind Turbine Guidelines Advisory Committee Technical Workshop & Federal Advisory Committee Meeting; Washington, D.C., Feb.26, 2008

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