18 Aug
2013

Posted in: Uncategorized
By Hugh    No Comments

While Some Count Sheep, Others Count Bats

When darkness falls, most people retire to the comfort of their lighted homes. Human bodies are programmed by circadian rhythm to seek rest when night comes, letting the creatures of the darkness – owls, opossums, bats – move through the shadows. We do not follow their comings and goings, and perhaps we do not want to know what they are doing out there. We prefer to let nature’s nocturnals take care of themselves.

But there is a quiet killer moving among the creatures of the night, one that may result in the annihilation of an entire species within the next few years. It finds them resting in their homes and wipes out ninety per cent or more of their population in one season. Almost nothing is known of the movements of this killer, much less how to stop it. And that is one reason that, while we settle into the fortress of our homes, Rhode Island Department of Environmental Management (D.E.M.) biologist Charlie Brown is readying nets to capture some of this killer’s potential victims – bats.

It’s a cool spring night in the Great Swamp Management Area in West Kingston. A green D.E.M. pickup bounces along the dirt path, kicking up dust in its wake. Perched in the back are Bill Kowal, a student researcher with Brown, and Jennifer Brooks, a former colleague of Brown’s and current director of the Wildlife Clinic of Rhode Island, the only clinic in the state which cares for sick and injured wild animals. The trio will spend the early part of the night trapping and banding bats.

The truck bounces to a stop in a meadow bordered by woods. To the left, the border parts to reveal a path, beyond which is a small pond. The path continues into the woods at the far end of the pond, making these spots a natural corridor for bats to use on their hunt for insects. It is here that the nets will be set for the capture. As they wait for twilight, the three set out the tools they will work with tonight: calipers for measuring the length of the wings, headlamps, leather gloves, and a small scale. In an odd but practical bit of improvisation, Brown breaks out a box containing toilet paper rolls. The bat will be placed into a roll in order to quiet it while it is weighed. The combination of size and weight will help the crew determine the sex, and whether it is pregnant.

RIDEM biologist Charlie Brown readies the nets for the bat capture.

As dusk falls, the team raises the nets and moves back to wait for the first capture. Rhode Island is home to several species of bats: Red, Silver Hair, Hoary, Long Eared, Big Brown, and Little Brown. The latter two are by far the most common. They feed on a variety of insects, including beetles, moths, and mosquitoes. While they certainly benefit their surroundings with mosquito dining, it’s a myth that the annoying insects compose a majority of a bat’s diet. It makes sense, after all: as an insectivore, one stag beetle will provide far more sustenance than one mosquito.

The first trip to check the nets reveals only a beetle. The nets are made of fine, strong material. When an animal, even one the size of a beetle, flies into it, the nets flex with the impact. Before the animal can bounce out, it becomes wrapped in the net, safe but hopelessly tangled until retrieved. It is important to remove the creature quickly, says Charlie Brown. “Large insects that become trapped in the net can alert the bats that something is wrong. They aren’t normally likely to sense the nets, but if there’s a large bug in it, the bats are likely to fly up and over the obstacle.” Brown must lower the poles holding the 20’x18’ nets in order to reach the unwanted obstruction. He removes it quickly and the crew returns to their posts.

After another false alarm, the team gets their first catch of the night. It’s a Red bat, a rust colored migrant that nests in trees. Brown gives Jen Brooks the chance to do the first tag of the night. She measures the distance from the elbow to the first digit, the thumb (the bones in bats’ wings are actually a part of their “hands”). Its weight reveals it to be a pregnant female, the first of several pregnant bats tonight. Brooks struggles a bit with banding the animal, made challenging because she must wear gloves for protection. Following DEM protocol, only those with rabies vaccines will be allowed to handle the bats. Rabies is an infrequent occurrence, but precautions must be taken.

Brown extends the bat’s wing, and Brooks successfully crimps the band into place. The location is chosen because the leg is too small to accommodate a band, and this choice will not harm the creature. After the measurements have been recorded, Brooks moves away from the truck toward a meadow. She raises her hand nearly overhead to release the bat. Unlike birds, which are often capable of quick vertical flight from the ground, bats are accustomed to takeoff from an elevated perch.

Even in this case, the bat seems confused, and in a funny, if creepy, moment, the bat begins to wander down the length of Brown’s arm toward her. It’s awkward for a second or two, but it ends when the bat gets its bearings and flies off.

This process will be repeated a half dozen times in the hours the crew is there. Pregnant females mostly, Big Brown bats and Little Browns. The difference between the two is, as one might expect, size; the bigger bats are roughly five inches in body length, their little cousins averaging two and a half to four. DEM is monitoring the habits and health of the population: are they reproducing? Are the numbers similar from year to year? Is there any change in the overall health? It’s a major undertaking in times when budget restrictions squeeze personnel, making frequent and wide ranging counts a struggle. In addition to the overall monitoring of each species, Brown is looking for signs of the deadliest plague ever to hit bats: white nose syndrome. To understand this, it’s useful to rewind to an earlier winter.

Bats are measured for wing length, weight, and are then banded.

White Nose Syndrome: Extinction for Bats?

In a cave in New York, a colony of bats, numbering in the thousands, is hunkered down to spend the winter. They likely have come from throughout New England. Despite wind and cold outside the cave, temperatures inside will remain around 40 degrees. The feeding that the bats have done all summer has built up fats in their bodies. Those fats will be their sole source of nutrition through the long winter ahead, but since they will be hibernating, their metabolism will be slow enough for the fats to last. The bats will remain in a kind of stupor for months.

At some point, though, a fungus forms on the face of a bat. The fungus seems to thrive in the humid environment of the cave. Geomyces destructans, with a common name White Nose Syndrome, begins to irritate the bat. It awakens from its hibernation, and begins to expend precious energy and body fats in trying to scratch the infection. It begins to fly around the cave in a futile search for relief. In the meantime, the disease begins to spread throughout the cave. More bats awaken and react to the syndrome. The first bat infected, exhausted and starving from expending energy outside its normal time, drops to the floor of the cave and dies. Others will follow. By the time spring arrives, ninety per cent or more of the population will be dead.

This pattern has been repeating itself in hibernacula (dwellings where bats overwinter, including caves and mines) at least since the winter of 2006 – 2007. The infected areas encompass 19 states, according to a study of the 2010 – 2011 hibernating season by US Fish and Wildlife (USFW). Further, USFW estimates that over 5.5 million bats in the Northeast and Canada have fallen victim to the disease. In fact, it is only recently that scientists have even discovered the fungus.
Efforts are currently underway to fight the disease, but there does not seem to be a clear direction. Scientists have yet to determine the origin of the disease: is it transmitted through humans exploring the caves? Is it an environmental issue caused by people? Or is there some other source? Until some of these questions are answered, all that can be done is to stand by helplessly and watch the possible extinction of one or more species, including the Little Brown bat and the Big Brown bat. The latter two are often found in the nets set out by DEM biologist Charlie Brown, and would have a big impact on Rhode Island.

The remote building in Richmond, RI that houses a colony of bats.

Counting the Population: so far, so Good.

Eight weeks after the early June bat captures, the DEM crew is out again. By this time, the females have had their “pups”, and those that have survived have learned to fly. Tonight’s mission is to count, rather than capture the bats. The location is a building in a remote area of Richmond, where human incursions are infrequent and food is easily accessible. Back in the spring, scientists counted about 180 bats leaving the roost at dusk. The count is referred to as “pre-volant”, meaning the pups have either not been born or are incapable of flight. Those numbers form a base on which to determine the success of this colony.

Tonight, student researcher Bill Kowal is back to oversee the count, joined by two other DEM workers. The nearby water means there is a good supply of food for the bats, and DEM has been monitoring this location for some time. Of course, there are likely many other roosts around the state, beyond the personnel availability of DEM, but this one has proven to contain a regularly populated colony, hence its place in the count. Three people armed with clickers will monitor known exits from the building, and the results will be combined later in the night.

While this method of counting is low tech, it would be wrong to assume that all monitoring is so simple. Kowal shows off a device known as an ultra sonic detector. Not much bigger than an iPhone, the detector picks up bat calls imperceptible to the human ear. The calls are converted to mp3 format, and sophisticated software matches them to a particular species. This allows scientists to determine which kinds of bats are in the area, even when conditions make it difficult to make a visual identification. Kowal explains that DEM does numerous surveys with the detector in use as a driver cruises a specific area. Although it is not as thorough as a capture or count, the data still makes important contributions to the base of knowledge that includes which species are likely to inhabit a given area.

The team sprays themselves liberally with bug repellant and takes their places on the perimeter of the building. A lonely, dilapidated gray structure, it has numerous tiny openings near the chimney and eaves that allow bat travel. Almost on cue, the first bat exits the building. Without the detector, the only sounds are the crickets and other quiet night creatures. But the ultra sonic detector picks up the clicking, chirping sounds that the bat makes as it exits in search of a meal, and it is this odd noise that begins to fill the night.

The next hour is filled with the clicking of counters and of bat sonar. While there are periods here and there where traffic slows down, for the most part the silhouettes of the tiny mammals flutter across the sky in an ongoing parade. When the actions slows, Kowal wonders aloud whether the roost has emptied for the night, only to have two or three more emerge. It will not be until at least five or ten minutes have gone by without a sighting that the observation will be called to a close.

When that time finally arrives, the team reassembles at the truck to tally the results. The count for the evening is 319, nearly double the pre-volant count taken in the late spring. This is a good sign for this colony, because it is likely that most of the pregnant females were successful in producing a pup. (The adult males will not roost with the pregnant females. They continue to roam the area, usually spending the night in trees, bat boxes or buildings.)

Student researcher Bill Kowal checks for bays in a box nearby the building.

“The exit counts are not exact as on any given night a number of factors might affect the count, (i.e. weather, number of observers, too dark to see, some bats stay inside, etc.) but is more of an index,” says biologist Brown. “In a perfect world we would do additional counts and be able to get a good average, but there are not enough nights in the short season.” Still, this is the highest result of any location in the state, and therefore is a positive sign.

The work done in banding, monitoring, and counting bats of various species will continue in the spring, when the cycle starts again. Bats in Rhode Island have yet to show signs of White Nose Syndrome, but that may be because the infected die before they’re able to return to the state. The process of counting will help determine how widespread the disease is as scientists throughout the US and Canada work to determine a way to combat the plague.

During the June capture, Charlie Brown reflected on the creepy reputation bats have, a reputation that raises hairs on the backs of necks and makes many people relieved to bar themselves indoors when darkness falls. One of the Big Browns captured struggles mightily against the handling, making a screechy buzzing sound that is clearly audible without the use of the ultra sonic monitor. “It’s too bad that the image people have of these guys comes from this kind of moment,” he says as the bat tries free itself by biting and screeching. “It only makes sense that this animal reacts this way to us at the moment, but they’re really just cute little guys who play a really vital part in the ecosystem. They really are just misunderstood.”