The Pettersson D500X ultrasound
recorder looks a bit like an old-fashioned transistor radio with square
buttons, a modest display screen, and a built-in microphone. Yet despite its
unimaginative appearance, the device can detect the echolocation sounds made by
bats and, with the help of software that identifies the bat species involved,
is helping scientists reveal new information about the movements and migration
behavior of local bat populations.
Biologists at the Rhode Island
Department of Environmental Management and the University of Rhode Island have
deployed the bat detectors throughout the state this year in a variety of ways.
DEM wildlife biologist Charles Brown, for instance, mounts one on the roof of
his truck as he periodically drives five routes around the state to look for
trends in bat numbers and to compare his findings with those driving similar
routes in other states. He also places the
devices in various state wildlife
management areas to scout for locations to trap bats for more detailed studies.
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| Silver-haired bat (The Nature Conservancy) |
The most revealing use of the
detectors, however, has been as a way of monitoring bat migration through the
state.
“Not a lot is known about bat
migration, so we’re just trying to figure it out for various reasons,” said
Brown. “There’s a great interest in wind turbine development – turbines kill
hundreds of thousands of bats every year – so we want to know when they migrate
and where.”
Brown selected several locations
along the Rhode Island coast to place the detectors for long-term monitoring of
bat movements. Every week since early August, he has downloaded the data from
the detectors to learn what he can about the seasonal movement of bats.
“Much like birds, they migrate at
the same times and during the same general weather patterns,” Brown said. “They
head south until they hit the coast and then they follow the coastline. There
are certain locations where you’d expect them to pile up and be concentrated,
like Point Judith, Sakonnet Point, Beavertail, Brenton Point.”
While he admits he didn’t know what
to expect with the data he was collecting, he was somewhat surprised to learn
that bat migration appears to begin much earlier than he anticipated.
“We’re seeing pulses of activity
beginning in August, and I’m not sure that’s well known,” Brown said. “But
they’re opportunistic animals, so when they get the right weather conditions,
they probably just figure that this is a good time to go.”
Bat migration is believed to
continue through October and early November.
The only difficulty with the bat
detectors is that it’s impossible to know how many bats are being detected.
“It might detect a thousand calls in
one night, but we don’t know if it’s a thousand bats flying by or one bat that
flew by a thousand times,” he said. “There’s no way to differentiate it.”
Most of the bats Brown has detected
are red, hoary and silver-haired bats – collectively called tree bats – all of
which migrate south each fall. He also occasionally detects small numbers of
little brown bats that migrate north to hibernate in caves and mines in New
Hampshire and Vermont. Little browns have declined dramatically in the last
decade due to the effects of white-nose syndrome, a fungal disease that has
killed millions of hibernating bats throughout the Northeast. Big brown bats,
many of which spend the winter hibernating in Rhode Island, are also detected.
URI Professor Peter August has
conducted similar monitoring of bat migration at Napatree Point in Westerly
using the same kind of detector, and his results mirror Brown’s.
“While in mid-summer I’d have a couple hundred
bats passing by in a week, starting in August I’ve been getting a couple
thousand in a week. The activity has really peaked.”
He plans to continue to monitor for
bat activity at Napatree until he detects no bats at all.
“Nothing brings great clouds of bats
to Napatree in the summer, which is what I expected,” said August, who earned
his doctorate studying bats in South America. “It’s not an active summertime
habitat, but it changes this time of year. We have lots of bats moving around
now. Our migratory bats are headed south, and our hibernating bats are moving
around the area looking for places to hibernate.
By combining data from the detectors
with anecdotal information from other sources – like surfers who report large
movements of bats at sunrise and wind turbine owners who report dead bats at
the base of the structures – Brown and August are piecing together the story of
bat migration in Rhode Island.
“With all this information, we’re
finally getting a better sense of what’s going on here,” Brown said. “The
information we’re getting will give us a better sense of how big a problem wind
towers will be for our bats. As more and more wind turbines pop up on the
landscape, it’s probably going to be a problem. It’s already a problem. And
then we’ll have to question whether the mortality is sustainable.”
This article first appeared on EcoRI.org on September 27, 2017.
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