NEW YORK (October 27, 2016) The WCS’s (Wildlife Conservation Society) Bronx Zoo and Fordham University have announced the results of the first known published study of bats in New York City. The study provides evidence of winter bat activity in NYC and documents the migratory movement of Eastern Red bats and Silver-haired bats through the Bronx Borough. Since little is known about bat behavior in winter, the research results may prove valuable in determining bat migration routes and overwintering strategies.
To identify bat species and activity levels during the study, scientists acoustically monitored bat echolocations calls at four sites in the Bronx: the Bronx Zoo, Rose Hill Campus of Fordham University, the New York Botanical Garden and Hughes Avenue, in the Belmont neighborhood of the Bronx.
Bat activity was recorded passively using acoustic-recording devices (http://www.wildlifeacoustics.com/) placed on the rooftops of buildings at each site, and actively by conducting surveys using a handheld ultrasonic recording unit. The recorders are programmed to record the echolocation calls that the bats produce in flight in order to navigate and locate their prey. The recorded calls are then processed through a software program, SonobatTM, which identifies bat calls by species.
Insectivorous bats have call frequencies that typically range between 20 kHz and 60 kHz which is outside of the frequency of human hearing (20 - 20,000 Hz). To make the calls audible to people, they are converted to a lower frequency.
The initial study began in May 2012 and identified the presence of five out of a possible nine species found in New York state: Eptesicus fuscus (Big Brown Bat), Lasiurus borealis (Eastern Red Bat), L. cinereus (Hoary Bat), Lasionycteris noctivagans (Silver-haired Bat), and Perimyotis subflavus (Tri-colored Bat).
"When we first began this project, we had no idea what we might learn about bats here in the Bronx,“ said J. Alan Clark, Associate Professor at Fordham University’s Department of Biological Sciences. “The results from our study are both surprising and exciting."
Results indicated that all five species of the night-feeders were present at all four Bronx sites, with the majority of recorded activity coming from Eastern Red bats (comprising 62 percent of identified passes of active surveys). “Tree bats,”— foliage-roosting migratory species—were represented by Eastern Red bats, Hoary bats, and Silver-haired bats and accounted for 70 percent of passively recorded calls. Activity was also recorded for these species during the winter months (December thru February) and revealed greater activity on nights with higher maximum daily temperatures. The other species identified during the study hibernate in caves during the winter and use tree cavities and buildings as roosts in summer.
The authors indicate that the increase in July of Eastern Red bat activity, followed by a peak in August and sharp decline in September suggests migratory movement through New York City as this pattern is consistent with acoustic surveys collected in the Midwest and East Coast in studies by others. In addition, an increase in Silver-haired bat activity occurred in late October—consistent with the timing of coastal migratory movements for this species.
The initial study was published in June of 2016. Since this initial survey, the study has continued at the Bronx Zoo in order to monitor year-round bat activity in the park and to identify any changes in patterns of call activity that could occur as a result of environmental factors. Additionally, the study has been expanded to include acoustic bat surveying at the three other WCS parks—Central Park Zoo, Queens Zoo and Prospect Park Zoo—using the same monitoring methods. Initial results from the on-going surveys reveal that the same five species occur in these three boroughs as well, although the call composition are represented by different species at each park.
“The results of our studies are particularly exciting as they show that within one of the largest megacities like NYC, there are sufficient green spaces available to provide habitat for bat species and other wildlife,” said WCS Bronx Zoo Curator of Mammals Colleen McCann.
Research of bats in North America has increased substantially in recent years. This is due in large part to a host of threats facing bats and the ecosystem services— such as insect control—that they provide. Among those threats are White Nose Syndrome (a fungal disease responsible for catastrophic losses of bat populations in eastern North America), impacts from wind turbines, roost disturbances, habitat loss and more.
While the project has contributed to the knowledge of bat ecology, the scientists say that additional surveys are needed. They recommend continued year-round recording combined with mist-net surveys, harp trapping, and active recording in a variety of landscapes to gain a fuller picture of the bat species assemblage in NYC.
To read more on the study and its findings, please see:
Bats in the Bronx: Acoustic Monitoring of Bats in New York City. published in Urban Naturalist. Authors include: Kaitlyn L. Parkins, Michelle Mathios, and J. Alan Clark of Fordham University; and Colleen McCann of WCS.