THE FOREST CLASSROOM

Researching the Elusive Whip-poor-will

How Audio Recording Devices Assist in Data Collection

By Carrie Deegan

The Eastern Whip-poor-will is the kind of bird you’re more likely to hear than see, in part because they are nocturnal, actively flying and foraging for insects only after the sun has set. During the day they rest motionless on the ground or a tree branch, their mottled gray-brown plumage blending in seamlessly with bark or dead leaves on the forest floor. Save for almost stepping on one, you’re not likely to spot a Whip-poorwill. On still, moonlit summer nights, however, it is definitely possible to hear the repeating onomatopoeic whip-poorwill call ringing out across the landscape.

This auditory encounter, which I have had the pleasure of experiencing numerous times over the years, is unfortunately becoming less common.

Since 1966, data from the North American Breeding Bird Survey suggests that the Eastern Whip-poor-will has experienced a nearly 70 percent population decline across its breeding range from Maine to South Carolina and west to the Mississippi River. The Whip-poor-will is currently listed as a species of concern in New Hampshire, as well as in 21 other states. There are numerous factors contributing to this steep decline, but two of the biggest are habitat loss and reduction in food abundance (moths and other nocturnal insects), possibly due to pesticide use.

Whip-poor-wills are a bit high maintenance when it comes to habitat. They prefer mature mixed forests with little understory for nesting and roosting during the day, but they also require open habitats such as old fields, shrublands, and young forest in order to perform the aerial acrobatics needed to catch moths and beetles on the wing. Here in New Hampshire, and across the eastern seaboard, we’ve got plenty of mature forest. It’s the fallow fields and early successional forest landscapes that are ever more limited compared to 50 or 100 years ago.

Thankfully, some landowners are managing their lands for early successional forests for other species. A program run by the federal Natural Resources Conservation Service called Working Lands for Wildlife (WLFW) provides financial incentives for landowners to create areas of young forest through patch cuts (i.e., the removal of all trees in an area) of varying sizes. In New Hampshire and the rest of New England, the primary aim of the program is to create habitat for the New England cottontail, a native rabbit whose populations have also been in decline. Further south, the program is focused on creating young forest and shrubland habitat for the golden-winged warbler. In the past decade, hundreds of private landowners as well as land trusts and conservation organizations, including the Forest Society, have created tens of thousands of acres of early successional habitat for these two species from Maine to Georgia through the WLFW program.

Currently, a collaborative research project involving scientists from the University of Massachusetts, Indiana University of Pennsylvania, State University of New York College of Environmental Science and Forestry, University of Pittsburgh, and University of Maryland is trying to figure out whether the young forest habitat created through the WLFW program is also benefitting the Eastern Whip-poor-will.

In June, I met the project lead, Jeffery “J.T. ” Larkin, a graduate student in environmental conservation at UMass Amherst, at the Forest Society’s Hills Forest in Durham, N.H., to learn about the research. This spring, Larkin and his team installed more than 500 autonomous recording units (ARUs) on WLFW research project lands across 11 states in the Whippoor-will’s breeding range, including on the Hills Forest, where 5 acres of habitat were created for the New England cottontail in 2012. “It’s not easy stuff to walk through, young forest, ” Larkin admits as he pushes through brambles and a thicket of small birch to reach an

The nocturnal Whip-poor-will relies on its camouflage plumage to rest during the day in plain sight.

J.T. Larkin installs an autonomous recording unit called an AudioMoth to record whip-poor-will calls in Durham, N.H. Recording devices have gotten much smaller and less expensive in recent years, while recording quality has improved. At about $90 per unit, including batteries and accessories needed for installation, collecting bioacoustic data is now affordable for many researchers.

installation site. As big as a credit card, the ARUs are programmed to record audio of their surroundings at precisely the times that Whip-poor-wills should be calling. During periods centered around the full moon, which were from May 19–June 2 and June 17–July 1, the devices captured audio for about 3 hours each day at dawn and dusk. Why? Whip-poor-wills typically only vocalize regularly when the moon is full or near full. Unlike echo-locating bats, Whip-poor-wills are visual feeders and use the moonlight to catch their insect prey. They actually time their egg laying so that chicks hatch just as the moon is waxing towards full, giving them the ability to provide regurgitated insects to their chicks while the moon is large and bright in the sky. How cool is that?

Now that the recording periods are over, Larkin’s team is conducting their epic field effort in reverse, collecting all of the ARUs from Maine to North Carolina, and beginning to analyze the recordings. “It’s actually not as bad as it seems, ” Larkin says, when I ask him whose job it is to sit and listen through thousands of hours of auditory data. Using computer-based artificial intelligence developed by the lab of Dr. Justin Kitzes at the University of Pittsburgh, a “machine learning classifier” is able to recognize the unique auditory spectrograph created by an Eastern Whippoor-will song. The recordings are broken into 5 second clips, and the classifier scores each clip from 0 to 1, with 1 being the most probable match to a Whip-poor-will song. Larkin’s team just needs to listen to the highest scoring clips per site per day in order to verify the presence (or absence) of Eastern Whip-poor-will at that site. “The machine classifier is absolutely amazing, ” Larkin notes. “It’s more accurate than human listening, and it never gets bored. ”

For a bird like the Whip-poor-will that is extremely difficult to see but easier to hear, research using ARUs to capture audio signals makes perfect sense. This research field, bioacoustics, is rapidly evolving and Larkin believes it will revolutionize and dramatically alter the way field ecology is conducted in the future. Technology has improved tremendously in just the last few years, with more sensitive, smaller and less expensive recording devices and better analysis tools. The amount of human effort required to conduct field surveys that result in 60,000 hours of data over 500 widely spaced sites is staggering when it’s done by actual humans, but with remote ARUs it is achievable in a single field season with a few researchers. “Bioacoustic data also lends itself to collaboration, ” Larkin notes. “We put our ARUs out specifically for Whip-poor-wills, but they are also recording mammals—maybe coyotes howling, insects like crickets and katydids, frogs…really anything that makes a sound. ” All that data can be archived and used by other scientists and researchers who are asking totally different questions about totally different animals, even decades or centuries into the future.

For now, Larkin is focusing on the task at hand, and hoping to find evidence that Whip-poor-wills are actually using the habitats created by the WLFW program in significant numbers. Although these birds are in a precarious situation at the moment, Larkin is heartened by all the potentially prime habitat he has bushwhacked through this field season. “It’s awesome that groups like the Forest Society have managed these lands for animals that require early successional habitat. A lot of people don’t view forest management in a positive light or believe it’s just not good to cut trees. But there are great opportunities to create habitat for species that are plummeting—and we need to encourage more of that.

Carrie Deegan is the reservation stewardship and engagement director for the Forest Society.

Learn More:

Turn to page 12 to get the scoop on how the Forest Society is managing land at the Heald Tract for early successional forest.