Andrea M. Simmons, andrea_simmons@brown.edu
Charlotte R. Thorson, charlotte_thorson@alumni.brown.edu
Madeline McLaughlin, madeline_mclaughlin1@brown.edu
Pedro Polanco, pedro_polanco@alumni.brown.edu
Amaro Tuninetti, amaro_tuninetti@brown.edu
James A. Simmons, james_simmons@brown.edu
Brown University
Providence RI 02912

Popular version of 2pPPa1 – Echolocating bats modify biosonar emissions when avoiding obstacles during difficult navigation tasks
Presented Tuesday afternoon, December 2, 2021
181th ASA Meeting, Seattle WA
Click here to read the abstract

Bats use echolocation, an active biological sonar, to find their way in the dark. By broadcasting trains of intense ultrasonic sounds and listening to returning echoes, they can locate and identify obstacles to their flight (vegetation, buildings) and capture small insect prey. Bats often fly and forage in groups. When other flying bats are present, they face the added challenge of separating out the echoes from their own broadcasts from the broadcasts and echoes created by these other bats, while still maintaining their flight path. To assess how bats address these challenges, we flew individual and then pairs of big brown bats (Eptesicus fuscus) through a curved flight corridor bounded by rows of closely spaced vertical hanging plastic chains that produced echoes mimicking those produced by dense vegetation. When flying alone, each bat broadcasts sonar sounds containing frequencies from 100-25 kHz in a characteristic pattern of alternating long and short time intervals. These short time intervals allow fast reactions to immediate collision hazards, while the long intervals allow the bat to peer deep into its surroundings to plan its upcoming flight path. When two bats fly towards each other from opposite ends of the curved corridor, they maneuver to avoid colliding. There are three distinctive biosonar reactions tied to these maneuvers. First, both bats increase the strength of their broadcasts (Lombard effect) during the brief time they are in close proximity. Second, they produce more short time intervals, speeding up their broadcast rate. Third, at the point where they are in closest proximity and the need for each bat to avoid being interfered with by the other bat is most acute, one of them sharply decreases the low-frequency end of its broadcasts to about 15 kHz. This unusual, asymmetric response allows this bat to distinguish echoes of its own broadcasts from those of the other bat, even though the total range of frequencies remains large. Bats place particular priority on the lowest frequencies in echoes, and having different lowest frequencies lets them separate out each other’s biosonar broadcasts and prevent mutual interference when close together.

Rivera-Parra, JL, jose.riverap@epn.edu.ec
De la Cruz, I.
Viscarra, S.
Vasconez, C.
Dueñas, A.
Xulvi, R.
Sorriso-Valvo, L.

Popular version of 5aABb2 – A tale of two singers: how do bats and bird mixed-flocks respond to petroleum industry noise in the Ecuadorian Amazon
Presented Friday morning, December 3, 2021
181st ASA Meeting, Seattle, WA
Click here to read the abstract

Industrial noise can have a significant impact on animal groups that rely on acoustic communication for fundamental survival activities. Our research focuses on two of these groups: insectivorous bats, which use ultrasound to navigate and find food; and mixed flocks of insectivorous birds, that rely on vocalizations to communicate about foraging direction and potential threats. The Yasuni Bio-sphere Reserve in the Ecuadorian Amazon is one of the most biodiverse spots in the world, but it is also a place with thriving oil exploitation activities.

It is well known that some disturbance, such as roads, or industrial noise, can be related to biodiversity loss, however, how much of these effects can be attributable to the noise caused by the oil exploitation have never been measured, nor has it been characterized. Furthermore, characterization of noise is usually done only in the audible spectrum, meaning the frequencies that us as hu-mans can hear, but is not done taking into account ultrasound.

To characterize the noise caused by oil exploitation we selected three different places, based on the potential source related to the oil industry, plus a control point: 1) drilling site, 2) processing facilities, 3) a control site, a forest with no disturbance. For all three sites recordings of both audible and ultrasonic sound were made in a transect from the border of the source of industrial noise to-wards the forest. To further analyze the effects of the noise, biological surveys were made both in birds and bats. We characterized bats and birds vocalizations, and the industrial noise profile, both in ultrasound and audible frequencies.

Our results suggest, in both groups, the immediate response is avoidance; this results, in the short and long term, in a biodiversity loss. These effects are proportional to how much noise the habitat itself absorbs, the complexity of the habitat, the complexity of the noise, and the distance from the source. In the long term the effects seem to include a change on habitat use, and modification on community composition. Thus is possible it can cause a disruption of ecosystem services by bats and birds, such as natural pest control, polinization, and seed dispersal, which can lead to a broader change in forest dynamic.

JoAnn McGee – mcgeej@umn.edu
VA Loma Linda Healthcare System, Loma Linda, CA 92357
Center for Applied and Translational Sensory Science,
University of Minnesota,
Minneapolis, MN 55455

Peggy B. Nelson – nelso477@umn.edu
Department of Speech-Language-Hearing Sciences and the Center for Applied and Translational Sensory Science,
University of Minnesota,
Minneapolis, MN 55455

Julia B. Ponder – ponde003@umn.edu
The Raptor Center,
College of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108

Christopher Feist – feist020@umn.edu
Christopher Milliren – milli079@umn.edu
St. Anthony Falls Laboratory,
University of Minnesota,
Minneapolis, MN 55414

Edward J. Walsh – ewalsh@umn.edu
VA Loma Linda Healthcare System,
Loma Linda, CA 92357
Center for Applied and Translational Sensory Science,
University of Minnesota,
Minneapolis, MN 55455

Popular version of 1pABb6 – A study of the vocal behavior of adult bald eagles during breeding and chick-rearing
Presented at the 181st ASA Meeting in Seattle, Washington
Click here to read the abstract

One of the many challenges associated with efforts to characterize the acoustic properties of free-ranging bald eagle (Haliaeetus leucocephalus) vocalizations in a behavioral context is the relative inaccessibility of individual, interacting signalers. Here, we take advantage of the opportunity to eavesdrop on vocal exchanges between a breeding pair inhabiting a nest furnished with a webcam and microphone located in Decorah, Iowa and managed by the Raptor Resource Project (www.raptorresource.org).

In a previous study centered on captive bald eagles at the University of Minnesota Raptor Center, five call categories, including so-called grunts, screams, squeals, chirps and cackles, were identified. The primary goal of this study was to extend the investigation into the field to begin efforts to characterize and compare the acoustic properties of calls produced in captivity and in the wild.

Predictably, many of the acoustic features of calls produced in captivity and in the wild are generously shared. However, preliminary findings suggest that at least a subset of calls exchanged by breeding pairs may take on a hybrid character, exhibiting blended variations of the chirps, squeals and screams characterized previously in captive birds. Calls analyzed here were taken from a variety of settings that include mating, exchanges associated with feeding at the nest, vocal reaction to intruders near the nest, and short distance call exchanges that appear to function as hailing signals.

The source of raw materials used to relate the behavior of the interacting pair to their vocal exchanges can be appreciated by observing the following audiovisual recording examples.

VIDEO 1
In this video, the female of the pair, an eagle known affectionately as Mom, is not so patiently awaiting the arrival of her partner, known by the less endearing name DM2. As DM2 arrives at the nest with a meal, Mom produces a call sounding a lot like the call of a sea gull; a call with the characteristics of a lower frequency version of the scream observed in captive eagles.

VIDEO 2
Here, Mom appears to be calling out to DM2 for a break from nesting. DM2 arrived shortly after the footage shown here and Mom takes off for higher ground. The call appears to be a commonly produced, seemingly multipurpose utterance closely resembling a spectrally complex version of a call observed in captive eagles known as the chirp.

VIDEO 3
In this sequence, Mom appears to summon DM2 in response to what appears to be an intruder, possibly another bald eagle, in the airspace surrounding their nest. Again, a complex variation of the chirp observed in captive eagles appears to serve as a territorial marker.

The take-home message of preliminary findings reported here is that the acoustic structure of at least a subset of calls produced by free-ranging bald eagles appears to be more nuanced and complex than those representing their captive counterparts. Elements typically representative of three primary call types in captive birds, namely chirps, screams and squeals, intermix in calls produced by free-ranging eagles, creating a vocal repertoire with subtle, but potentially meaningful structural variation. If differences reported here remain stable across a larger sample size, these findings will serve to underline the relative importance of our work in the field.