Edmund Gerstein – email@example.com
Charles E. Schmidt College of Science
Department of Psychology
777 Glades Road
Florida Atlantic University
Boca Raton, Florida 33486
University of the Aegean
Lesvos Island, Greece
Florida Atlantic University / Harbor Branch Oceanographic Institute
Fort Pierce, FL 34946
Florida Marine Resources Council
Stuart, FL 32905
Edgerton Research Laboratory
New England Aquarium, Boston, MA 02110
Popular version of paper 4pAB13 presented at the 2014 167th ASA Meeting in Providence, RI.
Sound File 1. Typical gunshot sound recorded from a male in a surface active group in the southeast critical habitat (note the 191[infopopup tag=dBdefinition] peak amplitude)
Figure 1. Mother and calf
Figure 2. Mother just before gunshot near recording buoy
Of 32 different isolated mother-calf pairs, gunshots were recorded from six identified females of varied ages and maternal experience. Most of the gunshots were emitted by mothers when their young (1-6 week old) calves separated from them during the calves’ curious (exploratory) approaches toward objects on the surface. The social and behavioral context of female gunshots suggest these calls were associated with maternal alarm and or communication directed toward their calves. However, they were not overtly effective as call back signals (during our observations) as the calves continued unabated on their forward paths of exploration.
The spectral and temporal characteristics of these female gunshots resemble those attributed to adult males in the Bay of Fundy (Parks et.al., 2005) and those recorded from surface active groups in the southeast critical calving habitat (Trygonis et.al., 2013). However, the (female) gunshot calls are orders of magnitude quieter (-30dB). (Figures 3, 4, & 5).
While a specific articulation site or mechanism for gunshot production is unknown, the ability to vary intensity of impulsive sounds lends support to Parks et al (2005) who suggested there is a unique anatomical trait within balaenid whale species which enabled the internal production of these impulsive gunshot sounds. The significantly lower intensity “quiet gunshots” emitted by the mothers posed minimal risk of injury to nearby calves and also resulted in relatively small detection ranges, both of which would be beneficial for mothers trying to protect their calves. Daylight observations and acoustic recording in the southeast critical calving habitat indicate that each mother and calf pair functioned as “isolated social dyads or islands” and actively avoided other whales. The mothers and calves are predominantly silent during the first six weeks of development, and exhibit only low intensity social calls as calves mature. Isolation, quiet gunshots, and the whales’ overall acoustic quiescence may function in predator avoidance and serve to minimize acoustic detection or harassment by adult males, juveniles and other conspecifics in the area.
The social and behavioral context of these gunshot calls naturally precludes any reproductive function or specific communication signaling by the female toward any individuals other than her calf. Synchronized underwater acoustic and surface video recording presented below chronicled gunshots and behavior as a mother interacted with a surface buoy in the forward path of her and the calf (Video file 1).
Video file 1. Mother approaches recording buoy, note how she does not avoid the buoy, but actively pushes it with her head and clears a path for her calf to follow. The event is accompanied with two gunshots as she interacts with the gear.
The behavior exhibited during this chance encounter offers an insight into how and when a whale (mother in this case) might interact with surface gear (fishing floats, as well as buoys), and suggests that gunshots may also be emotive indicators of heightened stress and agitation caused by anthropogenic factors, as well as naturally occurring social behavior.
Parks, S. E., Hamilton, P. K., Kraus, S. D., and Tyack, P. L. (2005). “The gunshot sound produced by male North Atlantic right whales (Eubalaena glacialis) and its potential function in reproductive advertisement,” Mar. Mamm. Sci. 21, 458–475.
Trygonis V., Gerstein E.. Moir, J., & McCulloch, S. (2013). “Vocalization characteristics of North Atlantic right whale surface active groups in the calving habitat, southeastern United States,” J.Acoust. Soc. Am. 134, 4513-4531.