Frequency and Correlation of Surface Observed Behaviors of the Bottlenose Dolphin (Tursiops truncatus) in Cape May, New Jersey.
Collection of opportunistic data during whale watching trips can offer a wide range of insights into cetacean behavior. In addition to spatial information and long term tracking of individuals through photographic methods, notable short-term behaviors of individuals are recorded during sightings (Hauser 2007). Feeding and mating are two essential behaviors often observed at the surface in the bottlenose dolphin (Tursiops truncatus). Breaching is a spectacular behavior which is easily recorded due to its dramatic nature. Observing the occurrence of these three behaviors may lend insight into how various behaviors are related as well as the data collection process.
Data collected during the 2014 field season was utilized in this work. Data was segregated according to trip times to avoid unnecessary variables associated with time of day. Unless otherwise noted, listings of behavior occurrence are the percentages of total particular behavior listings out of the total sightings for a particular time of day. For time ranges, AM indicates 10:00-12:00, PM 13:00-16:00, and SS 18:00-20:00. incomplete datasets were not included in this analysis .
Figure 1: percent occurrence of behaviors.
|TRIP||BREACH %||FEEDING %||MATING %|
Figure 2. Breach occurrence in relation to feeding
|TRIP||BREACHING OCCURRING DURING FEEDING %||FEEDING SIGHTINGS WITH BREACHING %|
Figure 1. demonstrates that the most commonly observed of the three selected behaviors is feeding, which was uniformly observed during roughly 58% of the trips regardless of time of day. Feeding therefore seems equally likely to occur during any of the three trip times. Breaching and mating, while somewhat less predictable, also demonstrate similar occurrence across time periods. Breaching decreases slightly from morning to evening, but it is debatable whether this indicates a legitimate trend. Altogether the data indicates surprising stability of behavior regardless of the time of day.
Figure 2. represents an attempt to correlate breach occurrence with feeding behavior. Column A demonstrates that out of the total number of breaches during a given time period, a large proportion were observed along with feeding behavior. An average of roughly 70% of the total breaching observations occurred during feeding behavior. Even during feeding, however, breaching is relatively uncommon. Column B demonstrates that the number of feeding observations which include breaching out of the total number of feeding observations. While higher than breaching percentage with all sightings pooled, the average occurrence of roughly 27% is still relatively low. Therefore, while breaching is most likely to occur during feeding behavior, it clearly does not occur of necessity, and appears to apply only to certain feeding circumstances. There is the possibility that other variables must be explored to further investigate this relationship.
Reasons for a potential correlation of breaching and feeding behavior relate to issues of communication and prey capture (Perrin 2008). Breaching may produce long ranging, low frequency sounds which provide information to individuals about pod movement and structure useful during feeding. It has been suggested that breaching may function as a signal to the approach and surrounding of prey items (Thomas 1990). In addition, it has been theorized that the underwater shock caused by breaching may disorient prey items in the same way as fluke slapping (Perrin 2008). Finally, some breaching may be a result of high speed prey capture; on at least one occasion a dolphin was observed breaching vertically through a bubble net in an attempt to seize fish concentrated at the surface (personal observation). The fact that breaching may apply to feeding in only certain social or behavioral contexts may explain its apparently infrequent or irregular occurrence.
Further development of this study would involve analysis of wind speed and breaching to assess whether breaching may be an attempt to communicate more easily at the surface during times when more sound interference is present due to wind.
Michael A. Denk, Intern at Cape May Whale Watch & Research Center
.Thomas, Jeanette A,. Kastelein , Ronald A Sensory Abilities of Cetaceans: Laboratory and Field Evidence Plenum Press 1990 pg 527
Perrin ,William F., Wursig, Bernd, Thewissen, J.G.M. “Hans” Encyclopedia of Marine Mammals Academic Press; 2nd edition (December 8, 2008) pgs. 6-8