By Katie McHugh, PhD, Chicago Zoological Society
The juvenile period can be fragile and formative for young animals learning to navigate complex social and ecological environments. My doctoral dissertation project used the long-term natural laboratory of Sarasota Bay to explore behavioral development of bottlenose dolphins, provide insights into the functional significance of juvenile groups, and examine the effects of environmental disturbance on the behavior of newly-independent animals. To achieve this, I combined long-term sighting records from Sarasota Bay with behavioral observations on 27 young resident dolphins during 2005-2008. This research is one of the first studies of independent juvenile behavior in cetaceans and provides a more comprehensive understanding of behavior throughout life history as well as behavioral responses to disturbance events. In 2010, this research officially came to a close with the completion of my dissertation through the Animal Behavior Graduate Group at UC Davis.
In general, I found substantial individual variation in the behavior patterns and developmental trajectories of young bottlenose dolphins. Sex- and age-related differences in juvenile behavior were evident, especially in social behavior, and many of these differences probably relate to the differing future social roles of males and females. Juvenile dolphins spent a relatively large amount of time devoted to social behavior and had a general tendency to engage in alloparental behavior. While juveniles interacted with a wide variety of individuals, young dolphins showed a distinct preference for interacting with other juveniles.
In addition, male and female dolphins in Sarasota Bay exhibited a high degree of attachment to the region where they were raised and had similar ranging and habitat selection patterns during the juvenile period. Juveniles displayed dramatic reductions in home range size after independence, whereby individuals used only a subset of their former range after separating from their mothers and then expanded their movements as they got older. Habitat preferences appear to be transmitted from mother to calf early in development, and there also appear to be lasting maternal influences on sociality and ranging patterns after independence.
Several facets of their behavior suggest that newly independent animals may actively seek social opportunities and that they likely face special challenges due to their smaller size and relative inexperience. Taken together, the behaviors exhibited by young dolphins point towards the probable importance of juvenile groups for promoting socialization and providing predator protection benefits.
Finally, I found that inshore dolphins displayed a suite of behavioral changes associated with severe red tide blooms, including significantly altered activity budgets, increased sociality, and expanded ranging behavior. This portion of my dissertation was recently published in Marine Mammal Science.
Support for this project came from the Chicago Zoological Society, NOAA Fisheries Service, the UC Davis Graduate Scholars Fellowship, the Animal Behavior Society’s Cetacean Behavior and Conservation Award, and an NSF Graduate Research Fellowship.