Juvenile dolphin behavioral development and survival strageies
By Katherine McHugh, PhD Candidate, University of California, Davis

F170 engaged in social play with other juveniles, August 2006.

The juvenile life stage is an extremely vulnerable and formative time for developing marine mammals, who must learn to find food and avoid predators in a complex underwater environment while forging social relationships and practicing skills critical for survival. While bottlenose dolphins are among the best studied cetaceans, virtually no work has focused on understanding behavioral development between weaning and sexual maturity or determining the selection pressures acting on the juvenile life stage. Many factors remain poorly understood—for example, what are the major differences between the behavior of juvenile and adult animals? How do skills and relationships critical for adult survival and reproductive success develop through the juvenile period? What social, ecological, and behavioral factors influence survivorship of juvenile dolphins? Because of SDRP's long-term work on the bottlenose dolphin communities in the area, the "natural laboratory" of Sarasota Bay provides a unique opportunity to address such questions.

To this end, the main objectives of my dissertation project are: 1) to develop a better understanding of the range of variability in social and behavioral development of bottlenose dolphins and 2) to determine the major ecological and behavioral influences on survival of free-ranging juvenile dolphins. I am investigating these questions by combining long-term sighting and mortality data from the resident dolphin community in Sarasota Bay with new information collected via boat-based surveys and focal animal observations on individually-identifiable juveniles. Preliminary fieldwork on this project began in 2005 and continued in Summer 2006. So far, I have collected over 160 hours of focal follow behavioral data on 26 individuals (13 females and 13 males) in the Sarasota community ranging in age from 2 to 11 years old. I plan to continue observing these juveniles over the next two years, which will allow for both a longitudinal and cross-sectional perspective on the social and behavioral development of juvenile dolphins in Sarasota Bay and provide a more detailed understanding of the maturational challenges facing newly independent juveniles on their 'path to adulthood.'

I am currently finishing data entry from our 2006 season and working on preliminary analysis of both long-term and focal follow data. I will be examining how dolphin association patterns, habitat use, ranging patterns, and activity budgets change from weaning to sexual maturity, investigating both between and within-sex differences in developmental trajectories as well as ways in which behavior patterns differ from adults. In addition, I will explore how juvenile dolphin behavior influences survival to adulthood by using long-term data to compare the ranging and association patterns of individuals who died before reproducing with those known to produce at least one offspring successfully. Finally, I hope to use this information to explore the potential social and ecological functions of mixed-sex juvenile groups by testing how group size and composition are influenced by factors such as activity state and habitat type, which may serve as proxies for predation risk and food availability. This portion of the project will benefit greatly from insights gained through SDRP's ongoing prey abundance and distribution research and may also incorporate some analysis of red tide effects on juvenile grouping behavior (since we have already noticed that there may be changes in juvenile behavior and group size during red tide events). This research will reveal the range of variability in developmental trajectories of bottlenose dolphins and provide missing data on how juvenile dolphin behavior patterns vary by sex, age, season, and time since weaning. Such information will provide a more comprehensive understanding of dolphin life history and survival strategies, which may have implications for conservation and management of long-lived coastal cetaceans.

Support for this project has come from NOAA Fisheries, the UC Davis Graduate Scholars Fellowship in Animal Behavior, the Animal Behavior Society's Cetacean Behavior and Conservation Award, and a NSF Graduate Research Fellowship.