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

Katie McHugh calls data from the observation tower of "Nai'a" to interns Mackenzie Consoer and Laura Bagge while intern Christina Toms photographs the dolphins in the group.

      The juvenile life stage is a fragile and formative time for young animals first learning to navigate complex social and ecological environments once independent of their mothers.  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 factors influencing survivorship of independent juveniles. Because of SDRP’s long-term research on the bottlenose dolphin communities in the area, the “natural laboratory” of Sarasota Bay provides a unique opportunity to address these issues.
      To this end, the main objectives of my dissertation project are: 1) to develop a better understanding of social and behavioral development of juvenile bottlenose dolphins and 2) to determine the major behavioral and ecological 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, which will allow for both a longitudinal and cross-sectional perspective on juvenile behavior.

      Preliminary fieldwork on this project began in summer 2005 and continued in summer 2006, both of which were at least partially affected by red tide.  In 2007, I spent the bulk of my time in the field, completing both winter and summer field seasons of behavioral observations.  So far, I have collected over 375 hours of focal animal behavioral follow data on 27 individuals (14 females:13 males) ranging in age from 3 to 12 years old.  While a few of these animals have died, gone missing, or had calves of their own since we first started the project, most are still frequently seen in Sarasota Bay, and I will finish observing the remaining focal juveniles in 2008.
      One of the main areas I’ve explored so far has been the effects of red tide on juvenile dolphin behavior.  While not originally intended to be a focus of this study, the first two field seasons coincidentally took place during periods when red tide was a factor.  Preliminary analysis has shown that both social behavior and activity budgets differ substantially during red tide.  Juveniles associated in larger groups and with significantly more community members, and spent less time foraging and more time socializing during red tide events, potentially as a consequence of underlying changes in relative prey availability and distribution (see article in Ecology section). 

Behavioral obeservation research vessel "Nai'a" moves on to another group of dolphins after completing focal animal behavioral observations.

      Additionally, I’ve spent time this year working with long-term SDRP data to examine the transition to independence for dolphin calves, calculating ages of separation and exploring life history, body condition, and social factors influencing the timing of independence for calves born into the Sarasota community since 1980. I am now beginning to investigate sex and seasonal differences in juvenile behavior (primarily association patterns, habitat use, ranging patterns, and activity budgets) and will start analyzing age-related changes in behavior and exploring factors influencing survival to adulthood in the coming months. 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 the Chicago Zoological Society, NOAA’s Fisheries Service, the UC Davis Graduate Scholars Fellowship in Animal Behavior, the Animal Behavior Society’s Cetacean Behavior and Conservation Award, and an NSF Graduate Research Fellowship.