The juvenile period is important for young animals learning to navigate complex social and ecological environments once independent of their mothers. While bottlenose dolphins are well-studied, little work has focused on understanding behavioral development between the periods of weaning and sexual maturity, or determining factors influencing survivorship of independent juveniles. Because of the wealth of long-term research conducted by DRCI, the “natural laboratory” of Sarasota Bay has provided a unique opportunity to address these issues in my graduate research.
The main objectives of my dissertation project have been to develop a better understanding of social and behavioral development of juvenile bottlenose dolphins as well as to explore the major influences on survival of free-ranging juvenile dolphins. I have been investigating these questions over the past four years by combining long-term sighting and mortality data from the resident dolphin community in Sarasota Bay with new information collected via focal animal observations on individually-identifiable juveniles in the community, providing both a longitudinal and cross-sectional perspective on juvenile behavior.
Fieldwork for this project ran from 2005 through 2008, resulting in nearly 600 hours of focal follow behavioral data on 27 individuals (14 females and 13 males) in the Sarasota Bay community ranging in age from 2 to 13 years. While a few of these animals died, went missing, or matured and had calves of their own, most were observed in each of my six seasons, and it has been extremely interesting to watch their behavior and relationships change over time, especially as several males began forming alliances and some females got closer to becoming first-time mothers.
For the past year, I have been working on analyzing both long-term and focal follow data and writing up my results. One of the main areas I explored early on was the effect of red tide on juvenile dolphin behavior. While not originally intended to be a focus of this study, my first two field seasons coincidentally took place during periods when severe red tides occurred in Sarasota Bay. When I compared the behavior patterns of juveniles during red tide and non-disturbance periods, I found that sociality, activity budgets, and ranging patterns were substantially altered during red tides, potentially as a consequence of underlying changes in relative prey availability and distribution. This analysis is currently being written up for publication. Additionally, this year I have completed many of the major analyses for my dissertation, using focal follow data to explore individual variation and sex, seasonal, and age-related differences in juvenile behavior. [pullquote right] I’ve found that sex differences are already emerging in activity budgets and association patterns, with males showing a particular propensity for social interaction and exploration during the juvenile period. [/pullquote]For example, I’ve found that sex differences are already emerging in activity budgets and association patterns, with males showing a particular propensity for social interaction and exploration during the juvenile period. Also, seasonal differences are evident in most behavioral parameters, and sociality and ranging patterns change as juveniles mature. Finally, I’ve also drawn on long-term data to investigate factors influencing age at independence for dolphin calves, continued maternal influence on sociality and ranging patterns post-independence, as well as behavioral and ecological effects on juvenile dolphin survivorship. 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 provides 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 Fisheries, 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.