Age Determination, Life History and Juvenile Behavior in Bottlenose Dolphins (Tursiops sp.) in Shark Bay, Australia
Krzyszczyk, Ewa Beata
Although of theoretical interest, the juvenile period in mammals is a relatively neglected area of research. In large-brained and social mammals, such as bottlenose dolphins, where juvenile periods are prolonged, life history theorists assume they must need or use this period to solve specific adaptive problems, such as growth, skill development or social bond formation. Here, I examine the period of immaturity in bottlenose dolphins with a diverse set of approaches: physiological and hormonal development, age- and sex-specific survival, and juvenile behavior and relationships. The 30-year Shark Bay dataset provides a unique opportunity to investigate these features longitudinally.Chapter 1 investigates the ontogeny and possible functions of ventral speckling in bottlenose dolphins in Shark Bay. Speckles first appear at 10 yrs of age around the genital area, just prior to the typical age of first pregnancy. Throughout a dolphins' lifespan, speckles increase in number and density. The most promising functional explanation is that speckles offer cues to reproductive maturity, social status (age) or condition.Chapter 2 investigates age and sex-specific survival rates. 1st yr calves had significantly lower survival rates than older calves or juveniles. Adult survival was highest, with no significant difference between the sexes, possibly because bottlenose dolphins in Shark Bay are sexually monomorphic where males compete intensively for mates.In Chapter 3, I focus on the causes of mortality associated with ingestion of large amounts of seagrass. Since seagrass impaction was most common in young calves compared with older dolphins, maternal loss by either separation or death was considered to be the main cause. The pattern underscores the importance of the calf period for developing hunting skills and helps explain why bottlenose dolphin calves have some of the longest periods of dependence documented to date.In Chapter 4, I concentrate on behavioral and social development during the transition to independence, two years pre- and two years post-weaning. Juvenile activity and social patterns illustrate the specific ecological and social challenges they face in relation to adulthood.Finally, Chapter 5 examines the methodology for assessing hormones in blow (exhaled breath condensate) including cost effective extraction and analytical techniques.
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