Shannon Gowans

Social structures and grouping behaviors of odontocetes are under strong evolutionary pressures, as they influence mating opportunities, calf survival, predation, and foraging efficiency. The fission-fusion nature of most odontocete groups facilitates fine-scale spatial and temporal variability and establishes relationship complexity at the core of odontocete social structure. Different communities of the same species vary in social structure, as do different individuals within the same community. The same individuals can also display different social structures in different conditions. Advances in field techniques and data analyses have improved our ability to tease out nuances of social structure. Future work is essential for understanding evolutionary bases of odontocete social grouping, to focus more on interactions as well as associations, incorporate long-range acoustic communication and multivariate analyses of social and ecological variables, and move to agent-based analysis, where each individual (or collection of individuals) can act autonomously and independently. Social structural plasticity is key to the success of odontocetes and may also play an important role in speciation.

This chapter describes the bottlenose or bottlenosed whales, large and robust beaked whales (6–9 m) distinguished by their large bulbous forehead and short dolphin-like beak. They are chocolate brown to yellow in color, being lighter on the flanks and belly. This coloration is believed to be caused by a thin diatom layer. Newborns are gray with dark eye patches and a light-colored forehead. The maxillary crests of males become larger and heavier with age, leading to a change in the shape of the forehead, with mature males having a flat, squared-off forehead whereas females/immature males have a smooth rounded forehead. The dense bone in the male's forehead may be used for male–male competition, as males head-butt one another. Males possess a single pair of conical teeth at the tip of the lower jaw (in females, they remain unerupted); however, these teeth are rarely visible in live animals. Northern (H. ampullatus) and southern (H. planifrons) bottlenose whales are the only recognized species within the genus Hyperoodon in the family Ziphiidae. Recent molecular work on southern bottlenose whales indicates that there may be more than one species. Sightings of a large beaked whale in the tropical Pacific has been identified in the past as a bottlenose whale (either H. planifrons or a third, undescribed Hyperoodon sp.); however, recent evidence suggests these whales are Longman's beaked whales (Indopacetus pacificus).