Behavior and Ecology of Not-So-Social Odontocetes: Cuvier’s and Blainville’s Beaked Whales

Abstract

While beaked whales are the poorest-known family of cetaceans overall, the behavior and ecology of two species of beaked whales, Cuvier’s (Ziphius cavirostris) and Blainville’s (Mesoplodon densirostris), have been studied extensively for more than 15 years in multiple areas around the world. This research was largely initiated as a result of the susceptibility of both species to react to high-intensity navy sonars, sometimes resulting in the death of individuals. In this chapter long-term studies of both species in Hawai‘i are reviewed, informed by research on these species elsewhere. Both species have small populations that are resident to the island slopes, evidenced by a combination of long-term photo-identification and shorter-term satellite tag deployments. The two species coexist by partitioning their habitat in three dimensions, with Cuvier’s beaked whales being found in deeper water, and diving deeper, than Blainville’s beaked whales. Diving and acoustic behavior of the two species appears to be driven in part by predator avoidance. Both species echolocate only at depth, foraging deep in the water column during the day and at night, with less time spent near the surface during the day in between the deep foraging dives. Ascent rates are also slower than descent rates. All of these factors are likely ways of minimizing detection from near-surface visually or acoustically oriented predators such as large sharks and killer whales. There appears to be no strong selective pressure for grouping in these species. Both are often found alone and on average are found in very small groups (medians: Cuvier’s = 2; Blainville’s = 3). Groups that do form appear to function in part to avoid predators (for females with small calves) and allow for mating opportunities (for adult males seeking mates). Individuals of both species tend to have ephemeral social relations, although one pair of subadult Cuvier’s have been documented together over an 11-year period. Blainville’s beaked whale males exhibit female defense polygyny, while sperm competition may play a role in the mating system of Cuvier’s beaked whales. Studies of these species in multiple areas spanning the tropics to temperate waters in two different oceans are beginning to earn them an important place in our overall understanding of cetacean ethology and behavioral ecology.