


Corresponding author.


Most of what we know about cetacean biology and ecology comes from studies of relatively common species. Despite their distribution throughout the tropics and sub-tropics, pygmy killer whales (Feresa attenuata) are rare throughout their range and are one of the most poorly-known species of odontocetes. During a 22-yr study of short-finned pilot whales (Globicephala macrorhynchus) off the island of Hawai‘i, we opportunistically photo-identified pygmy killer whales whenever encountered. As part of a directed multi-species study throughout the main Hawaiian Islands from 2000 through 2007, we also photo-identified individuals and obtained information on habitat use and behavior. This species was extremely uncommon (representing only 1.2% of odontocete sightings in directed efforts). Given the low encounter rates, assessing trends of this population cannot be feasibly done with line-transect surveys. Despite their rarity, 80% of the distinctive individuals within groups documented off the island of Hawai‘i were seen on multiple occasions, individuals were resighted over periods of up to 21 yr, and there was evidence of year-round use of the area. Association analyses indicate stable long-term associations in mixed-sex groups. High resighting rates indicate a small population of island-associated individuals that may be at risk from anthropogenic impacts.