The novel's main character states that a species of wild dog had lived on the island for her entire life without threatening its human inhabitants. This changed after another breed of dog was introduced by Aleutian invaders, who also killed most of the island villagers. She describes this new breed as larger, with yellow eyes and thick fur. This dog may have been a type of Alaskan malamute or Siberian husky.
Excavations conducted in 2008 by researchers from California State University's Department of Anthropology revealed evidence of dog burials on San Nicolas Island, the setting of the novel. The dogs had been buried approximately 800 years ago and were likely a crossbreed of Plains-Indian and Short-Nosed Indian dogs. This breed may be the one Karana refers to in the novel as "wild dogs."
The only dog that is named in the novel is given the name Rontu by Karana, who takes pity on it after she kills the rest of its pack. She speculates that Rontu was one of the Aleutian dogs whose interbreeding with the native wild dogs had led to increased aggressiveness against humans. Rontu is described as having gray fur and yellow eyes.
Karana undertakes an effort to eliminate the new crossbreed of native and Aleutian dogs after one of them attacks and kills her brother. She describes them as dwelling in caves and surviving by hunting animals, such as foxes. During her expedition, she comes across a litter of black pups and fends off an attack from a female dog.