Territorial intrusions by pikas (Ochotona princeps) as a function of occupant activity

Pikas (Ochotona princeps) defend individual territories on talus. We tested the short-term stability of pika territories and found that although animals may intrude on the territories of conspecifics at any time, they were much more likely to do so if the occupant was inactive. Pikas usually waited until occupants were unavailable to defend their territory before intruding, apparently to avoid detection and repulsion by the occupant. Intruder avoidance of active occupants was most pronounced among same-sex dyads and non-nearest neighbours. Instances of territory intrusion were most frequent among nearest neighbour heterosexual dyads. Most cases of intrusion appeared to be related to eventual relocation of territories, deterring settlement of unfamiliar conspecifics on nearby vacant territories, and/or increasing familiarity with nearest neighbours of the opposite sex.