Mating Behavior of Columbian Ground Squirrels
Type of DegreeDissertation
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Columbian ground squirrels (Spermophilus columbianus) are diurnal, herbivorous, colonial, and hibernatory rodents that reside in the Rocky Mountains of western North America. During April-July in 2005-2007, field assistants and I studied the mating behavior of Columbian ground squirrels at colony DOT in Sheep River Provincial Park, Alberta, Canada, by following a well-established protocol that consisted of various techniques that were applied in the following order of priority: (i) live-trapping of all individuals 1-2 days after emerging from hibernation in spring for weighing and sexual condition examinations, along with eartagging and painting a unique marker on the fur with black-dye for long-term identification; (ii) focal animal sampling for behavior and location of breeding females; (iii) all-occurrence sampling and digital recording of vocalizations emitted during courtship interactions of sexually mature males and females; (iv) all-occurrence sampling of amicable and hostile dyadic interactions involving all individuals; (v) scan sampling at 20-30 minute intervals for location and behavior of all individuals in view; (vi) all-occurrence sampling of predation events, predatory attacks, and predator sightings that involved the study animals as victims or targets. My intention in obtaining these data was to decipher the consequences of six different behaviors on which natural selection would act to favor expression of the traits leading to the behaviors. My approach was to generate as many options as possible for the environmental context of a behavior, and then to derive a priori expectations from those hypotheses that I could quantify in the field, either under natural conditions or experimentally. Columbian ground squirrels have a promiscuous mating system that exhibits a conflict of interest between males and females regarding the optimal number of mates per females. That is, territorial adult males become reproductively successful by monopolizing females, while females attempt to mate with multiple males. Thus, males and females have evolved auditory signals exchanged during mating interactions that are consistent with these interests. Males engaged in postcopulatory mate guarding, which included hostile encounters with other males after emerging from a copulatory burrow, violent herding of females to keep them close to the copulatory area as she attempted to court other males, and a repetitive cheeping vocalization which I deemed the ""mating call"". A postcopulatory ""estrus call"" emitted by females while they attempted to escape the guarding of their consort male appeared to assist females in finding additional mates during their estrus, as females that called were more likely to mate with another male than females that did not call.