Alarm calling, stress, and fitness in central versus peripheral territories of Richardson’s ground squirrels (Urocitellus richardsonii)

Abstract

Selfish herd theory predicts that as predators usually approach from the periphery of a group, survivorship and reproductive output of peripheral group members should be decreased. Non lethal encounters with predators may affect prey through the costs associated with increased activation of the hypothalamic pituitary-adrenal axis. Richardson’s ground squirrels (Urocitellus richardsonii) defend territories within their colonies and thus may experience differential fitness outcomes based on the location of their territory. I recorded U. richardsonii alarm vocalizations with Wildlife Acoustic SM3 audio recorders at centre and edge locations of a colony to estimate predation pressure and predator type (airborne vs. terrestrial), quantified faecal glucocorticoid metabolite (FGM) concentration as a measure of stress, and tracked offspring production and survivorship of females and their young for a year. The results obtained suggest that individuals occupying centre and edge areas experience different levels of predation pressure, but not FGM concentration, survival, or offspring production.