Impact of live trapping on stress profiles of Richardson's ground squirrel (Spermophilus richardsonii).

Researching the physiological ecology of natural populations requires an understanding of the impact of capture-induced stress because of its numerous effects on physiological processes. In many cases, initial blood samples to which comparisons are made are obtained well after capture and may differ markedly from free-ranging conditions. We examined the extent to which stress profiles of male Richardson's ground squirrels (Spermophilus richardsonii) were affected by short-term responses to live trapping. We compared stress profiles of true base animals (blood samples obtained <3 min of capture) with those of nominal base animals (blood samples obtained >1 h after capture). Total cortisol increased almost 40% whereas our measure of corticosteroid binding globulin (CBG) decreased by 21%, resulting in a two-fold increase in free cortisol levels in nominal base animals compared with true base animals. Capture caused androgen concentrations to fall to almost half of those of true base animals. Energy mobilization increased markedly (22% in glucose and 221% in free fatty acids). Although white blood cell counts did not change, the number of neutrophils was 48% higher in true base animals. There were no changes in hematocrit or lymphocyte counts. Although most of the changes were predictable, the changes in CBG and androgens were unexpected based on previous work on closely related Arctic ground squirrels (Spermophilus parryii). Our results emphasize the value of obtaining true base measurements whenever possible in order to assess the directions and degree of bias introduced by trapping.