Effect of brief exposure to a potential predator on cortisol concentrations in female Columbian ground squirrels (Spermophilus columbianus)

We examined the effect of exposure to a potential predator on cortisol conc entrations in captive female Columbian ground squirrels (Spermophilus colum bianus) and determined if lactation mitigated this cortisol response. Lacta ting and nonlactating females were exposed to a dog (Canis familiaris) for 5 min once a week over a 8-week period. Blood was collected 5 min and 2.5 a nd 4.5 h after exposure to the dog. Females exposed to the dog had higher c oncentrations of total (but not free) cortisol than unexposed females only in the 5-min blood sample. Over the active season, total- and free-cortisol levels were 37-47% higher in females exposed to the dog than in unexposed females in early to mid-July when young were being weaned. The cortisol res ponse to the dog was suppressed during lactation. Cortisol levels were, on average, 41-59% lower during lactation than during nonlactation 5 min (but not 2.5 or 4.5 h) after exposure to the dog.