Food availability affects behavior but not circulating gonadal hormones inmaternal Belding's ground squirrels

We tested predictions of hypotheses suggesting that the steroid hormones, t estosterone (T), progesterone (P), and estradiol(E-2), contribute to the en ergetic regulation of behaviors associated with rearing young in free-livin g female Belding's ground squirrels (Spermophilus beldingi). We provisioned some female S. beldingi with food rich in fat and calories, and used unpro visioned females as controls. We observed the behavior of females throughou t the reproductive cycle, and regularly collected blood samples to measure plasma hormone concentrations. Circulating concentrations of T, P, and E-2 were similar in provisioned and unprovisioned females, as were temporal pat terns of variation in these hormones. Peaks in rates of nest maintenance an d aggressive behavior occurred during gestation and were associated with el evated concentrations of circulating T, P, and E-2, raising the possibility that one or more of these hormones mediates behaviors that help females es tablish maternal nest sites and territories after mating. Temporal patterns of variation in behavior were similar among provisioned and unprovisioned females; however, rates of resting, vigilance, and aggression were higher a mong provisioned females, whereas unprovisioned females devoted significant ly more time to feeding and locomotion. Thus, our data suggest that in mate rnal S. beldingi, gonadal steroids play a role in mediating behavior associ ated with raising offspring, but do not facilitate changes in rates of beha vior associated with increased energy availability. (C) 2000 Elsevier Scien ce Inc. All rights reserved.