Sample Abstracts

J. A. French, K. T. Phillips, and B. J. Proskocil
Nebraska Behavioral Biology Group and Psychology Department, University of Nebraska at Omaha, Omaha NE 68182-0274.
While a good deal is known about changes in gonadal hormone production throughout development and its modification by social factors in callitrichid primates, less is known about maturational changes in adrenal steroid hormone production. We present data on profiles of glucocorticoids in male marmosets to address this shortcoming. Urine samples were collected noninvasively from males residing in their natal family groups (n = 24) at ages varying from 1.2 to 35 months. For reference purposes we also measured urinary cortisol concentrations in a sample of breeding adult male marmosets. A cross-sectional sampling strategy was utilized, so not all males contributed samples at all age-points. Urinary free cortisol was measured via EIA. Levels of cortisol were higher in young infants (less than 3 months of age; > 40 mg Cortisol/mg Cr) than in any other age class, including adult males. After 3 months of age, levels drop to low concentrations (~ 10 - 15 mg/mg Cr) and remain low thereafter. While urinary testosterone peaks in sons at 12 months of age, there were no corresponding changes in cortisol excretion. Compared to sons in family groups, breeding adult males had significantly higher concentrations of urinary cortisol. As is the case in daughters, then, reduced gonadal function in sons is not associated with elevated cortisol, and must be mediated by mechanisms other than the HPA axis. Supported by NSF (IBN 97-23842).
P.T. Mehlman and D. Doran
Department of Anthropology, Stony Brook SUNY, Stony Brook, NY 11794.

Observations of 432 nighttime group nest sites (3309 individual nests) were made between 1995-1998 in a 502km site in the Dzanga-Ndoki National Park, CAR. With the aid of Ba'Aka trackers, fresh nest sites (<2 days) were located while tracking groups leaving trail in the rainforest. Nests were classified as adult silverback male versus all others (adult females, blackbacks, juveniles) on the basis of dung size and absence/presence of silverback hairs. Infant dung was not reliably found in all nest sites that included known infants, but was scored when found near mothers' nests (approximately 10% of sites). For nest sites in which number of silverbacks and nonsilverbacks could be identified (317), mean number of silverbacks nests per site was 1.2+0.4; 81% of these group sites contained only one silverback (n=256) and 19% contained two silverback nests (61). Mean minimum number of nonsilverback nests per group site was between 5.6+3.3 (minimum) and 6.5+3.5 (maximum). Minimum number of total nests per site (with dung near each nest) was 6.8+3.4. Maximum number of nests (with and without dung) was 7.7+3.6. Nest site counts ranged in size between 2 and 20 weaned individuals (single male nests excluded). These results indicate mean group size in this lowland gorilla population is 7-8 weaned individuals. Supported by National Science Foundation (SBR-9422438) and SUNY, Stony Brook.