Hormonal and behavioral correlates of estrus in captive giant pandas (Ailuropoda melanoleuca)

This dissertation explored three hypotheses to explain differences in the rates of proceptivity, attractivity and receptivity during the mating season among captive giant panda females (Ailuropoda melanoleuca). The three hypotheses are: (1) Individual differences in ovarian hormones and (2) corticosteroids are associated with variation between females in rates of sexual behavior; and (3) male interactions play a role in modulating female sexual behavior. To test these hypotheses, ovarian and adrenal hormones were measured in urine, and focal animal observations were used to collect behavioral data from 12 captive females at the Wolong Breeding Center in China. These data were used to compare the behavior and hormones of cycling vs. non-cycling females and to investigate the role of hormones and social factors in determining the expression of proceptivity, attractivity and receptivity during the mating season.; The results demonstrated the importance of both hormonal and male behavior influences on the expression of estrous behavior in giant panda females. Both male and female behavior varied temporally with cycling females' hormone levels; peak rates of female sexual behavior and male approaches were associated with elevated estrogen levels. Only cycling females displayed receptive behavior. However, non-cycling females exhibited low rates of proceptivity and attractivity during the mating season. In comparisons among cycling females, there were no significant differences in either hormone levels or rates of sexual behavior between females grouped by either mating activity (during coordinated pairings) or fertility. Combined, these results suggest that there may be a hormone threshold for the exhibition of receptive behaviors. However, once that threshold level is reached, variation in estrogen levels does not predict variability in copulatory success or fertility in cycling females.; In regard to the role of adrenal hormones and reproductive behavior, corticosteroids were not predictive of behavioral differences between cycling or non-cycling females, or between groups of cycling females.; These results suggest that although ovarian hormones are necessary for the expression of receptive behaviors, variation in copulatory success and birth success among estrous females may be more closely linked to socio-sexual factors than to variation in ovarian and adrenal hormones.