SEX-RATIO VARIATION IN THE YUMA BAT (MYOTIS-YUMANENSIS)

Sex allocation theory predicts that monomorphic species should produce natal sex ratios near unity. We measured natal sex ratios in a matern ity colony of approximately 1600 yuma bats (Myotis yumanensis) near Sq uilax, British Columbia, during June and July 1991. Overall, the natal sex ratio did not differ from unity but the sex ratio did vary signif icantly throughout the summer. Variation appears to be related to an i nteraction between maternal age and date of birth. This evidence sugge sts that facultative manipulation of the sex of the offspring by indiv idual females may occur within the population.