In Kanyawara, the appearance of an estrous female chimpanzee often precipitates violent commotion. Large parties form with most of the community males present. Males follow the female closely, attempting to mate with her, and using aggression to discourage other males from doing so. The prize is fathering her next offspring. The costs of these activities to males have not previously been documented. In a new study by KCP researchers, Alexander Georgiev and colleagues investigated the foraging costs of male mating effort by observing males on days when no estrous females were available and when males competed for copulations with highly attractive females. Males, on average, spent about one hour less time feeding on days when they were competing for access to estrous females. This cost was only evident when the females were mothers, as they excite the most intense aggressive competition. Such a decrease in feeding time is likely to produce energetic shortfalls, implying that the ability of males to invest in mating effort depends on their condition. Surprisingly, high-ranking males, who in general are more aggressive and obtain more copulations, did not show greater reductions in feeding time than less-successful, low-ranking males. This may be the result of male chimpanzees maintaining strong and enduring bonds with each other, which sometimes necessitates high-ranking males tolerating the mating attempts of their allies. Such behavior might ameliorate the high costs of mating effort for the highest-ranking individuals, and result in similar costs accruing across the dominance hierarchy.