Under laboratory conditions, female three-spined sticklebacks (Gasterosteus aculeatus L.) show a mating preference for intensely red-colored males. We verified this female choice in the field by observing a freshwater stickleback population in its natural habitat. During the egg collection phase, individual courting males were localized with the aid of a dummy of a ripe female, caught and photographed under standardized conditions, and released. After males had stopped collecting eggs, we counted the number of eggs in the nests. The more intense a male's red breeding coloration, the more eggs he received. Simultaneous female choice experiments in the laboratory suggested that ripe females of this population preferred redder males. Breeding activities of the males in the field were clustered and seem to be synchronized within clusters. At one of the breeding sites, more intense red males were in better physical condition, but this was not the case at another site. Although several synchronized breeding cycles were observed, the majority of males seem to complete only one breeding cycl
