Do Male Natterjack Toads Join Larger Breeding Choruses to Increase Mating Success?

Abstract

Male and female natterjack toads, Bufo calamita, exhibited a high degree of breeding synchronization. A polynomial or exponential regression indicated that the operational sex ratio (OSR) between nights increased with number of males in the overall population; hence, OSR varied temporally with chorus size. The comparison of three different groups of calling males within the breeding area, separated from each other and differing in male numbers, revealed similar OSRs between groups. Therefore, OSR did not vary spatially with chorus size. On average, males that attended larger groups obtained higher mating success in one season but not in another. Male movements between groups were directed toward larger groups, with higher OSRs and higher number of calling males, but males did not increase their mating probabilities by moving to another group. Female distribution among groups was correlated with the availability of oviposition sites, but they were not attracted differentially to large male groups or to groups with more callers.