Cycles d’activité vocale chez les Amphibiens Anoures de la région de Yaoundé (Cameroun)

Abstract

Annual cycles of vocal activity in the Anuran Amphibians of the Yaoundé area (Cameroon). — The vocal activity of Anuran males was monthly or fortnightly recorded during periods of one to fifteen years in a number of localities of the Yaoundé area (Cameroon) between 1970 and 1993. Some 8 000 “ acoustic occurrences” were obtained, which allowed to draw histograms depicting the annual cycles of vocal activity of 63 species (71% of the 88 species of the area). From the histogram shape, eight types of cycles, grouped in three categories, can be distinguished. Continuous cycles are represented in forest and secondary growth species, bimodal cycles are the rule for savannah species but are well represented too in other ecological groups, whereas unimodal cycles are proper to several forest species. Relations between vocal and seasonal cycles revealed various situations. All savannah species, half of secondary growth species and some forest species are opportunistic : their annual cycles are synchronized with the two rainy seasons. On the opposite, for the other species, there is no obvious correlation with seasonal conditions. That is the case for continuously active species, but also for species which exhibit two activity maxima in climatically differing seasons. This study also showed that peaks of vocal activity (in bimodal cycles) or minima (in continuous cycles) are not separated by equal intervals of time, a fact difficult to explain. It is finally recalled that populations, but not individuals, are concerned by this study. Some research orientations are suggested to improve our knowledge of this still unexplored side of the Anuran biochronology.