The cause of correlations between nightly numbers of male and female barking treefrogs (Hyla gratiosa) attending choruses

Abstract

The number of males displaying in a lek or chorus each day is often positively correlated with the number of females visiting or mating in the aggregation. I tested hypotheses that might explain such correlations in a study of the barking treefrog (Hyla gratiosa). Experimental reduction of the number of calling males did not reduce female visitation, ruling out the hypothesis that such correlations are owing to female preference for, or passive attraction to, larger choruses. Separate regression of the numbers of males and females on 13 environmental variables explained 45--74% of the variance in the nightly numbers of males and females. Partial regression coefficients for most of the 13 variables were not significantly different between the sexes, and the relative importance of variables in explaining variation in the numbers of individuals was similar for both sexes. These results support the hypothesis that positive correlations between nightly numbers of males and females are owing to a similar response by both sexes to the same environmental variables. Thus, it appears that the intense sounds emanating from choruses of H. gratiosa do not function in long-range communication and may instead be an epiphenomenon of intense, short-range vocal competition for females. Copyright 2003.