DETERMINANTS OF CHORUS PARTICIPATION AND THE EFFECTS OF SIZE, WEIGHT AND COMPETITION ON ADVERTISEMENT CALLING IN THE TUNGARA FROG, PHYSALAEMUS-PUSTULOSUS (LEPTODACTYLIDAE)

The individual mating success of male tungara frogs is best predicted by the number of nights spent in chorus activity, yet individuals are often absent from the chorus for several nights without calling at another site. To test whether males leave the chorus to forage to pay the energy cost of calling, males were captured in groups of four and their calls were recorded over 3 or 5 nights, while half of them were starved and the others fed. Feeding had no effect on the number of males that stopped calling, or on the changes in call rate, call complexity (number of secondary notes) and chorus leading over time. When they were released, fed males did not return faster to the chorus, and were not more likely to return, than starved males. Playback of a tape of a large chorus increased the number of males present in the small natural chorus. Chorus size in three pools was positively correlated with the minimum temperature, and negatively correlated with the rainfall, over the previous 2 days. These results suggest that males are conservative in their chorusing activity because chorusing increases predation risk, not because they need to forage. Males use variation in chorus size, rainfall or temperature to select those nights that offer reduced predation risk and increased mating opportunities. Playback of a tape of a large chorus caused males in a small chorus to increase their call rate by 104%, their call complexity by 38%, and the net energy cost of calling by 70%. Male size and weight had no effect on the mean call rate, call complexity or the amount of chorus leading, but were positively correlated with the maximum call rate of male; this effect may contribute to the higher mating success of larger males observed previously. Size and weight had no effect on the maximum rate of production of secondary notes, or on the influence of playback on call rate. Weight was correlated with the relative increase in call complexity as a result of playback; larger males use relatively more secondary notes in larger choruses, whereas smaller males use relatively more in small choruses. © 1990.