Male territoriality, fighting and assessment of fighting ability in the Australian frog Uperoleia rugosa

Abstract

Males of Uperoleia rugosa form aggregations around the breeding pond. Within the aggregations, each calling male maintains an exclusive zone in which it does not tolerate another calling male. However, attacks on silent intruders, satellite males or females were never observed. Territorial males warned calling intruders by changing from advertisement calls to encounter calls (a display); if the intruder persisted in calling the resident would either attack or retreat and call elsewhere. Fights were usually won by the heavier males, and males of similar weight were more likely to fight, whereas males retreated from opponents that were substantially heavier. Calling was energetically costly and territorial males lost weight and thus their fighting abilities declined, whereas silent satellite males gained weight and were able to oust lighter territorial males. There was thus a dynamic interchange between territorial and satellite males depending on their relative weights. The playback of recorded advertisement calls showed that males can assess each others' fighting abilities on the basis of their vocalizations. Males retreated from a loudspeaker broadcasting the calls of a larger male but they attacked the loudspeaker if the calls of smaller or similar sized males were played ( N=39, P<0·001, one-tailed binomial test). Dominant frequency was probably the call parameter used in assessment as it was correlated with the weight ( r=−0·71, P<0·001, N=100) and hence the fighting ability of the caller, but this hypothesis needs further testing.