Male contests in the scarlet rosefinch (Carpodacus erythrinus) in relation to asymmetries in resource holding power and pairing status

Summary Inter-male contests in relation to asymmetries in their pairing status and resource holding power were studied in a population of the Scarlet rosefinch. Since males in this species do not defend territories before nest building, and since most males have full adult plumage, possession of territory and age are unlikely to be used as cues in the settlement of contests. Rather, two other features are used, namely size and pairing status. In this study, contests between two unpaired males were usually short displacements, whereas 56% of contests between two paired males were escalated. In the first case, the smaller male withdrew in all contests, whereas in the second case there was an equal probability of withdrawal with regard to size. There was no relationship between size difference and the probability of escalation in the contests. Most of the fights between paired and unpaired males escalated, namely in 60% of the cases where the unpaired male was smaller and in 75% of the cases where he was larger. The unpaired male withdrew in 18 out of 23 contests, suggesting that pairing status is more important than size in determining the outcome of a contest. There was no variance in size differences between contestants in short and escalated contests. This study demonstrates that there is a high competition between males for females in this population.