Fluctuations in Intra-Pair Calling Across Breeding Phases in Northern Mockingbirds (Mimus Polyglottos)

Abstract

When in close proximity, mated mockingbirds (Mimus polyglottos) often exchange a broad band call. The call is also produced by lone males and females. I observed single hew production and intra-pair hew exchange across three breeding conditions: when adults were only feeding young, when the male was nest building with no young present, and when the male was nest building in the presence of young still being fed by the pair. Fewer calls of either type were produced during nest construction, and the relative frequency of each call pattern differed among breeding conditions. The percentage of pair interactions with hew exchange dropped while pairs were nest building, while the percentage of interactions accompanied by single hews increased during nest construction. Moreover, when only one member of the pair called (single hews), it was almost always the female. During nest building with young present, more pair interactions were accompanied by hew exchange than when pairs built in the absence of young, and in pairs nest building with young present, the number of hew exchanges per 60 min was positively correlated with brood size. Patterns of behavioural interaction between males and females also differed across the three breeding conditions. While feeding young, males approached females more than females approached males, and during nest building, males departed from females more than the reverse. Moreover, the responses of each sex were affected by breeding phase. Females departed first more while feeding than while nest building, and males approached first more while feeding than while nest building. More follows occurred during nest construction than during feeding, and females followed males somewhat more during nest building than during feeding. These data suggest that 1) hews directed within the pair reflect intra-pair aggression; 2) a drop in hew exchange may signal increased readiness to renest; 3) males may be ready to renest before females, who continue to call after males stop; and 4) readiness to renest may be affected by the presence of dependent young.