Patterns of pair boldness and mate recognition in song sparrows (Melospiza melodia)

Individual variation in behaviors such as aggression or boldness has the potential to influence the survival and reproductive success of individual animals. For example, individual variation in boldness means that some individuals will be more explorative and risk-tolerant than others, which could allow them to be more active in the face of danger or disturbance. Individual variation in boldness has been studied in many species, but fewer studies have examined patterns of boldness in mated pairs of animals. For many seabird species and some songbirds, mates tend to have similar levels of boldness and other personality characteristics. This suggests that coordination and decreased conflict between mated parents may allow for more effective care of young, leading to increased reproductive success. Boldness in male song sparrows (Melospiza melodia) has been shown to be both variable among individuals and repeatable for individuals, but similar work has not been conducted on females of the species. To determine if song sparrows within mated pairs have similar, different, or unrelated levels of boldness, we conducted Carolina wren (Thryothorus ludovicianus) alarm call playback experiments, simulating the presence of a predator, on the territories of 30 song sparrow pairs. At 24 of these territories, we conducted at least two playback trials to determine if boldness is repeatable for males and females. In a second study of the ability of song sparrow pairs to coordinate their boldness responses, we used playback experiments of song sparrow alarm calls to investigate whether males can distinguish between the calls of a stranger and their mate. Boldness and male response to a mate versus stranger were measured as the average distance from the playback speaker and the number of calls produced by each subject bird. Boldness, as measured by both distance from the speaker and number of calls, was repeatable for individuals and variable among individuals for males and females. Males and females produced a similar number of calls on average, although there was not a significant correlation between the number of calls produced by males and females within pairs. This suggests that the number of calls produced by one mate is unrelated to the number of calls produced by the other. Within a mated pair, males and females had similar levels of boldness as measured by average distance from the speaker. Song sparrows may mate assortatively for boldness or modify their behavior to match their mate’s. In response to alarm calls of a stranger versus a mate, male song sparrows got closer to the speaker in response to calls from a stranger, suggesting that males can recognize their mate’s alarm calls, which could allow for greater coordination when responding to threats on their territory