Individual variation in response to simulated territorial challenge among territory‐holding song sparrows

Abstract

Lack (1946) suggested that male songbirds exhibit consistent individual differences in the vigor or manner in which they defend their territories against intrusion. The causes and consequences of such individual variation have not been incorporated into models of territoriality, however, because of a lack of experimental data confirming Lack's suggestion. In this paper, we test the possibility that male song sparrows Melospiza melodia who are successful territory holders differ consistently in the vigor with which they defend their territory, by conducting repeated song playback trials with the same set of territory‐holding subjects across a breeding season. We found only relatively weak seasonal trends in responsiveness: the amount birds sang in response to playback increased significantly across the breeding season and responsiveness was generally lower when a male's social mate was egg laying. By contrast, we found extensive variation among males in how closely they approached a simulated territorial intrusion. These individual differences remained significantly consistent across four rounds of playback trials that spanned the breeding season as determined by Kendall's coefficient of concordance. Our results confirm that some individual song sparrows are consistently more vigorous than others in territory defense, at least in one conspicuous aspect of their behavior, and suggest that further work is needed to understand the nature and consequences of variation in patterns of defense among successful territory holders.

Does a rival’s song elicit territorial defense in a tropical songbird, the Pied Bush Chat (Saxicola caprata)?

“…In other words, if male song increases primarily as a result of territorial defense, then seasonal song activity should be positively correlated with the territorial intrusions and escalated aggressions (Chiver et al, 2015). Such results have been reported in Song sparrows (Hyman, Hughes, Searcy, & Nowicki, 2004;Nowicki, Searcy, Krueger, & Hughes, 2002).…”

Agonistic urban birds: elevated territorial aggression of urban song sparrows is individually consistent within a breeding period

“…It is unclear, however, whether the elevated territoriality of urban birds is a consistent habitat-related behavioural difference. Territorial aggression is individually repeatable in rural male song sparrows [9,10], but it is unknown whether this behaviour is individually repeatable when simultaneously considering both urban and rural birds. To address this, we tested whether the territorial aggression of urban and rural song sparrows is individually consistent and repeatable within a breeding period.…”

Individual differences affect honest signalling in a songbird

“…As mentioned above, previous research in our study species and others [28,29] has established that personality differences in aggressiveness is an individually consistent trait that is correlated with boldness [9,10] or exploration [6,8], and thus constitutes a behavioural syndrome or a personality trait. Although aggressiveness is a well-studied personality trait and potentially drives expression of both aggressive behaviours and aggressive signalling by itself, it would not be sufficient to explain partial reliability of signalling.…”