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Abstract Seasonal plasticity in aggression is likely to be shaped by the contexts in which aggression is beneficial, as well as the constraints inherent in its underlying mechanisms. In males, seasonal plasticity in testosterone (T) secretion is thought to underlie seasonal plasticity in conspecific aggression, but it is less clear how and why female aggression may vary across different breeding stages. Here, we integrate functional and mechanistic perspectives to begin to explore seasonal patterns of conspecific aggression in female tree swallows (Tachycineta bicolor), a songbird with intense female–female competition and T‐mediated aggression. Female tree swallows elevate T levels during early breeding stages, coinciding with competition for nest boxes, after which time T levels are roughly halved. However, females need to defend ownership of their nesting territory throughout the breeding season, suggesting it may be adaptive to maintain aggressive capabilities, despite low T levels. We performed simulated territorial intrusions using 3D‐printed decoys of female tree swallows to determine how their aggressive response to a simulated intrusion changes across the breeding season. First, we found that 3D‐printed decoys produce data comparable to stage‐matched studies using live decoys, providing researchers with a new, more economical method of decoy construction. Further, female aggressiveness remained relatively high through incubation, a period of time when T levels are quite low, suggesting that other mechanisms may regulate conspecific female aggression during parental periods. By showing that seasonal patterns of female aggression do not mirror the established patterns of T levels in this highly competitive bird, our findings provide a unique glimpse into how behavioural mechanisms and functions may interact across breeding stages to regulate plasticity.
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Destruction of a conspecific nest by a female Superb Lyrebird: evidence for reproductive suppression in a bird with female-only parental care
Abstract Reproductive suppression, whereby individuals decrease the reproductive output of conspecific rivals, is well-studied in mammals, but while it is suspected to be widespread in birds, evidence of this phenomenon remains rare in this class. Here we provide compelling evidence of reproductive suppression in the Superb Lyrebird ( Menura novaehollandie ), with the first audio-visual documentation of the destruction of one female’s nest by another. We propose that nest destruction may be a strategy that females use in protracted territorial negotiations spanning multiple breeding seasons, and discuss how reproductive suppression could explain puzzling nesting behaviours in this species, such as the construction of multiple unfinished nests in each breeding season. More broadly, these results reveal high intra-sexual competition among female lyrebirds, and thus may provide an explanation for their elaborate vocal displays.
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- Award ID(s):
- 1755132
- PAR ID:
- 10186229
- Date Published:
- Journal Name:
- Behaviour
- Volume:
- 156
- Issue:
- 15
- ISSN:
- 1568-539X
- Page Range / eLocation ID:
- 1459 to 1469
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1163/1568539X-00003574
