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Experimental study of social signaling through delayed plumage maturation in a colony-nesting seabird

Hill, Molly1; Dobney, Sarah2; Fanburg, Liliane3; Mennill, Daniel2; Taylor, Liam31

Research facility: Bowdoin Scientific Station, Kent Island
Published Mar 18, 2026 on Dryad. https://doi.org/10.5061/dryad.kkwh70sh6

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Abstract

Delayed development is a widespread evolutionary strategy that can reduce competition among social animals. Many seabirds exhibit delayed plumage maturation, in which young birds spend years in visually distinct predefinitive plumages before attaining the definitive plumage of adults. Previous work hypothesized that predefinitive plumages may function to reduce aggression towards young seabirds at breeding colonies, an idea known from other lineages of birds as the status signaling hypothesis. We tested this hypothesis with visual stimulus experiments at a breeding colony of American Herring Gulls (Larus smithsonianus). We presented painted models of four different plumage classes (first-cycle predefinitive gull plumage, third-cycle predefinitive gull plumage, definitive gull plumage, and a Canada Goose as a control) and measured the aggressive responses of breeding adults at their nests. Breeding gulls responded with significantly less frequent, lower, and slower aggression toward the first-cycle plumage and control stimuli compared to the definitive plumage. There were no significant differences in response towards the third-cycle plumage compared to definitive plumage. These results provide evidence for a status signaling function of the extensive brown plumage characteristic of first-cycle gulls, which may reduce aggression in foraging flocks, on the wintering ground, or during young birds’ brief visits to colonies. Given the lack of differences in aggressive responses to third-cycle versus definitive plumage, our data do not settle the issue of why third-cycle gulls, which spend more time at colonies than younger birds, also molt in brown, predefinitive plumages. Future research can investigate how immature seabirds—including third-cycle gulls—may combine plumage, posture, and behavior to shift the dynamics of social behavior at breeding colonies.