Bill color is dynamic across the breeding season but not condition-dependent in Atlantic puffins

Abstract

AbstractSexually monomorphic species have been historically overlooked in the sexual/social selection literature, but there is growing evidence that mutual ornamentation can be driven by selective forces such as mutual sexual selection or selection for individual recognition. Examining the properties of a trait may elucidate which forces most likely play a role, especially when comparing the characteristics of quality and identity traits. Atlantic puffins(Fratercula arctica)are an example of a mutually ornamented monomorphic species, where both males and females display a bright orange-red bill and orange gape rosette during the breeding season and are ornamented to similar degrees. In this study, we investigate whether the properties of the colorful bill and rosette, specifically lability across the breeding season and condition-dependence, more closely align with signals of quality or identity. Our findings support prior work that the bill is sexually monochromatic from an avian visual perspective. We also determined that the bill changes in a discriminable way within individuals and is especially dynamic in the fleshy cere and rosette. However, no metric of color on any region of the bill or rosette were significantly related to current body condition. Ultimately, we argue that bill color likely functions as a quality signal, although further study is needed to determine which aspect of quality coloration signals, if not condition. These results provide a basis for experimentally testing the signal value of the colorful bill in Atlantic puffins, and more broadly, a framework for investigating the properties of mutual ornamentation in avian species.Lay summaryThe properties of a colorful trait inform its potential function as a signal. We investigated whether the Atlantic puffin’s colorful bill could reflect an individual’s identity or quality. Because bill color changes within the breeding season, this feature is not stable enough to reliably signal identity. Bill color is also not related to a common proxy of quality (body condition) but may communicate another aspect of quality such as foraging or parenting ability.