Nape Coloration Varies with Sex, not Age, Among Great Shearwaters Ardenna gravis

Nape coloration in Great Shearwaters (Ardenna gravis) varies significantly with sex, not age, contrary to previous suggestions. A study analyzing 328 birds—through necropsies and colony photographs from Gough Island (South Atlantic) and Massachusetts Bay (USA)—found no significant difference in nape color ratios between age classes, with classification accuracy based on putative variation only at chance levels (52%). However, light-colored napes were more prevalent in adult females in Massachusetts Bay, hinting at a potential sexual function. The research challenges the use of nape coloration as an age indicator and proposes it may instead play a role in mate choice, warranting further behavioral studies.

Wakefield, E. D., Robuck, A. R., Powers, K. D., Ronconi, R. A., Ryan, P. G., & Wiley, D. N. (2025). Nape Coloration Varies with Sex, not Age, Among Great Shearwaters Ardenna gravis Marine Ornithology, 53(1). https://doi.org/10.5038/2074-1235.53.1.1627