Interannual repeatability of eggshell phenotype in individual female common Murres (Uria aalge)

The recognition of own progeny is critical in group-living organisms that provide parental care for their young. The colonial seabird Common Murre (Uria aalge (Pontoppidan, 1763); also known as the Common Guillemot) does not build a nest, so direct cues must be available for the parents to recognize their own egg. However, only anecdotal evidence exists that, as seen in other avian lineages where examined, eggshells of Common Murres are also consistent in most aspects of their appearance between different breeding attempts by each female. Using digital photography, we quantified several eggshell traits of a handful of captive Common Murres across multiple years. Individual female Common Murre eggs were significantly repeatable in background colour, maculation coverage, spot shape, and shell size. Laying individually consistent and recognizable eggshells across breeding attempts may benefit Common Murres by reducing both the cost of relearning and the risk of misidentifying their own eggs. More generally, these data also add to the growing knowledge of individually consistent eggshell genesis by the avian reproductive system.