Egg patterns as identity signals in colonial seabirds: a comparison of four alcid species

Abstract

The ability to recognize mates, kin, offspring and neighbors by their individually distinctive traits-individual recognition (IR)-is widespread in animals. Much work has investigated IR from the perspective of the recognizer, but less is known about the extent to which signals have evolved to facilitate IR. To explore this, one approach is to compare putative identity signals among species that differ in life history and extent of IR. In Common Murres (Uria aalge), a colonially breeding seabird, the eggs of individual females are remarkably variable in terms of color and pattern (maculation).Common Murres also appear to recognize their own eggs, leading to the hypothesis that variable egg phenotypes evolved to promote recognizability. However, we lack a quantitative assessment of the egg pattern information in Common Murres and their close relatives. Here, we analyzed images of eggs laid by four alcid species: Common Murres, Thick-billed Murres (Uria lomvia), Razorbills (Alca torda) and Dovekies (Alle alle). We extracted pattern measures believed to be relevant to bird vision and calculated Beecher's information statistic (H s ), which allowed us to compare the amount of identity information contained in each species' egg patterns. Murres, which nest in dense colonies and can recognize their own eggs, have egg patterns with a relatively large amount of identity information compared to Razorbills and Dovekies. Egg recognition has not been demonstrated in Razorbills and Dovekies, whose colonies are less dense. Our results are consistent with the hypothesis that complex patterns of Murre eggs may have evolved to increase individual recognizability.

Egg recognition: The importance of quantifying multiple repeatable features as visual identity signals

“…Offspring recognition is also critical for colonial breeding birds [2,[28][29][30][31][32]. This task may be sometimes challenging, as nests can be placed close to each other in huge and dense colonies on uniform substrates, where birds may easily make mistakes in nest recognition and misdirect their parental care to the broods of conspecifics.…”

Multicomponent shell traits are consistent with an individual recognition function of the appearance of common murre (Uria aalge) eggs: A biological replication study

“…In addition, all of the analyzed eggshell traits had also demonstrated high levels of interindividual variability in the published literature (Birkhead, Thompson, & Biggins, 2017; Birkhead, Thompson, Jackson, et al., 2017; Dale, 2006; Hauber, Bond, et al., 2019). Given that identity signals are expected to be both highly variable between individuals and possess a high degree of genetic determination within individuals, along with a lack of correlation between their multicomponent signals (Tibbetts & Dale, 2007), we consider our new results here to provide further evidence for the functionality of maculation shape, spot density, eggshell size and shape, and avian‐perceivable background coloration as possible identity signals for common murre eggs (Quach et al., 2020).…”

“…This is surprising, as there might be more correlations between eggshell background coloration traits and maculation traits within murre eggs. For example, previous studies suggest correlations between background coloration and maculation eggshell traits for the thick‐billed murre (Gaston & Nettleship, 1981; Quach et al., 2020). Additionally, there have been reports of a positive correlation between protoporphyrin and biliverdin concentrations in eggshells of different avian species (the two pigments responsible for aspects of eggshell coloration; Cassey et al., 2012).…”

“…For instance, the related razorbill ( Alca torda ) is a colony‐nesting seabird which displays poor egg recognition abilities (Birkhead, 1978) and, thus, razorbill eggshells would not be expected to possess the characteristics of negatively frequency‐dependent selection recognition trait distribution (Tibbetts & Dale, 2007). Without these selection pressures, then we may expect a higher degree of association between visible eggshell characteristics of species without egg recognition abilities, in comparison with species that do possess these abilities (Quach et al., 2020).…”

“…High interindividual variation in perceivable traits between focal subjects is a diagnostic property of identity signals; that is, traits used to communicate about and recognize a specific individual (Tibbetts & Dale, 2007). Because of this, it is suspected that many of the variable common murre eggshell traits may be identity signals and, thus, play a critical role in the accurate egg recognition abilities of murre parents (Hauber, Bond, et al., 2019; Quach et al., 2020). In comparison, the common murre's sister species, the thick‐billed murre ( Uria lomvia ), that breeds in less densely packed colonies has lower avian‐perceivable egg trait variabilities between individuals (Quach et al., 2020) and, in turn, poorer behavioral egg recognition than that of the common murre (Gaston et al., 1993).…”