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

Sensory collectives in natural systems

Groups of animals inhabit vastly different sensory worlds, or umwelten, which shape fundamental aspects of their behaviour. Yet the sensory ecology of species is rarely incorporated into the emerging field of collective behaviour, which studies the movements, population-level behaviours, and emergent properties of animal groups. Here, we review the contributions of sensory ecology and collective behaviour to understanding how animals move and interact within the context of their social and physical environments. Our goal is to advance and bridge these two areas of inquiry and highlight the potential for their creative integration. To achieve this goal, we organise our review around the following themes: (1) identifying the promise of integrating collective behaviour and sensory ecology; (2) defining and exploring the concept of a 'sensory collective'; (3) considering the potential for sensory collectives to shape the evolution of sensory systems; (4) exploring examples from diverse taxa to illustrate neural circuits involved in sensing and collective behaviour; and (5) suggesting the need for creative conceptual and methodological advances to quantify 'sensescapes'. In the final section, (6) applications to biological conservation, we argue that these topics are timely, given the ongoing anthropogenic changes to sensory stimuli (e.g. via light, sound, and chemical pollution) which are anticipated to impact animal collectives and group-level behaviour and, in turn, ecosystem composition and function. Our synthesis seeks to provide a forward-looking perspective on how sensory ecologists and collective behaviourists can both learn from and inspire one another to advance our understanding of animal behaviour, ecology, adaptation, and evolution.

Coloniality and development impact intraclutch consistency of avian eggs: a comparative analysis of the individual repeatability of eggshell size and shape metrics

In oviparous animals, egg morphology is considered an aspect of the extended phenotype of the laying mother and, thus, can be directly assessed for consistency both within and between individual females. Despite a recently renewed interest in the evolution and mechanics of avian eggshell morphology, we still lack a large-scale, comparative understanding of which egg traits are individually plastic and whether individual consistency is shaped by ecological and life history traits at the species level. Here, we aimed to understand whether intraclutch repeatability per se of different eggshell metrics is an evolving trait that responds to selection pressures from socio-ecological contexts across a diverse group of avian species for which clutch-level eggshell morphology data were available to us. Coloniality, ontogeny, and incubation period had significant impacts on the comparative patterns of relative individual repeatability among two egg metrics (i.e., size and shape), whereas other life history traits (including adult size, clutch size, nest type, migration, breeding latitude, host status of brood parasitism) did not have statistical impacts. Our results also demonstrate that individual consistency has a more widespread phylogenetic distribution than expected by evolutionary contingency across avian diversity. Future analyses should also incorporate the effects of intra- and interspecific covariation in other morphological and physiological traits on the evolution of individual consistency, especially those relevant to egg recognition, including eggshell color and maculation.

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

Brood parasitized and/or colonial birds use egg features as visual identity signals, which allow parents to recognize their own eggs and avoid paying fitness costs of misdirecting their care to others’ offspring. However, the mechanisms of egg recognition and discrimination are poorly understood. Most studies have put their focus on individual abilities to carry out these behavioural tasks, while less attention has been paid to the egg and how its signals may evolve to enhance its identification. We used 92 clutches (460 eggs) of the Eurasian coot Fulica atra to test whether eggs could be correctly classified into their corresponding clutches based only on their external appearance. Using SpotEgg, we characterized the eggs in 27 variables of colour, spottiness, shape and size from calibrated digital images. Then, we used these variables in a supervised machine learning algorithm for multi-class egg classification, where each egg was classified to the best matched clutch out of 92 studied clutches. The best model with all 27 explanatory variables assigned correctly 53.3% (CI = 42.6–63.7%) of eggs of the test-set, greatly exceeding the probability to classify the eggs by chance (1/92, 1.1%). This finding supports the hypothesis that eggs have visual identity signals in their phenotypes. Simplified models with fewer explanatory variables (10 or 15) showed lesser classification ability than full models, suggesting that birds may use multiple traits for egg recognition. Therefore, egg phenotypes should be assessed in their full complexity, including colour, patterning, shape and size. Most important variables for classification were those with the highest intraclutch correlation, demonstrating that individual recognition traits are repeatable. Algorithm classification performance improved by each extra training egg added to the model. Thus, repetition of egg design within a clutch would reinforce signals and would help females to create an internal template for true recognition of their own eggs. In conclusion, our novel approach based on machine learning provided important insights on how signallers broadcast their specific signature cues to enhance their recognisability.

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

In dense breeding colonies, and despite having no nest structure, common murres (or guillemots: Uria aalge) are still able to identify their own eggs. Each female murre's egg is thought to be recognized individually by the shell's avian-perceivable traits. This is because the eggshells' visible traits conform to expectations of the identity-signaling hypothesis in that they show both high intraindividual repeatability and high interindividual variability. Identity signaling also predicts a lack of correlation between each of the putative multicomponent recognition traits, yielding no significant relationships between those eggshell traits that are generated by mutually exclusive physiological factors. Using a multivariate analysis across eggshell size and shape, avian-perceivable background coloration, spot (maculation) shape, and spot density, we detected no unexpected statistical correlations between Icelandic common murre egg traits lacking known physiological or mathematical relationships with one another. These results biologically replicate the conclusions of a recent eggshell trait study of Canadian common murres using similar methodology. We also demonstrate the use of static correlations to infer identity signaling function without direct behavioral observations, which in turn may also be applied to rare or extinct species and provide valuable insight into otherwise unknown communicative and behavioral functions.