Starlings have difficulty in detecting dot symmetry: Implications for studying fluctuating asymmetry

Small differences between the left and right sides of otherwise symmetric traits are related to developmental instability and can indicate how well the genome is suited to current developmental conditions. As these small asymmetries (termed fluctuating asymmetry, or FA) can reveal how well the genome is suited to the environment, researchers have postulated that FA can indicate fitness and be used by other animals as a visual cue to fitness in sexual and social encounters. Despite these claims, we know little about how animals perceive subtle symmetry differences and whether such cues could be used in nature. Here we investigate the symmetry detection abilities of wild caught European starlings Sturnus vulgaris. We presented symmetric and asymmetric images, that resemble the complex dot patterns commonly observed on starling chest plumage, through a series of operant learning sessions. Asymmetric images were produced by introducing a 40% dot number asymmetry. Following extended learning sessions, the birds were not able to accurately discriminate symmetry from asymmetry. Although complex dot patterns (similar to those studies here) are common in nature, it appears unlikely that starlings (and perhaps other birds) could use number asymmetry in such traits as a direct cue to mediate behavioural interactions.