The modelling of avian visual perception predicts behavioural rejection responses to foreign egg colours

Abstract

How do birds tell the colours of their own and foreign eggs apart? We demonstrate that perceptual modelling of avian visual discrimination can predict behavioural rejection responses to foreign eggs in the nest of wild birds. We use a photoreceptor noise-limited colour opponent model of visual perception to evaluate its accuracy as a predictor of behavioural rates of experimental egg discrimination in the song thrush Turdus philomelos. The visual modelling of experimental and natural eggshell colours suggests that photon capture from the ultraviolet and short wavelength-sensitive cones elicits egg rejection decisions in song thrushes, while inter-clutch variation of egg coloration provides sufficient contrasts for detecting conspecific parasitism in this species. Biologically realistic sensory models provide an important tool for relating variability of behavioural responses to perceived phenotypic variation.

Figure 1

Bivariate scatter plot for observed rejection rates (frequency of ejection and nest desertion combined) of experimental eggs from song thrush nests against predicted rejection rates (p_i) for the model: logit (p_i)=−1.96+−47.65_DIFF(UV)+12.48_DIFF(SWS) in table 1. Behavioural rates and coloured loci correspond to the human-perceived mimetic (square loci) and non-mimetic (diamond loci) experimental colours from Honza et al. (2007). The 1 : 1 line is depicted. The loci A is the ‘orange’-type artificial egg discussed in the text.