The role of light in structuring the ecological niche remains a frontier in understanding how vertebrate communities assemble and respond to global change. For birds eyes represent the primary external anatomical structure specifically evolved to interpret light, yet eye morphology remains understudied compared to movement and dietary traits. Here, I use Stanley Ritland’s unpublished measurements of transverse eye diameter from preserved specimens to explore the ecological and phylogenetic drivers of eye morphology for a third of terrestrial avian diversity (N = 2777 species). Species with larger eyes specialized in darker understory and forested habitats, foraging manoeuvres and prey items requiring long-distance optical resolution, and were more likely to occur in tropical latitudes. When compared to dietary and movement traits eye size was a top predictor for habitat, foraging manoeuvre, diet, and latitude, adding 9 – 29% more explanatory power. Eye size was phylogenetically conserved (lambda = 0.90), with phylogeny explaining 61% of eye size variation. I suggest that light has contributed to the evolution and assembly of global vertebrate communities and that eye size provides a useful predictor to assess community response to global change.

The novel contribution of this dataset is the matrix of eye size measurements for 2804 species of terrestrial birds extracted from Stanley Ritland's unpublished dissertation (Ritland 1982, University of Chicago). SR collected all measurements from specimens of whole eyes preserved in formaldehyde and/or alcohol using 0.05 mm Vernier callipers. The attached dataset includes the original raw measurements collected by SR (per specimen) as well as species-specific averages and residuals correcting for body size allometry (using phylogenetic least squares regression) for two dimensions of eye size: transverse diameter (TD) and axial diameter (AD). The raw data matrix also includes measurements for cornea diameter. Please see the associated publication for details on species and analysis.

The remaining databases are composed of subsets from previously published datasets on avian ecomorphology, dispersal correlates, and foraging traits (Wilman et al. 2014, Pigot et al. 2020, Sheard et al. 2020). The classification of habitat (forest specialist v. non-forest) is based on Bird Life International habitat classifications. Please see the associated publication for details.

The R scripts allow full reconstruction of the analyses described in the associated publication.

Please see the 'Read Me.doc' file for further explanations of all files.