The difficult challenge of accurately recording iris colour in birds revealed through the lens of specimens of Australia's Spinifex Pigeon (Geophaps plumifera)

Abstract

Museum collections of birds are a key source of data on the colours of ‘soft parts’, e.g. legs, feet, bill (maxilla, mandible), wattles, periocular skin and, our focus here, the iris of the eye. However, subjective descriptions of soft parts' colours have long plagued their use, whether in research or in illustrations of birds. We document a case where reasonable doubt about the accuracy of iris colour recorded more than 50 years ago in several taxonomically important series of specimens of the Australian Spinifex Pigeon Geophaps plumifera is probably unresolvable. This doubt clouds the downstream use of the specimens in a complete understanding of geographical and temporal variation, and taxonomy. We discuss how ornithologists may apply methods now readily available that will enable more rigorous recording of soft parts' colours, despite many valid limitations. This especially applies in situations where existing knowledge dictates care, such as in already known zones of taxonomic intergradation or when colours known to be unusual and unexpected are seen.