Abstract
Colours that underlie animal pigmentation can either be permanent or renewable in the short term. Here we describe the discovery of a conspicuous salmon-pink colouration in the base of bustard feathers and down that has never been reported because of its extraordinarily brief expression. HPLC analyses indicated that its constituent pigments are coproporphyrin III and protoporphyrin IX, which are prone to photodegradation. Accordingly, an experimental exposure of feathers of three bustard species to sunlight produced a rapid disappearance of the salmon-pink colouration, together with a marked decrease in reflectance around 670 nm coinciding with the absorption of porphyrin photoproducts. The disappearance of the salmon-pink colouration can occur in a period as short as 12 min, likely making it the most ephemeral colour phenotype in any extant bird. The presence of this colour trait in males performing sexual displays may thus indicate to females a high probability that the males were performing their first displays and would engage in their first copulations in the breeding season. In dominant males, sperm quality decreases over successive copulations, thus porphyrin-based colouration may evolve as a signal of virginity that allows females to maximize their fitness in lek mating systems.
Highlights
Representing the most rapidly decaying visual trait in an animal and probably in any living organism
The specimen exhibited a conspicuous salmon-pink colouration in contour feathers that was only visible when the plumage patch was examined and the base of feathers was exposed (Fig. 1a). We detected this colouration in the nuptial plumage of an adult male great bustard that was found dead near La Albuera (Southwest steppe-land birds in Andalusia (Spain)) in April 2016 (Fig. 1b)
The salmon-pink portion of these feathers exhibited strong red fluorescence under UV light (Fig. 1d), suggesting that the colour was generated by porphyrins
Summary
This novel salmon-pink plumage colouration was first noticed by one of us (R.M.) when a recently shot female great bustard Otis tarda was found dead in coastal Dobrudzha, close to Durankulak Lake (Northeast Bulgaria), in January 2012. The specimen exhibited a conspicuous salmon-pink colouration in contour feathers that was only visible when the plumage patch was examined and the base of feathers was exposed (Fig. 1a) We detected this colouration in the nuptial plumage of an adult male great bustard that was found dead near La Albuera (Southwest Spain) in April 2016 (Fig. 1b). The salmon-pink colour of great bustard plumage is only visible in the base of the feathers (Figs 1 and 3b and electronic supplementary material, movies S1–S2), the sexual exhibition of great bustard males is extraordinarily exaggerated and entirely visual[33]. Females assess the plumage characteristics of males[32] from a very short distance (Fig. 5), a situation in which they can potentially observe the salmon-pink colour of male feathers (Fig. 3b) As this colour trait rapidly decays under sunlight, males can only use it during a few display bouts, functioning similar to a sand clock. Our findings show that the levulinic route leads to conspicuous and ephemeral integument colourations, opening a new avenue for the study of visual communication in which the expression duration of colour may have a key evolutionary role
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