Irish scientists unravel the mystery of the 'pink swans'

In a paper to be published in the international journal Wildfowl UCC researchers, describe for the first time, the cause of pink coloration in Mute swans which has been observed in many parts of Ireland, Britain and North America. 

‘Symmetrical salmon-pink colour was first evident on the wing feather tips and then spread to the entire wing as the year progressed, darkened as winter approached, and sometimes developed to a brown colour’ according to Professor John O’Halloran the study director and Head of the School of Biological, Earth and Environmental Science (BEES) at the University.

Unfortunately, ‘the affected feathers tended to become brittle, fragmented and lose their ability to repel water and the plumage could no longer function and some birds died from hypothermia’. Surveys made at nine sites in Britain and Ireland found between 12–85% of swans with pink coloration.  The highest prevalence occurred amongst flocks dependent on artificial food in eutrophic water bodies.

Feather samples (white and pink), bill swabs and swabs of preen gland oil collected from swans, and also pink fungus isolated from bread samples, were cultured and subjected to analysis, to identify organisms and pigments. Salmon-pink Chrysonilia sitophila fungus colonies developed on agars inoculated with samples from pink swans and from the bread sample, but were absent from control swans.

The pigments in pink feathers were generally consistent with those found in C. sitophila, indicating that C. sitophila is the most likely agent responsible for the pink colour on swan plumage.

‘The evidence from this study suggests that C. sitophila is acquired through exposure to contaminated food via the bill and is preened onto the plumage’ says O'Halloran.

A layer of environmental contaminants and debris that coats the plumage of swans inhabiting eutrophic water bodies may provide a substrate for fungal growth and added to the problems for the swans.

‘The clear message from this study is to feed swans natural foods not stale bread- contaminated with fungi’ according to O’Halloran.