RESEARCH: Waxbill birds have a social ranking based on the redness of their feathers

Researchers have found that the bird, the Common Waxbill (Estrilda astrild), chooses its leader based on the redness of its chest feathers. Leadership is not dependent upon intelligence, or size, or size of its family, or stress tolerance, or aggressiveness, or the wealth of the objects it collects – it is based on the colour of its feathers.

The study, reported in The New Scientist magazine in November 2021, found that a Waxbill’s social rank or dominance is linked to how richly red its chest feathers are. The rich red feathers are thought to be a signal of health. The redder the feathers, the healthier the bird, and the most likely it is to be a strong leader. 

Patricia Beltrao at the University of Porto in Portugal, and her research colleagues, observed dozens of adult Common Waxbills that were captured in a large outdoor netted area.  

The researchers measured the body size of the birds and used digital photography and reflectance spectrophotometry to determine the size and saturation levels of their red-feathered chest patches. The researchers also conducted standard behaviour tests on each bird to assess their intelligence, stress tolerance, and levels of aggression or passivity. Afterwards, they monitored the bird feeders in the netted area to record when each bird recognized another bird as a higher-ranking bird or not. If the bird gave up its place at the feeder, it meant that the other bird was higher-ranking. 

The researchers found that the only obvious factor linking rank and dominance was the saturation level of the red chest feathers. Saturation levels determine the richness of colour. If a colour is pale, it has a low saturation level on the reflectance spectrophotometric scale. 

If a bird has a high saturated red colour, it could indicate that it is healthy enough to spare nutrients in food for pigment use, so the feathers could act as a “badge of honour.” Not even the size of the red patch was a factor in dominance, nor the sex or personality of the bird.

However, Patricia Beltrao said, at this stage, the findings are just a hypothesis, and further research is needed.

Journal reference: Animal BehaviourDOI: 10.1016/j.anbehav.2021.09.011

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