Experimental evidence that female spotless starlings show colour and type preferences in the feathers carried to their nests

Abstract

Female spotless starlings (Sturnus unicolor) frequently bring feathers to the nest, especially during egg laying and incubation. Previous studies indicate that these feathers may not only be involved in nest thermoregulation but can also act as a sexual signal possibly indicating quality. Studies show that female starlings increase feather carrying to the nest as response to male displays, and that these feathers are not randomly placed in the nest, but arranged to maximize their reflectance. The aim of this study was to determine if females exhibit a preference for feathers of certain colours that show higher conspicuousness or show a preference for colours less available in the field. For this, during the incubation period of the nests (between days 3 and 10 after clutch completion), we selected 9 test points in a spotless starling breeding population of 250 nests in Soto del Real (Madrid). In each point, we placed 100 commercially available goose artificially coloured feathers (20 blue, 20 brown, 20 red, 20 white and 20 yellow) of two different types (1/2 flight, 1/2 contour feathers). Every day we replenished the feather points and after five days we checked all nest boxes surrounding the selected points (104 in total). We found 496 experimental colour feathers in 29 different nests. We found that female starlings significantly preferred white feathers to the rest of colours and avoided picking red and blue feathers. Regarding the type of feather, experimental contour feathers were significantly more frequently found in nests than flight feathers. Our results indicate that females prefer feathers that maximise their thermoregulatory function -i.e. contour feathers- while exhibiting a strong preference for highly reflective feathers that contrast with the background colours of the nest and the substrate where they were collected from. In addition, females seem to avoid feathers of conspicuous colours that are rarely found in the study site.