Nest decoration: Black feathers prevent Crested Mynas from nest usurpation

Nests are important structures for birds to raise their offspring and for signaling. Many birds incorporate feathers into the nest, since feathers were traditionally thought to serve the function of insulation. Hypotheses in recent years have considered that some birds place feathers in conspicuous locations in the nest for decoration to trigger a fear response in the competitors. In this study, we investigated whether decorative feathers could deter nest usurpation by Crested Mynas (Acridotheres cristatellus) by manipulating nest box contents. The results revealed that Crested Mynas preferred black feathers to white feathers as decorations and occupied nest boxes decorated with black feathers significantly less than those decorated with white feathers, suggesting that black decorative feathers in the nest could be more effective in preventing nest usurpation by Crested Mynas and that white decorative feathers may have other functions. The black feathers in the nest are prominently placed at the edge of the nest to convey the message that "this nest is occupied" or "the owner of this nest has been preyed upon" to visitor Crested Mynas, thus effectively preventing them from usurping the nest at a later stage.