Inter-Specific Aggression between the Collared Flycatcher and the Pied Flycatcher: The Selective Agent for the Evolution of Light-Coloured Male Pied Flycatcher Populations?

Abstract

The average plumage colour of the head and back of male Pied Flycatchers varies geographically. Light-coloured males live in sympatry, dark-coloured males in allopatry with the Collared Flycatcher. Because the two species of flycatcher compete for nesting holes, inter-specific aggression may have been a selective agent behind the evolution of light-coloured male Pied Flycatchers. Experiments with stuffed dummies of male Pied Flycatchers showed that male Collared Flycatchers were more aggressive towards a black dummy than towards a light-coloured one. Light-coloured male Pied Flycatchers may avoid attacks by male Collared Flycatchers either because they appear less threatening to the Collared Flycatcher in the competition for nest-holes (i.e. inter-specific status signalling) or because they closely resemble female Collared Flycatchers (i.e. inter-specific female mimicry).