Nonrandom pairing by male barn owls (Tyto alba) with respect to a female plumage trait

In socially monogamous species it is rare for females to bemore intensely colored than males. The barn owl (Tyto alba)is one of the exceptions, as females usually exhibit more andlarger black spots on the plumage. The evolution of sexual dimorphismin plumage traits is commonly assumed to be the result of sexualselection. I therefore examined the prediction that male barnowls do not pair randomly with respect to female plumage spottinessduring a 5-year study in Switzerland. The prediction was supported,as males that changed mates acquired a new female that was similarlyspotted to the previous one, and pairing with respect to plumage spottinesswas positively assortative. Significant repeatability in male pairingwas presumably neither the consequence of sharing the same habitats withfemales displaying a given plumage spottiness nor of morphological characteristicsof the males that could influence mate sampling. A resemblance inplumage spottiness between the mates of sons and of their fathersuggests that repeatability could have resulted from sexualimprinting and/or heritable variance in male preference forspotted females. To test whether males assess female plumagespottiness, I either cut off black spots or small pieces of feathersbut not the spots of already mated females. Males mated to females withreduced plumage spottiness fed their brood at a lower cadencyand achieved a lower reproductive success than other males.This experiment further suggests that female plumage spottinessis a stimulus for males.