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 be more intensely colored than males. The barn owl (Tyto alba) is one of the exceptions, as f emales usually exhibit more and larger black spots on the plumage. The evol ution of sexual dimorphism in plumage traits is commonly assumed to be the result of sexual selection. I therefore examined the prediction that male b arn owls do not pair randomly with respect to female plumage spottiness dur ing a 5-year study in Switzerland. The prediction was supported, as males t hat changed mates acquired a new female that was similarly sported to the p revious one, and pairing with respect to plumage spottiness was positively assortative. Significant repeatability in male pairing was presumably neith er the consequence of sharing the same habitats with females displaying a g iven plumage spottiness nor of morphological characteristics of the males t hat could influence mate sampling. A resemblance in plumage spottiness betw een the mates of sons and of their father suggests that repeatability could have resulted from sexual imprinting and/or heritable variance in male pre ference for spotted females. To test whether males assess female plumage sp ottiness, I either cut off black spots or small pieces of feathers but nor the spots of already mated females. Males mated to females with reduced plu mage spottiness fed their brood at a lower cadency and achieved a lower rep roductive success than other males. This experiment further suggests thar f emale plumage spottiness is a stimulus for males.