Colour polymorphism in the common buzzard : evolution and life history consequences
The detrimental effects of inbreeding are well known, and they have been shown to be associated with lower levels of reproductive success, higher levels of parasitism and differences in disease susceptibility. To better understand large fitness differences between morphs in the colour polymorphic common buzzard, Buteo buteo, we investigated differences in the levels of internal relatedness between morphs. As the common buzzard mating system is non-random and the light and dark morph individuals are less abundant than the intermediates, it could be the case the extreme colour morph individuals are more inbred. However, no differences were found in levels of inbreeding. In birds, the physiological and behavioural consequences of colour polymorphisms are not widely known. Here we used an experiment to investigate the effect of this melanin-based polymorphism on nest defence behaviour in the common buzzard. Among males, light morphs were found to be significantly more aggressive to a perceived threat of nest predation than either intermediate or darkly coloured birds, while there was a non-significant tendency for the reverse among females. The level of aggression observed for each member of a pair was independent of the level of aggression shown by the other member. These results illustrate that polymorphisms can be associated with alternative reproductive tactics in birds, and suggest a possible link between the biochemistry of melanin production and individual behaviour. For most species living in seasonal environments, timing is an important determinant of the success of a breeding attempt. Individuals also face a trade off between current and future reproduction. Here we investigated whether colour morphs differed in their timing of breeding. Light-light and dark-dark pairs were found to breed earlier than the population mean, with light-dark pairs fledging chicks slightly later. Differences in reproductive strategies between morphs may account for the observed differences.