For some bird species, colouration and patterning in their plumage is likely to play a vital role in camouflage and crypsis via background matching 1, 4. The plumage colours and patterns that bird species display have fascinated evolutionary biologists for decades, although general explanations for them still often remain elusive 6. Thus, the colour of an individual animal, a population, or a species, is thought to be shaped by complex evolutionary processes that drive and maintain phenotypic variation and genetic diversity in nature 5.
This study suggests that avian morphs may allocate/partition foraging activity by weather conditions/habitat, which maximise their concealment from prey.Ĭolouration has been widely recognised to play an important role in a variety of ecological processes, from camouflage (crypsis) 1 to intraspecific communication 2 and mate choice 3, all of which are likely to be under considerable selective pressure from both natural and sexual selection 4. Our results may also help explain why dark-morphs predominate in this study region, which experiences high rainfall and lower light-levels during the breeding-period. This suggests that different morphs may be better adapted to foraging under different light-conditions, potentially playing a role in maintaining colour polymorphism in this species. Furthermore, we found differential-degrees of habitat selection, with dark-morphs selecting more enclosed habitats compared to white-morphs. As predicted, we found that light-levels influenced foraging behaviour in different ways for morphs: Dark-morphs showed a decrease in foraging with increasing light-levels whereas no relationship was found for white-morphs. We use GPS-tracking data to contrast the foraging behaviour and habitat selection of morphs. We explore this hypothesis in a polymorphic raptor, the black sparrowhawk Accipiter melanoleucus, which exhibits a discrete dark and white-morph. The mechanism for this advantage is proposed to be through enhanced crypsis via background-matching. One hypothesis proposes that different morphs are adapted to different ambient light conditions, with lighter morphs having a selective advantage in bright conditions and darker morphs having advantages in darker conditions.
Colour polymorphism may be maintained within a population by disruptive-selection.