Despite a tendency for males of polygynous bird species to show bright or elaborate plumage, comparative analyses have failed to show any consistent relationship between male brightness or plumage dimorphism and the form of breeding systems. Here we argue that this may be partly because the opportunity for sexual selection varies between species showing serial or seasonal monogamy and life-long monogamy. In waterfowl, both the brightness of male plumage and sexual dimorphism in colouration vary between these categories of monogamy. Other ecological factors related to male brightness or plumage dimorphism include male assistance in protecting young, latitude and an index of parasite sharing. The adaptive significance of these trends is discussed.
I'herr \\as considerable variation in winter territoriality among Mute Swan pairs around Oxford, though most pairs maintained their territories for at least half the winter. Variation was associated with temperature and with territory quality pairs left their territories most commonly during the coldest months of the %,inter, and pairs on good territories, with abundant vegetation and accessible pasture. stayed longer on territory than those on poor territories with sparse vegetation and little pasture. -4s in other species, exclusive territorial defence was maintained at intermediate levels of resourcc availability. and flocks were able to settle on a few particularly good territories. Circumstantial evidence suggested that \\inter territories may be maintained not only to provide an adequate food supply for thc owners but also to ensure access to a brerding site by preventing other individuals from taking over the area.
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