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Résumé :
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Summary. 1 This paper deals with the Great Tit, Blue Tit, Marsh Tit, Willow Tit, Black-capped Chickadee and Plain Tit. All species are territorial in the breeding season, but show a wide variety of territorial behaviour in winter, correlated with their food supply. 2 The territorial behaviour of each species is described briefly. Sizes of territories are given and differences between and within the species are discussed. 3 The reproductive rate of Great Tits varies inversely with their density. If this is general among tits it could give sufficient selective advantage for the persistence of territory. 4 By limiting density, territory could reduce intra-specinc competition for mates, nest-sites and food, or check disease and predation. There is probably no single, outstandingly important function of territory common to all tits. 5 Great Tits, and perhaps other species, looking for a place to breed prefer certain habitats, but avoid crowding. 6 The value of the distinction between territory limiting density and merely spacing out the pairs is questioned. There is some evidence that territory may limit density.
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