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One of the most complex and fascinating aspects of grouse and quail biology is their social behavior, particularly that related to reproduction. Natural selection in the quail group has seemingly favored the retention of a monogamous mating system with the associated advantages of maintaining the pair bond through the breeding season. This system allows the male to participate in the protection of the nest, possibly participate in incubation, and later care for the brood. It also provides the possibility, if not the frequent actuality, that the male might undertake the entire incubation or rearing of the first brood, while the female is freed to lay a second clutch and rear a second brood in a single breeding season.
In addition, within the quails may be seen a breakdown of typical avian territorial behavior patterns, probably resulting from the greater survival value of ecological adaptations favoring sociality in these birds. Not only do these fairly vocal species benefit from their mutual alarm signals by remaining together but also their small size and catholic feeding behavior reduce the likelihood that the optimal breeding densities will exceed the carrying capacities of the habitat.
By contrast, in the grouse there is a clear indication that selective pressures have favored the retention of strong territorial behavior, and there is a direct relationship between a male's capacities to establish and maintain a favorable territory and his ability to reproduce successfully. This territoriality perhaps results mainly from the wide variation among males in their aggressiveness and reproductive vigor but also from the possibility that in these species the carrying capacity of the habitat in relation to the population density may be more significant for the species' survival than are the advantages of sociality. Thus, territorial behavior among males is conspicuous in all the grouse species.