TERRITORY IN THE THICK‐BILLED NUTCRACKER NUCIFRAGA CARYOCATACTES.

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Summary. The main features of the territory in the Thick‐billed Nutcracker are:‐ (a) the territory is kept for life and inhabited throughout the year; (b) the special food, nuts, is stored in the territory; (c) song, copulation, nest‐site selection and nest‐building take place only in the territory; (d) territories examined were 11.2–14.9 hectares, averaging 32.7 acres, believed to be the normal size in Sweden. There is no clear evidence that the territory has the function of securing more than a certain amount of food other than stored. The territory is respected by other Nutcrackers as to its main functions, while simple visits by other Nutcrackers and ceremonial gatherings in the territory are tolerated. Both territory‐holders attack intruders that try to take nuts but as they do not chase them out the behaviour is not regarded as truly territorial behaviour. The territory is proclaimed by the calls, the song being exclusively sexual. Unmated birds have not been recorded with territorial behaviour. When the special food is limited and the nesting habitat ample, the population is limited by the amount of the special food; but when the special food is abundant and the nesting habitat limited, over‐crowding seems to be prevented by territorial behaviour. It is suggested that the function of territory in the Nutcracker is to give the holders a well‐known refuge from predators, to serve as a food storing place, and by spacing out to prevent these positive qualities from reduction by overcrowding.