Ardea
Official journal of the Netherlands Ornithologists' Union

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Matthysen E. (1986) Some observations on sex-specific territoriality in the Nuthatch. ARDEA 74 (2): 177-183
A small population of colour-banded Nuthatches was observed continuously from August 1982 until June 1985. Confrontation experiments with a live decoy at artificial feeding sites showed that territorial birds reacted most strongly to the presence of intruders of their own sex. Intruders of the other sex were sometimes tolerated without aggressive behaviour. Males and females showed differences in behaviour towards intruders of their own sex. Reactions were also more aggressive in autumn than in spring. Trios are situations in which an individual bird shares the territories of two other birds and defends a 'double' territory with a partner in each half of it. Most trios are formed when a territorial vacancy, caused by disappearance of a pair member, is invaded by a neighbouring bird which does not leave its former territory and partner. Sharing two territories at a time may bring short-term or long-term advantages in access to food or shelter, insurance of a mate or improvement in territory and/or mate quality. About half of the disappearances of paired Nuthatches resulted in trios. Sex-specific aggression and the occurrence of trios both support the hypothesis that territorial behaviour of the Nuthatch is highly sex-specific, with territory boundaries of male and female coinciding in most, but not all cases.


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