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Nest site choice in relation to the presence of old nests and cavity depth in the starling Sturnus vulgaris

Hole nesting birds are frequently faced with the problem of old nests from previous breeding seasons in their nest cavities. Many studies investigated birds' site selection preferences, but mostly in connection with the level of ectoparasites occurring in old nests. But the presence of old nest material in a cavity may also result in a shallower nest site, making the eggs or nestlings more vulnerable to predators. However, the presence of an old nest in a cavity may function as a cue for site safety. Nest site choice of the starling Sturnus vulgaris in relation to cavity depth and the presence of old nests was studied for four years. Nest boxes with or without old nests and of varying depths were used in field experiments. This study found that the starling prefers deeper nest boxes and those without old nests. Nest sites with old nest material could have been avoided either because of the presence of ectoparasites or inappropriate cavity depth. It seems that the starling does not assess site quality by the presence of an old nest. However, the results of this study did not show which of these factors was the stronger indicator for the birds' preference of a site. The presence of old nests and cavity depth on starlings' breeding ecology and ethology are discussed.