Habitat Selection in Birds: On the Presence of Other Bird Species with Special Regard to Turdus pilaris

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Abstract
Habitat selection in passerines and Columba palumbus was studied in relation to the occurrence of T. pilaris, using data from repeated surveys (498) in 4 forest localities in Norway, 1970-1978. Some species showed a close association with T. pilaris colonies, they changed their annual distributions within the individual areas in phase with this species and also increased in numbers in an area in which this protector population increased after the experimental removal of the most important nest predator (Corvus corone). These were primarily species represented in subalpine and northern areas. Some species showed lower association with T. pilaris than expected by chance and tended to decrease in numbers in the area in which the crow population had been reduced. These were primarily a species with a southern distribution not found in subalpine areas, and was probably due to interspecific competition. The breeding strategy of the subalpine-northern species may be to take advantage of T. pilaris (which also is subalpine-northern) as a protector, and they nest in clumps and have a short prelaying period. Presence of C. corone may increase bird species diversity of the community; the reverse was found if T. pilaris was present.