Winter nocturnal roost selection by a solitary passerine bird, the Great Grey Shrike Lanius excubitor

Abstrakti

The night roost selection of the Great Grey Shrike Lanius excubitor, was investigated in a farmland landscape in western Poland between the winters 2002/3 and 2004/5. In total, 24 territories were surveyed and 39 night roost sites detected, with willow Salix spp. bushes being the most frequently used roost. The number of roosts varied between one and four per territory. The number of roosting perches within a given bush was significantly corre-lated with the overall bush volume. Shrikes selected bushes that had a large volume, had a high density of stems, and were isolated from other bushes or trees. Micro-habitat patterns of night-roost selection suggested that the roosts fulfilled two main functions: thermoregulation and predator avoidance. However, a trade-off may have existed be-tween minimizing thermoregulatory costs and avoiding potential predators, because shrikes selected bushes for roosting. In contrast to Great Grey Shrikes e.g. in Finland, birds in the studied population avoided impaling and caching prey in roosting sites, which might be a strategy to avoid detection by predators or might reflect differences in climate. The availability of roosting sites might be an important factor in habitat selection for win-tering Great Grey Shrikes.