WINTER TERRITORIES AND NIGHT ROOSTS OF NORTHERN SHRIKES IN IDAHO

To study the winter ecology of Northern Shrikes in southwest Idaho, I observed the activities of six color-banded and six radio-tagged shrikes over the winters of 1988-1989 and 1989-1990. These shrikes occupied winter territories that averaged 216 ha in size (minimum convex polygon method). Over one-half of the activity of each shrike was confined to a core area of approximately 50 ha. Five of nine individual Northern Shrikes perched in or hunted within mesic areas significantly more than expected and four of the nine utilized grasslands significantly less than expected. Linear habitats such as riparian corridors and rimrock outcroppings appeared to be important to wintering shrikes since the former provided night roost habitat whereas the latter provided warm and productive areas for prey populations. I located 10 night roosts of Northern Shrikes. All were in deciduous shrubs with many small stems. Shrikes may depend upon these roosts for thermal protection and escape from predators.