UNIFORMITY IN RELATIVE HABITAT SELECTION BY BUTEO LINEATUS AND B. PLATYPTERUS IN TWO TEMPERATE FOREST REGIONS

Abstract

I have examined nest site habitat use and selection by two woodland hawk species, Buteo platypterus (Broad-winged Hawk, BWH), and b lineatus (Red-shouldered Hawk, RSH). The hypothesis tested was that species select similar nesting habitat in dissimilar regions after accounting for differences in habitat availability. Study sites were located in northeast Wisconsin {WI) and in western Maryland {MD). Twenty-seven characteristics were measured at active nest sites from 1978 through 1982. Also, random samples were collected to estimate habitat availability. Sample sizes were: 87 MD BWH, 34 WI BWH, 30 MD RSH, 22 WI RSH, 100 MD random, and 73 WI random. The two regions differed in structural features of the available habitat, and both species selected only portions of the available habitat within each region. Also, habitat use by BWH and RSH differed between regions. To determine whether relative habitat selection differed between regions for each hawk species, I adjusted for regional differences -u-sing a series of 'Z' score rescalings of the availability data. Study area differences were eliminated by these transformations. The resultant data vectors were then applied to the specific hawk data sets for tests of habitat selection uniformity. Relative habitat selection was uniform between regions. For the BWH, only two of 18 rescaled variables were different between regions. Three of 18 rescaled variables were different between regions for RSH. I contend that these two species have uniform patterns of habitat selection. Differences in habitat use between regions may merely reflect habitat availability related to differences in scale between regions.