Roost sites of radio-marked Mexican spotted owls in Arizona and New Mexico: sources of variability and descriptive characteristics

Abstract

To increase understanding of roosting habitat of Mexican Spotted Owls (Strix occidentalis lucida) and factors that influence use of roosting habitat, we sampled habitat characteristics at 1790 sites used for roosting by 28 radio-marked Mexican Spotted Owls in three study areas in Arizona and New Mexico. We explored potential patterns of variation in roost-site characteristics by estimating similarity among all possible pairs of roost sites and summarizing patterns in these similarity estimates using a linear model. Factors in the model included owl identity and season. We conducted these analyseswithin study areas, because habitat characteristics differed among study areas. We used a repeated-measures model which assumed that similarity estimates computed between roost sites of the same owl or pairs of owls were correlated. This model significantly improved model goodness-of-fit over a null model assuming no such correlation structure. Similarity estimates were relatively high (0.744-0.775) in all three study areas, suggesting consistent patterns of selection among owls within areas. Owl and season effects were relatively small but detectable in all study areas, with the relative magnitude of these effects differing among areas. The seasonal effect was greatest in the area dominated by pine-oak forest and relatively slight in two areas where owls roosted primarily in mixed-conifer forest. Relative to areas where owls roosted in mixed-conifer forest, roosts in pine-oak forest occurred on moderate slopes, on southwest to northwest aspects, and were less concentrated on lower portions of slopes. We suspected that much of this difference reflected differences in stand-development processes in different forest types. This suggested that land managers should incorporate knowledge of such patterns in different forest types and topographic locations in planning decisions involving management of Spotted Owl habitat.

Citation

Ganey, Joseph L.; Block, William M.; King, Rudy M. 2000. Roost sites of radio-marked Mexican spotted owls in Arizona and New Mexico: sources of variability and descriptive characteristics. Journal of raptor research. 34(4): 270-278