Habitat variables explain Loggerhead Shrike occurrence in the northern Chihuahuan Desert,but are poor correlates of fitness measures |
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| Authors: | Véronique St-Louis Anna M Pidgeon Murray K Clayton Brian A Locke Dallas Bash Volker C Radeloff |
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| Institution: | (1) Department of Forest and Wildlife Ecology, University of Wisconsin, Madison, 1630 Linden Dr., Madison, WI 53706, USA;(2) Department of Statistics, University of Wisconsin, Madison, WI 53706, USA;(3) DPW, Division of Environment, IMWE-PWD-E, Bldg 624, Pleasanton Rd, Fort Bliss, TX 79916, USA;(4) Present address: Environmental Change Initiative, Brown University, Box 1951, Providence, RI 02912, USA |
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| Abstract: | Conservation efforts should be based on habitat models that identify areas of high quality and that are built at spatial scales that are ecologically relevant. In this study, we developed habitat models for the Loggerhead Shrike (Lanius ludovicianus) in the Chihuahuan Desert of New Mexico to answer two questions: (1) are highly used habitats of high quality for shrikes in terms of individual fitness? and (2) what are the spatial scales of habitat associations relevant to this species? Our study area was Fort Bliss Army Reserve (New Mexico). Bird abundance was obtained from 10 min point counts conducted at forty-two 108 ha plots during a 3-year period. Measures of fitness were obtained by tracking a total of 73 nests over the 3 years. Habitat variables were measured at spatial scales ranging from broad to intermediate to local. We related habitat use and measures of fitness to habitat variables using Bayesian model averaging. We found a significant relationship between bird abundance and measures of fitness averaged across nesting birds in each plot (correlation up to 0.61). This suggests that measures of habitat use are indicative of habitat quality in the vicinity of Fort Bliss. Local- and intermediate-scale variables best explained shrike occurrence. Habitat variables were not related to any measures of fitness. A better understanding of the factors that limit individual bird fitness is therefore necessary to identify areas of high conservation value for this species. |
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