Graduate Thesis Or Dissertation

 

Northern goshawk breeding habitat selection within high-elevation forests of southwestern Colorado Public Deposited

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  • The northern goshawk (Accipiter gentilis) is a species of concern in the western United States due to its association with mature structural stage forests. I employed a use-versus-availability study design to quantify the vegetative, physiographic, and landscape variables associated with goshawk breeding habitat selection in the San Juan Mountains of southwestern Colorado. This region of Colorado is characterized by high elevations and dominated by spruce-fir forests. I documented 41 goshawk nest territories on the Rio Grande and San Juan National Forests and compared them to random sites. I constructed logistic regression models at multiple spatial scales and employed Akaike’s Information Criterion (AIC) to select the most parsimonious models. Of the models evaluated for the nest-site-scale analysis, there were four top competing models that all contained canopy closure and crown basal height as explanatory variables. Two of the four competing models also contained slope, and two contained the presence of aspen. Increased canopy closure, higher crown basal height, and flatter slopes increased the relative odds of a site being used for nesting. The presence of at least one aspen tree within the stand increased the relative odds of use by more than 5 times. The multi-scale model set contained two top competing models. In both models, greater canopy closure,higher understory crown basal height, and greater distance to edge increased the odds of goshawk use. Model results suggested that it was 59% less likely that a goshawk would select a site centered on a spruce-fir stand than one centered on other available forest types. In southwestern Colorado, stands with high probability of use by goshawks included areas of mature structural stage forest with canopy closure ≥ 40%, open understory, slope ≤ 20%, located ≥ 200 meters from a non-forest edge. Additionally, mixed conifer and spruce-fir stands containing ≥ 10% aspen canopy cover were more likely to contain goshawk nests.
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