Analysis of Bald Eagle spatial use of linear habitat

Several techniques are available for areal analysis of animal locations but few are applicable to those that use linear (i.e., riparian) habitats. Bal d Eagles (Haliaeetus leucocephalus) often are associated with rivers and co ncentrate perch sites near shorelines. Distribution of cumulative proportio n of perches by distance from most recently active nest sites determined by radio tracking were used to compare spatial use among five adult Bald Eagl es breeding along the Snake River, Wyoming. Spatial Use Indicators (SUIs) w ere developed from logistic regression parameters in attempts to: (1) under stand and model underlying processes from which the data may have emerged, (2) compare with simple descriptive statistical techniques to evaluate util ity for presenting a clear, accurate representation of spatial use differen ces among eagles, and, (3) relate measures of eagle spatial rise with long- term productivity of breeding areas. Distance Indicator (DI) was the distan ce from the nest including 50% of all detected perches used by a radio-tagg ed eagle and was representative of the size of the range. Slope Indicator ( SI) was the slope of the fitted logistic regression curve at the DI (inflec tion point). SI was an indicator of linear dispersion of perch sites within the breeding area. Bald Eagles associated with more productive (>0.77 youn g per occupied nest over 11 years) breeding areas perched closer to nest si tes (similar DIs) than eagles of their respective gender in a breeding area s of low productivity (<0.77 voting per occupied nest). Male Bald Eagles in highly productive breeding areas dispersed perch sites more evenly through out the breeding area (flat SI) than a male in a low production breeding ar ea, while the opposite was true for females. Spatial use profiles derived f rom analysis of mean and confidence intervals and median and Interquartile Ranges were not as descriptive or illustrative of individual or group simil arities or differences as SUIs. Logistic analysis suggested Zone 11 (primar y foraging zone) limits recommended in regional Bald Eagle management plans may need to be extended to maintain performance of highly-productive pairs nesting along rivers. SUIs derived front logistic regression models of dis tance of locations from important habitat components may be indirect indica tors of habitat quality and useful tools for describing and comparing spati al use of linear habitats of other species.