Spatial and temporal patterns of Bald Eagle (Haliaeetus leucocephalus) winter habitat use along the Upper Mississippi River corridor
Authors:   , Schmitz Ryan 
Published: February 2023

From March 1999 through February 2006, satellite transmitters were placed on 13 wild-caught individuals of the Bald Eagle (Haliaeetus leucocephalus) in southwestern Wisconsin. These individuals (6 males, 7 females, 11 adults, 2 immatures) were tracked along the Upper Mississippi River corridor during the winters of 1999 through 2006. The objectives of my study were to: 1) estimate winter home range size and to compare home range size between sexes, 2) characterize and quantify winter night roost habitat, and 3) identify spatial and temporal patterns of winter habitat use and behavior relative to temperature, wind speed, and ice-cover. Mean 95% fixed kernel estimate winter home range size was 6837 km2 (range 8 – 36 591) and was not significantly different between sexes. Upland habitat was used significantly more than floodplain habitat for winter night roosts for eight of the 13 individuals; whereas, floodplain was used in significantly greater abundance for two of the 13 individuals. Winter night roosts, sited in forest habitat, generally were located in areas dominated by cultivated crops; however, relative to the proportion of habitat availability within the home range of a particular individual, habitat types associated with the floodplain generally were used more frequently. Although these were the general trends, variation in winter night roost habitat use was evident among individuals and years. The results suggested proximity to water and isolation from human disturbance influenced winter night roost habitat selection. However, use of upland habitat suggested that other factors influence habitat selection. K-means cluster analysis identified three patterns of winter night roost habitat use: 1) use of areas dominated by cultivated crops with less deciduous forest (35.1% of locations), 2) use of deciduous forest with less cultivated crops (34.5% of locations), and 3) use of floodplain habitat (30.4% of locations). Likewise, K-means cluster analysis identified four behavioral patterns of winter night roost selection: 1) roost close to the river and to a lock and dam (67.5% of locations), 2) roost slightly south from a lock and dam but close to the river (23.5% of locations), 3) roost in an upland area relatively distant from the river, but no movement latitudinally (6.7% of locations), and 4) move south and roost in an upland area (2.3% of locations). The results of a discriminant function analysis using wind speed, temperature, and percent ice-cover as predictors of group membership detected no apparent patterns of winter night roost habitat use or behavioral patterns in response to wind speed, temperature, and ice-cover. Consequently, the high variability suggested that these factors alone or in combinations cannot account for the variation in macrohabitat use. Density-dependent competition for preferred food resources, dispersion because of other abiotic factors, or the level of habitat selection (e.g. microhabitat) might also be drivers of the variability in winter roosting behavior and habitat use. Further research into Bald Eagle winter night roosting behavior along the Upper Mississippi River corridor might help to elucidate possible patterns of habitat use that can guide future conservation efforts.