Survival and movements of immature Bald Eagles fledged in northern California

We studied survival and movements of 13 radiotagged immature Bald Eagles (H aliaeetus leucocephalus) fledged in 1989 and 1990 from nests at Lake Britto n in northcentral California. Initial observations were consistent with a p reviously-described postfledgling northward migration into Canada and Alask a. First-year eagles returned to northern California between January and Ma y of the following year and moved extensively in the general region of nort hcentral California. Of the two cohorts, 10 birds were located within a yea r of fledging for a minimum first-year survivorship of 76.9%. Seven eagles returned to our study area. Five of these birds returned briefly to their n atal territories. Three of 10 returning birds were not observed again in ou r study area bur were recorded infrequently at distances of 50-190 km outsi de the study area. Two different movement patterns emerged within the 10 re turning birds: five birds showed a high degree of affinity to the study are a and five did not. In their second year of life, radiotagged immatures sho wed less affinity for our study area during late summer and fall. We could not determine if this disappearance indicated a regular or repeated migrati on, or merely an increased tendency to wander.