Boise State University Master of Science in Raptor Biology student Kevin Myers defended his thesis, “Developmental and Ecological Factors Associated with the Post-Fledging Dependence Period in a Long-Lived Raptor” on the afternoon of February 27, 2026. Myers’s main advisor is Julie Heath (Boise State University Raptor Research Center Director, Biological Sciences, MS Raptor Biology ’96), and his committee also includes Jen Cruz (Boise State University Raptor Research Center, Biological Sciences) and Joe Eisaguirre (U.S.G.S. Research Wildlife Biologist – Alaskan Science Center Ecosystem Analytics team and Boise State adjunct graduate faculty member).
ABSTRACT
The post-fledging dependence period (PFDP) marks the transition from parental care to independence as young raptors acquire flight and hunting skills vital for survival. Unlike other developmental stages, PFDP duration can vary widely within species, likely reflecting individual heterogeneity in development, endogenous or environmental cues associated with dispersal or migration timing, or both. We investigated how developmental factors (diet breadth and sex) and cues associated with large-scale movements (physiological condition, hatch date, and time of year) influence PFDP duration in golden eagles (Aquila chrysaetos) in southwestern Idaho, USA. We predicted that PFDP duration would be positively associated with diet breadth and longer for females than males because female eagles are larger than males. We predicted a negative association between PFDP length and fledging condition, with PFDPs ending in the fall as decreasing day lengths and inclement weather becomes more frequent. Finally, we assessed whether PFDP length explained first-year survival. We used motion-activated cameras to record diet and fledging date, measured hematocrit and mass when nestlings were 7-8 weeks old to represent condition, and genetically determined sex from blood samples. We fit young eagles with transmitters and followed movement from fledging to dispersal to calculate the PFDP length. PFDP length ranged from 60 to 240 days, highlighting substantial intraspecific variation in the timing of independence among juvenile eagles. There was a positive association between diet breadth and PFDP (ß = 0.34 ± 0.10), supporting the hypothesis that fledglings from diet generalist parents require extended learning periods to acquire diverse hunting strategies. Contrary to our predictions, male fledglings had 49% longer PFDPs than females (ß = 0.40 ± 0.15). Eagles with higher hematocrit (better condition) had shorter PFDPs compared to eagles with lower hematocrit (ß = -0.26 ± 0.10). Most (57%) PFDPs ended when birds dispersed between 5 Sep. and 19 Oct. Finally, we found a non-significant, positive trend between PFDP length and survival through the first year. For golden eagles, developmental milestones such as learning to hunt effectively and cues associated with dispersal or migration, such as physiological condition and time of year, are key determinants of PFDP length. Prolonged PFDP durations may benefit young eagles, but the carry-over costs of prolonged care on adults remain unknown.