Osprey and Bald Eagle populations suffered long-term decline and range contraction in California from persecution, habitat loss, and pesticides. Both species are believed to have recovered, but recent changes in geographic range, populations, reproductive success, and habitat use remain mostly unstudied. We studied both species within the central portion of the Central Valley and Sierra foothills. Osprey colonization began in the 1970s, and during 2020-2024, the nesting population increased at only 4.3% annually, suggesting near habitat saturation. Over recent years, 73% of 181 Osprey nest attempts were successful, producing an average of 1.32 young per occupied nest, indicating a healthy population. Osprey nests were mostly placed on artificial structures (91%), mainly utility poles (58%). Over 2011-2024, breeding Bald Eagles increased by 18% annually, from 4 to 31 pairs. Reproductive success was healthy, with 79% of 133 nests successful and 1.29 young fledged per occupied nest. Eagles mostly nested in gray pines, Fremont cottonwoods, and other species near major waterbodies. These two species’ increases have likely resulted from reduced persecution, reservoir construction, nest protection, and contaminant declines. Competition from the increasing Bald Eagle population may reduce Osprey numbers, but habitat selection differences will likely maintain healthy populations of both species.

Daniel Airola is a certified Wildlife Biologist who has practiced in northern California for 45 years. He has worked for land management agencies, environmental consulting firms, and and an independent researcher. He first worked on Bald Eagles and Ospreys in the early 1980s, shortly after DDT was banned in the U.S. He has published over 90 studies consisting mostly of quantified natural history and community science-based research addressing population status, reproductive success, habitat requirements, and migration patterns at-risk birds, including the Purple Martin, Tricolored Blackbird, Yellow-billed Magpie, Swainson's Hawk, Turkey Vulture, box-nesting and migratory songbirds, and wintering diving ducks.