Bald eagle population increase, reproductive success, and nesting habitat in central interior California

Abstract

Over much of its range, the bald eagle (Haliaeetus leucocephalus) has substantially recovered from declines in the mid–late 1900s, which resulted from habitat loss, human persecution and disturbance, and contamination by the pesticide DDT. The species remains listed as endangered under the California Endangered Species Act (CESA). The species’ distribution, abundance, reproductive success, and habitat requirements have received little attention in recent years, perhaps because of a widespread belief that the bald eagle population is healthy in California. We evaluated the status of the bald eagle in the central part of interior California by conducting surveys, largely from publicly accessible roads near water bodies, and by accumulating records collected by others from 2011 through 2024. We estimate that the known bald eagle population in this region increased by annual average of 19% from four known nesting pairs in 2011 to 31 pairs in 2024. We documented 189 nesting attempts, of which 133 were adequately monitored over the whole nesting season. Seventy-seven percent of nesting attempts successfully fledged young, and productivity averaged 1.29 young/occupied nesting territory, both of which are consistent with a sustainable and increasing population. Eagles in this region constructed their nests in a variety of tree species, with the largest proportions in gray pine (Pinus sabiniana; 73%)and Fremont cottonwood (Populus fremontii; 15%), both of which were used infrequently as nest trees in California during the 1970s and 1980s. Nests were constructed at an average of 0.36 km from water bodies suitable for foraging, and most were away from roads and individual residences (x̄ > 1 km), denser development (x̄ > 4.0 km), and other potential sources of human disturbance (other than water-based recreational use). The population increase we documented, despite continued potential threats from climate-induced wildfire, human disturbance, electrocution, and lead and rodenticide poisoning, suggests a need for bald eagle surveys and status evaluations elsewhere in California to determine if delisting under CESA may be warranted.

Keywords

• bald eagle
• haliaeetus leucocephalus
• habitat
• population
• reproductive success
• status