Golden Eagles Nesting in an Urban Setting in a Canary Island Date Palm Tree, San Jose, California

Golden Eagles (Aquila chrysaetos) are uncommon residents in the densely populated south San Francisco Bay area, California, USA, especially within the city of San Jose (Bousman 2007). Nesting Golden Eagles have not been reported within the city limits since 1892 (Barlow 1893, California Department of Fish and Wildlife 2021). Contributing factors for this absence might include limited foraging and nesting habitat. Golden Eagles typically nest on cliffs and tall trees (Katzner et al. 2020) such as pine trees (Pinus spp.), oaks (Quercus spp.), and eucalyptus (Eucalyptus spp.; Bousman 2007). Regionally, they nest in remote areas at higher elevations in the adjacent ranges and foothills to the east and west of San Jose. Here we describe our observations of Golden Eagles nesting in a Canary Island date palm tree (Phoenix canariensis) on the valley floor in approximately 202 ha of open grasslands adjacent to the San Jose–Santa Clara Regional Wastewater Facility (RWF) within the city of San Jose (37.42469468N, 121.95074798W). A pair has nested in the same stand of trees there for five consecutive years, 2018–2022. The RWF is located north of Highway 237 and south of the Don Edwards National Wildlife Refuge at the southern end of the San Francisco Bay. The ridgeline of the Diablo Range is approximately 10 km to the east and the Santa Cruz Mountains ridge is approximately 24 km to the west of the site. The ruderal grassland adjacent to the RWF formerly provided a safety zone (hereafter, bufferlands) between the RWF and surrounding residential areas when large quantities of chlorine were stored at the facility as part of its normal operations. At present, the bufferlands provide foraging and nesting habitat for several raptor species including White-tailed Kites (Elanus leucurus), American Kestrels (Falco sparverius), and Burrowing Owls (Athene cunicularia). Since 2013, we have conducted yearround monthly surveys for Burrowing Owls at this location. We conducted surveys during a 4–5 hr time-period, and we performed other tasks during additional opportunistic site visits during the peak of the Burrowing Owl breeding season (April–August). During these surveys, we occasionally observed a single Golden Eagle foraging, usually during fall and winter. However, starting November 2017, we regularly observed a pair of Golden Eagles hunting for California ground squirrels (Otospermophilus beecheyi) and roosting in a small stand of Canary Island date palm trees located in the center of the site at an elevation of approximately 10 m above mean sea level. We confirmed a large nest among the fronds of the biggest palm tree (diameter at breast height: 108 cm) in May 2018. The nest was approximately 10 m above ground on the northeast side of the tree. We inspected the nest structure using binoculars and examined nest material we found on the ground in January 2021 after a high-wind event. The nest was constructed primarily of eucalyptus branches, most likely from two trees located immediately adjacent to the palm trees. Other nest material included palm fronds and mustard (Brassica spp.) stalks. Among the fallen nest material, we detected approximately 31 carcasses of California ground squirrels, a common prey item for Golden Eagles (Wiens et al. 2018, Brown et al. 2021). We found no prey remains of any other species. To the best of our knowledge, this is the first record of a Golden Eagle nest in a palm tree in an urban setting. The closest development to the nest was the RWF facility 366 m to the northeast. Office complexes lined the fenceline 394 m to the southwest, and a highway bordered the bufferlands to the south, 578 m from the nest. Breeding Golden Eagles rarely range farther than 3 km from their territory centers (Watson et al. 2014). Most of the area within 3.2 km of the nest is densely developed land containing two major freeways, commercial and residential development, a landfill, and a recycling center. The Santa Cruz Predatory Bird Research Group (1999) studied a population of Golden Eagles in the Altamont Pass east of Livermore, California (approximately 65 km northeast of the RWF) and found that all but a few pairs 1 Email address: philip.higgins@talonecological.org