Breeding Ecology of The Northern Goshawk ( Accipiter Gentilis ) within a Unique Prey and Forest Landscape of the Western United States

• Main Author: Miller, Robert Arnold
• Format: Text
• Language: unknown
• Published: ScholarWorks 2013
• Subjects: Diet; Prey abundance; Habitat Selection; Occupancy; Population Biology; Accipiter gentilis; Northern Goshawk
• Online Access: https://scholarworks.boisestate.edu/td/375; https://scholarworks.boisestate.edu/context/td/article/1378/viewcontent/auto_convert.pdf

The high-elevation mixed aspen-lodgepole pine and shrub-steppe landscapes of the northern Great Basin in the western United States provide unique challenges for a forest predator such as the Northern Goshawk (Accipiter gentilis). The forests naturally lack common goshawk prey species such as tree squirrels of the genera Sciurus and Tamiasciurus, and other preferred prey species such as corvids are uncommon. The forest structure is highly fragmented and makes up only about 20% of the shrub-steppe dominated landscape limiting cover, nesting locations, and other forest aspects preferred by goshawks. I studied many aspects of the breeding ecology of goshawks in the area including the breeding season diet, nest stand attributes, and the influence of prey abundance, nest stand structure, and territory structure on nest occupancy and productivity. A critical element of diet analysis is species adaptability to alternative prey sources. The breeding season diet of goshawks includes both mammalian and avian species, varies geographically, and is often dependent upon tree squirrels of the genera Sciurus and Tamiasciurus. I quantified the diet of goshawks using nest cameras and surveyed abundance of prey using line transects. I found that goshawks consumed roughly 18.5% birds and 78.7% mammals by biomass, dominated specifically by the Belding’s ground squirrel (Spermophilus beldingi; 74.8% of total biomass consumed). This diet was low in diversity with high overlap among nests indicating a strong local dependence on this specific diet. Higher avian prey abundance early in the nesting season seemed to drive an increased consumption of mammalian prey later in the nesting season. The availability of mammalian prey during the egg-laying phase of the breeding season was limited by hibernation. In turn, consumption of avian prey early in the nesting cycle likely influenced brood sizes. Larger brood sizes increased the demand for prey biomass later in the nesting season, resulting in a switch to heavier mammalian prey. This study ...