A critical element of diet analysis is species adaptability to alternative prey sources. The breeding season diet of Northern Goshawks (Accipiter gentilis) includes both mammalian and avian species, varies geographically, and is often dependent upon tree squirrels of the genera Sciurus and Tamiasciurus>/i>. We studied alternative prey sources of Northern Goshawks in the South Hills of south-central Idaho, an area where tree squirrels are naturally absent and other prey frequently important in the diet of goshawks, such as smaller corvids, are uncommon. We quantified the diet of goshawks using nest cameras and surveyed abundance of prey using line transects. We found that goshawks consumed roughly 18.5% birds and 78.7% mammals by biomass, dominated specifically by the Belding’s ground squirrel (Urocitellus beldingi, also known as Spermophilus beldingi; 74.8% of total biomass consumed), but the percentage of diet varied between years. This diet was low in diversity, with high overlap among nests indicating a strong local dependence on the dominant food item. Lastly, larger broods consumed a greater proportion of mammalian prey than smaller broods. This study provides new insight into the adaptability of the goshawk, particularly in areas with unique prey assemblages.