Partitioning of Food and Niche Characteristics of Coexisting Accipiter During Breeding

Abstract

The abundance of resources and their use by Accipiter in two areas within Oregon from 1969 through 1974 are presented. In the coastal mountains of northwestern Oregon only Sharp-shinned Hawks (Accipiter striatus) and Cooper's Hawks (A. cooperii) nested. In the remainder of the state, A. striatus, A. cooperii, and Northern Goshawks (A. gentilis) were syntopic during the nesting season. The number of species and the total density of birds in eastern Oregon were about one-half those in northwestern Oregon. Mean prey size of A. striatus in northwestern Oregon (12.8 g) was significantly smaller than that of the same species in eastern Oregon (28.4 g). Accipiter striatus diets in both areas were composed almost entirely of birds (<5% mammals). Mean prey size of A. cooperii in both areas was nearly the same (134.7 g vs. 136.3 g) and was significantly larger than mean prey size of A. striatus. The frequency of occurrence and the size of prey taxa in A. cooperii diets, however, varied between areas: 74% birds (x̄ = 79.2 g) and 25% mammals (x̄ = 296.4 g) in northwestern Oregon versus 47% birds (x̄ = 123.7 g) and 53% mammals (x̄ = 147.5 g) in eastern Oregon. Mean prey size of A. gentilis in eastern Oregon (306.6 g) was significantly larger than that of A. cooperii and consisted of 55% birds (x̄ = 195.5 g) and 45% mammals (x̄ = 445.2 g). An analysis of prey sizes, prey taxa, and foraging heights indicated that, in general, food was partitioned in both areas primarily according to prey size. In eastern Oregon, however, where A. cooperii and A. gentilis overlapped broadly in prey size, these species tended to take different prey taxa. Both A. cooperii and A. gentilis foraged primarily in the lower zones (ground-shrub and shrub-canopy), whereas A. striatus foraged in the upper canopy.

Diet of Black-crowned Night-herons (Nycticorax nycticorax) in a Wetland of the Parana River´s Alluvial Valley

“…Besides, N. nycticorax mainly consumed bigger preys than B. striatus, A. albus (21-30mm for both species Beltzer 2007), and E. thula (11-20mm -Beltzer 2007). This reinforces the idea that prey size is more important than type in segregating similar syntopic species (Reynolds andMeslow 1984, Cooper et al 1990).…”

A Natural Hybridization of the Brown Goshawk Accipiter Fasciatus and Grey Goshawk Accipiter Novaehollandiae in Australia, and a Comparison of the Two Species

“…Novaehollandiae's short, wide, rounded, concave wing indicates that it makes relatively short, buoyant hunting (attack) flights, is more manouvrable at slow speeds, and spends less time on the wing than fusciatus; MacDonald (1973) describes its flight as owl-like. Habits of the various prey species EMU 85 taken, indicative of foraging zone (Reynolds & Meslow 1984), are generally consistent with these differences (Olsen & Olsen 1986).…”

Ecology of the Cooper's Hawk in North Florida

“…Several authors noted that Cooper's hawks focus on ground-and shrub-oriented prey (Reynolds and Meslow 1984;Bielefeldt et al 1992;Bosakowski et al 1992;Cava et al 2012). This was true in our study, because most of the avian taxa preferentially selected by Cooper's hawks primarily occur in these vegetation strata (Dickson and Noble 1978;Reynolds and Meslow 1984;Bielefeldt et al 1992;Bosakowski et al 1992).…”