The response of Cooper's Hawks to experimental Ponderosa pine forest restoration treatments in an Adaptive Management Area

Graduation Date

2007

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Natural Resources: Wildlife, 2007

Committee Chair Name

T. Luke George

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Adaptive Management Area, Cooper's hawk, Prey abundance, Diet, Ponderosa pine, Humboldt State University -- Theses -- Wildlife, Foraging habitat selection

Abstract

I examined foraging habitat use, foraging site selection and diet of Cooper's Hawks within the Goosenest Adaptive Management Area in northern California, where experimental interior Ponderosa pine forest restoration treatments have been applied. Two different thinning treatments and a thinning and prescribed burning treatment were randomly applied to fifteen 40-ha units within the management area between 1998 and 2001. I radio-tagged and tracked nesting adults, and collected vegetation measurements at paired foraging and random locations during the 2005 and 2006 breeding seasons to assess foraging habitat selection at the stand-level and microhabitat spatial scales. In addition, I placed video systems on nests and used data collected on small mammal abundance in treatment and untreated control units to assess diet composition and prey abundance in foraging areas. I examined the prediction that Cooper's Hawks were selectively foraging in more open forest types both because these stands had higher abundances of preferred prey species and because their vegetation structure allowed for easier detection and acquisition of prey. Tagged hawks nested exclusively in dense, untreated stands, but selected more open forest types, including thinned and thinned/burned units and untreated matrix with open structure, for foraging. At the microsite scale, tagged hawks were selecting foraging sites with larger trees, higher tree densities, and lower canopy cover, though small differences between foraging and paired random locations across all vegetation variables collected indicated that selection among tagged hawks was occurring primarily at the stand level. Hawks delivered significantly more mammalian than avian prey to nests in both years, with golden-mantled ground squirrel (Spermophilus lateralis) and chipmunk species (Eutamius senex and E. amoenus) comprising over 98% of delivered mammalian prey in both years. Spermophilus lateralis and Eutamius amoenus abundance was significantly higher on thinned and thinned/burned treatment units than on untreated controls in both years. Thus, Cooper's Hawk preference for foraging in thinned and thinned/burned plots may be influenced by both vegetation structure and prey abundance. In addition, my results indicate that thinning and thinning/burning treatments aimed at restoring a more natural condition to interior Ponderosa pine forests can enhance foraging habitat for breeding Cooper's Hawks, but that dense, untreated stands must also be retained to provide suitable nesting habitat.

https://scholarworks.calstate.edu/concern/theses/bv73c307n

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