DOES SURVEY METHOD BIAS THE DESCRIPTION OF NORTHERN GOSHAWK NEST-SITESTRUCTURE

Past studies on the nesting habitat of northern goshawks (Accipiter ge ntilis) often relied on nests found opportunistically, either during t imber-sale operations, by searching apparently ''good'' goshawk habita t, or by other search methods where areas were preselected based on kn own forest conditions. Therefore, a bias in the characterization of ha bitat surrounding northern goshawk nest sites may exist toward late-fo rest structure (large trees, high canopy closure). This potential prob lem has confounded interpretation of data on nesting habitat of northe rn goshawks and added to uncertainty in the review process to consider the species for federal listing as threatened or endangered. Systemat ic survey methods, which strive for complete coverage of an area and o ften use broadcasts of conspecific calls, have been developed to overc ome these potential biases, but no study has compared habitat characte ristics around nests found opportunistically with those found systemat ically. We compared habitat characteristics in a 0.4-ha area around ne sts found systematically (n = 27) versus those found opportunistically (n = 22) on 3 national forests in eastern Oregon. We found that both density of large trees (systematic: (x) over bar = 16.4 +/- 3.1 trees/ ha; (x) over bar +/- SE; opportunistic: (x) over bar = 21.3 +/- 3.2; P = 0.56) and canopy closure (systematic: (x) over bar = 72 +/- 2%; opp ortunistic: (x) over bar = 70 +/- 2%; P = 0.61) were similar around ne sts found with either search method. Our results diminish concern that past survey methods mischaracterized northern goshawk nest-site struc ture. However, because northern goshawks nest in a variety of forest c over types with a nide range of structural characteristics, these resu lts do not decrease the value of systematic survey methods in determin ing the most representative habitat descriptions for northern goshawks . Rigorous survey protocols allow repeatability and comparability of m onitoring efforts and results over time.