Does Survey Method Bias the Description of Northern Goshawk Nest-site Structure?

Abstmrr: Past str~dies on the nesting habitat of northern goshawks (Accipiter gentilis) often relied on nests fomid opportunistically, either during timber-sale operations, by searching apparently "good goshawk habitat, or 1)y other search methods where areas were preselected based on known forest conditions. Therefore, a bias in the characterimtion of habitat surrounding northern goshawk nest sites may exist toward late-forest structure (large trecs, high canopy closure). This potential problem has confo~~nded interpretation of data on nesting habitat of northern gosl~a\vks and added to uncertainty in the review process to consider the species for fcderal listing as threatened or endangcred. Systematic srtnley methods. which strive for complete coverage of an area and often llse broadcasts of conspecific calls, have been developed to overcome these potential biases, but no str~dy has compared habitat characteristics around nests foi~nd opport~~nistically with those found systematic~~llv. We compared habitat characteristics in a 0.4-ha area aror~nd nests found systematically (n = 27) versus those found opporti~nistically (11 = 22) on 3 national forests in eastern Oregon. \Ve found that both density of large trees (systematic: r = 16.4 + 3.1 trees/ha; r t SE; opportunistic: f = 21.3 2 3.2; P = 0.56) and canopy elosi~re (systematic: .t = 72 2 2%; opportunistic: .f = 70 + 2%; P = 0.61) \xlere similar around nests found wit11 either search method. Our results diminish concern that past survey methods mischaracterized northern goshawk nest-site s t~~ ic tu re . However, becar~se northern goshawks nest in a variety of forest cover types wit11 a \vide range of s t n ~ c t ~ ~ r a l characteristics. these results do not decrease the value of systematic sllnfey methods in determining the most representative habitat tlescriptions for northern gosha~vks. Rigoro~~s sulvey protocols allow repeatability and comparahility of monitoring efforts and results over time. JOURNAL OF WILDLIFE MANAGEMENT 62(4):137%1384