1. Introduction Continental population estimates of breeding landbirds (Rosenberg and Blancher 2005) were developed for the North American Landbird Conservation Plan (Rich et al. 2004) Uncertainty and low confidence in PIF estimates exists due to difficulties estimating their accuracy and precision and few efforts to validate them at different scales We compared PIF estimates to an intensive study by Hagan et al. (1997), who used a robust sampling framework to count birds in a 1,270 km 2 forested landscape in northern Maine Methods Hagan et al. (1997) estimates based on two visits to 387 point counts (50m fixed-radius) distributed across forest types and age-classes Data from six Breeding Bird Survey routes in the same landscape used to estimate densities and populations according to PIF methods (Rosenberg and Blancher 2005) To correct biases in both methods, BBS values were adjusted upwards to account for 3- versus 10-minute point counts for 15 species with published data (Buskirk & McDonald 1995) Hagan et al. (1997) values adjusted downward to account for overestimates of density in 50m fixed-radius point counts (Simons et al. 2007) Land cover around BBS routes was compared to habitat occurrence across the entire area Results Density and population estimates calculated by Hagan et al. (1997) were higher than PIF estimates for 94% of species (n=70) Median density and population estimates by Hagan et al. were >9 times higher than corresponding PIF values The mean ratio of Hagan : PIF populations was >25 (density ratio = 21) Hagan’s estimates were >10 times higher than PIF estimates for 44% of species; For 10% of species, Hagan’s estimates were >50 times higher than PIF values Hagan’s mean (median) population estimate was 20,110 (10,527) birds; the PIF mean (median) was 2,272 (971) birds BBS routes sampled habitat types in rough proportion to their occurrence in the study landscape Discussion Hagan and PIF estimates differed by an order of magnitude for half the species examined and differed most for a suite of boreal ( Three-toed Woodpecker, Yellow-bellied Flycatcher, Boreal Chickadee, Gray Jay, Blackpoll Warbler, Lincoln’s Sparrow ) and sub-boreal bird species ( Blackburnian & Canada Warbler ). For that group Hagan’s estimates were typically 100 times higher than PIF estimates. Most of that group are PIF species of continental importance. Given the robust sampling framework and greater sampling intensity, Hagan’s estimates are presumably more accurate than PIF estimates for this landscape. Biased sampling of habitat types did not appear to drive o bserved differences, which were most likely due to: 1)Higher detection rates by Hagan et al. (10-min counts, two visits) 2)Probable overestimates of abundances in 50m- radius circles by Hagan et al. With preliminary correction methods applied, Hagan estimates were typically three times higher than PIF estimates for most species. Randy Dettmers 1, Mitch Hartley 1, and Tom Hodgman 2 1 U.S. Fish & Wildlife Service, Hadley, MA and 2 Maine Dept. Inland Fisheries & Wildlife, Bangor, ME Literature Cited Buskirk, W.B. and J.L. McDonald. 1995. Comparison of point count sampling regimes for monitoring forest birds. Pages 25-34 in USDA Forest Service PSW-GTR-149. Albany, CA. Hagan, J.M, P.S. McKinley, A.L. Meehan, and S.L. Grove. 1997. Diversity and abundance of landbirds in a northeastern industrial forest. J. Wildl. Manage. 61:718-735. Rich, T.D., C.J. Beardmore, H. Berlanga, P.J. Blancher, M.S.W. Bradstreet, G.S. Butcher, D.W. Demarest, E.H. Dunn, W.C. Hunter, E.E. Iñigo-Elias, J.A. Kennedy, A.M. Martell, A.O. Panjabi, D.N. Pashley, K.V. Rosenberg, C.M. Rustay, J.S. Wendt, and T.C. Will. 2004. Partners in Flight North American Landbird Conservation Plan. Cornell Lab of Ornithology. Ithaca, NY. Rosenberg, K.V. and P.J. Blancher. 2005. Setting numerical population objectives for priority landbird species. Pages 57- 67 in Proceedings of the Third International Partners in Flight Conference 2002. Volume 1. USDA Forest Service PSW-GTR-191. Albany, CA. Simons, T.R., M.W. Alldredge, K.H. Pollock, and J.W. Wettroth. 2007. Experimental analysis of the auditory detection process on avian point counts. Auk 124:986-999. For Further Information Contact randy_dettmers@fws.gov or mitch_hartley@fws.govrandy_dettmers@fws.govmitch_hartley@fws.gov This poster can be obtained at www.acjv.org/pif_poster.htm Figure 1. Ratio of Hagan et al. (1997) : PIF population estimates. Bars represent number of species in each category. Figure 2. Hagan and PIF density (birds/50 ha) estimates as calculated and adjusted for likely biases. An assessment of PIF population estimates for forest birds in Northern Maine Correction Factors Ratios of adjusted Hagan:PIF densities were 32% of original ratios (4:1 to 1.4:1 median). However, most species in this analysis (eastern deciduous birds) were quite uncommon in the study area. Conclusions Though PIF population estimates are largely untested and imprecise, they have been used to set population and/or habitat objectives at continental and regional scales. Such objectives will be more meaningful if we can better understand the accuracy of these estimates.