How well do regional or national Breeding Bird Survey data predict songbird population trends at an intact boreal site?

A study to monitor boreal songbird trends was initiated in 1998 in a relatively undisturbed and remote part of the boreal forest in the Northwest Territories, Canada. Eight years of point count data were collected over the 14 years of the study, 1998-2011. Trends were estimated for 50 bird species using generalized linear mixed-effects models, with random effects to account for temporal (repeat sampling within years) and spatial (stations within stands) autocorrelation and variability associated with multiple observers. We tested whether regional and national Breeding Bird Survey (BBS) trends could, on average, predict trends in our study area. Significant increases in our study area outnumbered decreases by 12 species to 6, an opposite pattern compared to Alberta (6 versus 15, respectively) and Canada (9 versus 20). Twenty-two species with relatively precise trend estimates (precision to detect > 30% decline in 10 years; observed SE < 3.7%/year) showed nonsignificant trends, similar to Alberta (24) and Canada (20). Precision-weighted trends for a sample of 19 species with both reliable trends at our site and small portions of their range covered by BBS in Canada were, on average, more negative for Alberta (1.34% per year lower) and for Canada (1.15% per year lower) relative to Fort Liard, though 95% credible intervals still contained zero. We suggest that part of the differences could be attributable to local resource pulses (insect outbreak). However, we also suggest that the tendency for BBS route coverage to disproportionately sample more southerly, developed areas in the boreal forest could result in BBS trends that are not representative of range-wide trends for species whose range is centred farther north.Original Abstract: Une etude visant a suivre la tendance de passereaux boreaux a ete amorcee en 1998 dans une partie relativement peu perturbee et isolee de la foret boreale des Territoires du Nord-Ouest, au Canada. Nous avons echantillonne des points d'ecoute pendant 8 des 14 annees qu'a dure l'etude (1998-2011). La tendance a ete estimee pour 50 especes d'oiseaux au moyen de modeles lineaires generalises a effets mixtes, pour lesquels les effets aleatoires ont tenu compte de l'autocorrelation et de la variabilite temporelles (repetabilite intra-annuelle) et spatiales (stations a l'interieur des peuplements) associees aux observateurs multiples. Nous avons teste si les tendances regionales et nationales du Releve des oiseaux nicheurs (BBS) pouvaie