Population changes and their demographic drivers in landbirds of western North America: An assessment from the Monitoring Avian Productivity and Survivorship program

Abstract

We used capture–mark–recapture (CMR) models to estimate population trends (mean annual population change, λ̂ ) in western North America for 86 landbird species from 15 years (1992–2006) of data from the MAPS program (Monitoring Avian Productivity and Survivorship; www.birdpop.org/pages/maps.php). The mean λ̂ for 26 temperate-wintering migratory species that winter in the North Temperate Zone was significantly <1.0 (decreasing), nonsignificantly >1.0 (increasing) for 40 migratory species wintering in the neotropics, and nonsignificantly <1.0 for 20 permanent resident species. Values of λ̂ for the 86 individual species were positively correlated with the 1992–2006 trends for those species according to the Breeding Bird Survey (BBS), and the pattern of means of λ̂ from the two sources was similar for all three migration classes. For migratory species, we compared the 1992–2006 pattern of λ̂ from MAPS with the 1966–1991 and 1979–1991 population trends derived from BBS data. The result suggests that patterns of population change remained much the same from 1966 through 2006, but populations tended to decrease more during the most recent 15 years of those 4 decades. For four species selected as case studies, we used MAPS data to estimate apparent survival of adults and recruitment from CMR models, and to index adults’ population density, productivity, and post-breeding effects from generalized linear mixed models. For each of those four species we then examined temporal pairwise correlations among the annual estimates of λ̂ , population density of adults, apparent survival of adults, productivity, and postbreeding effects to make inferences regarding the proximate demographic drivers of population change. These correlations led us to hypothesize that the 1992–2006 population decreases for the Golden-crowned Kinglet (Regulus satrapa) were driven primarily by decreases in adult survival, for the Orange-crowned Warbler (Oreothlypis celata) by that and decreases in productivity. For the “Western” Flycatcher (Empidonax difficilis/occidentalis), however, we hypothesize that population decreases were driven primarily by first-year survival, as apparently were increases in the Warbling Vireo (Vireo gilvus) population. We suggest such population changes can be tested, and that the ultimate environmental drivers of population change for these and other species can be identified by integrated modeling of BBS, MAPS, and other demographic data in conjunction with local and landscape-scale data on habitat, weather, and climate.