Building a better baseline to estimate 160 years of avian population change and create historically informed conservation targets

Globally, anthropogenic land‐cover change has been dramatic over the last few centuries and is frequently invoked as a major cause of wildlife population declines. Baseline data currently used to assess population trends, however, began well after major changes to the landscape. In the United States and Canada, breeding bird population trends are assessed by the North American Breeding Bird Survey, which began in the 1960s. Estimates of distribution and abundance prior to major habitat alteration would add historical perspective to contemporary trends and allow for historically based conservation targets. We used a hindcasting framework to estimate change in distribution and abundance of 7 bird species in the Willamette Valley, Oregon (United States). After reconciling classification schemes of current and 1850s reconstructed land cover, we used multiscale species distribution models and hierarchical distance sampling models to predict spatially explicit densities in the modern and historical landscapes. We estimated that since the 1850s, White‐breasted Nuthatch (Sitta carolinensis) and Western Meadowlark (Sturnella neglecta) populations, 2 species sensitive to fragmentation of oak woodlands and grasslands, declined by 93% and 97%, respectively. Five other species we estimated nearly stable or increasing populations, despite steep regional declines since the 1960s. Based on these estimates, we developed historically based conservation targets for amount of habitat, population, and density for each species. Hindcasted reconstructions provide historical perspective for assessing contemporary trends and allow for historically based conservation targets that can inform current management. Construcción de una Mejor Línea Base para Estimar 160 Años de Cambio en la Población de Aves y Crear Objetivos de Conservación Orientados Históricamente Resumen A nivel mundial, el cambio antropogénico en la cobertura del suelo ha sido dramático durante los últimos siglos y frecuentemente se le considera una de las principales causas de las declinaciones en la población de fauna. A pesar de esto, se comenzó a registrar los datos de línea base que se usan actualmente para evaluar las tendencias poblacionales mucho después de cambios importantes en el paisaje. En los Estados Unidos de América y en Canadá, las tendencias poblacionales de las aves reproductoras se evalúan por medio del Censo de Aves Reproductoras, el cual comenzó en la década de 1960. Los estimados de la distribu