Breeding bird survey (BBS) data are typically analyzed at the route level in which the average or combined total number of individuals across the 50 stops is treated as a single observation. However, analysis at the stop level may provide information on finer-scale habitat affiliations of species within the broader landscape, as well as changes in species distribution over time. Though once abundant, the Newfoundland Gray-cheeked Thrush (Catharus minimus minimus) underwent a dramatic population collapse across most of the island during the 1980s and 1990s and today is most common in montane forests. The reason for this collapse is not well understood but introduced North American red squirrels (Tamiasciurus hudsonicus), which colonized most forested areas on the island below ~400 m from the late 1970s through the mid-1990s, have been identified as a possible cause. To improve our understanding of changes in the elevational distribution of Gray-cheeked Thrushes, we compared stop-level BBS data from two periods. Our historic period from 1974-1984 corresponds with the initial expansion phase of introduced red squirrels, whereas that from 2000-2015 reflects a period during which the colonization of suitable habitat by squirrels was complete. We used 17 routes (850 stops) where the thrushes had been observed and there were at least 3 surveys completed during each period. Surveys during the 1970s and 1980s indicated that Gray-cheeked Thrushes were abundant at all elevations sampled by the BBS (0-450 m), with higher incidence below 100 m and above 300 m; in contrast, recent surveys indicate that the species is now essentially absent below 350 m. This finding highlights the value of historical stop-level BBS data for reconstructing changes in species distributions and is consistent with the hypothesis that red squirrels have adversely affected Newfoundland Gray-cheeked Thrushes.RESUMEN. Los datos de los muestreos de aves reproductoras (BBS, por sus siglas en inglés) suelen analizarse a nivel de ruta, en el que el número total medio o combinado de individuos a lo largo de las 50 paradas se trata como una única observación. Sin embargo, el análisis a nivel de parada puede proporcionar información sobre asociaciones de hábitat de las especies, a escala más fina dentro de un paisaje más amplio, así como cambios en la distribución de las especies a lo largo del tiempo. Aunque abundante en el pasado, el Zorzal de Cara Gris de Terranova (Catharus minimus minimus) sufrió un dramático colapso poblacional en la mayor parte de la isla durante las décadas de 1980 y 1990 y hoy es más común en los bosques montanos. La razón de este colapso no se conoce bien, pero la introducción de las ardillas rojas norteamericanas (Tamiasciurus hudsonicus), que colonizaron la mayoría de las zonas boscosas de la isla por debajo de ~400 m desde finales de los 70 hasta mediados de los 90, ha sido identificada como una posible causa. Para mejorar nuestra comprensión de los cambios en la distribución altitudinal de los Zorzales de Cara Gris, comparamos l...
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