A test of niche centrality as a determinant of population trends and conservation status in threatened and endangered North American birds

Abundance and other aspects of population ecology have long been known to contribute to shaping the geography of species' distributions. In particular, abundance patterns have recently been shown to negatively correlate with environmental distance from conditions in the center of a species' abiotic niche, rather than vary with distance from the geographic center of a species' distribution. We tested for such associations across 8 species of endangered or threatened bird species in North America using population trend data derived from > 4 decades of North American Breeding Bird Surveys. Although we found no consistent overall pattern, we did observe negative population trends at conditions that were the most extreme within species' niches. This suggests that niche peripherality is a relevant factor to consider in conservation planning. Specifically, environmentally peripheral sites may be poor places in which to protect populations of endangered and threatened species, irrespective of how centrally they may occur within species' geographic distributions.