Data from: Seasonal macro-demography of North American bird populations revealed through citizen science monitoring

Avian population sizes fluctuate and change over vast spatial scales, but the mechanistic underpinnings remain poorly understood. A key question is whether spatial and annual variation in avian population dynamics is driven primarily by variation in breeding season recruitment or by variation in overwinter survival. We present a method using large-scale eBird citizen-science data to develop species-specific indices of net population change as proxies for survival and recruitment gain, based on twice-annual, rangewide snapshots of relative abundance in spring and fall. We demonstrate the use of these indices by examining spatially explicit annual variation in survival and recruitment gain in two well-surveyed nonmigratory North American species, Carolina Wren (Thryothorus ludovicianus) and Northern Cardinal (Cardinalis cardinalis). We show that, while interannual variation in both survival and recruitment gain is slight for Northern Cardinal, eBird abundance data reveal strong and geographically coherent signals of interannual variation in the overwinter survival of Carolina Wren. As predicted, variation in wintertime survival dominates overall interannual population fluctuations of wrens and is correlated with winter temperature and snowfall in the northeastern United States, but not the southern United States. This study demonstrates the potential of volunteer-collected big datasets like eBird for inferring variation in demographic rates and introduces a new complementary approach towards illuminating the macrodemography of North American birds at comprehensive continental extents.