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.