Demographic consequences of phenological asynchrony for North American songbirds

Changes in phenology in response to ongoing climate change have been
observed in numerous taxa around the world. Differing rates of
phenological shifts across trophic levels have led to concerns that
ecological interactions may become increasingly decoupled in time, with
potential negative consequences for populations. Despite widespread
evidence of phenological change and a broad body of supporting theory,
large-scale multi-taxa evidence for demographic consequences of
phenological asynchrony remains elusive. Using data from a
continental-scale bird banding program, we assess the impact of
phenological dynamics on avian breeding productivity in 41 species of
migratory and resident North American birds breeding in and around
forested areas. We find strong evidence for a phenological optimum where
breeding productivity decreases in years with both particularly early or
late phenology and when breeding occurs early or late relative to local
vegetation phenology. Moreover, we demonstrate that landbird breeding
phenology did not keep pace with shifts in the timing of vegetation
green-up over a recent 18-year period, even though avian breeding
phenology has tracked green-up with greater sensitivity than arrival for
migratory species. Species whose breeding phenology more closely tracked
green-up tend to migrate shorter distances (or are resident over the
entire year) and breed earlier in the season. These results showcase the
broadest-scale evidence yet of the demographic impacts of phenological
change. Future climate change-associated phenological shifts will likely
result in a decrease in breeding productivity for most species, given that
bird breeding phenology is failing to keep pace with climate change.