>>51878755Anthropogenic climate change is altering the seasonality of climate and driving changes
in the seasonal timing of biological events of many species. The magnitude of such
phenological changes can vary greatly among species, particularly if they respond
to different environmental cues when making reproductive decisions. Phenological
mismatch occurs when asymmetric phenological responses to climate change cause
important species interactions to become asynchronous. Secondary consumers, such
as birds, may be particularly vulnerable to such mismatch because they can respond
to changing climatic cues differently than their food sources. Migratory birds are
expected to face additional risk due to their limited ability to respond to the local
climate conditions of their breeding grounds while they are in their wintering range. To
determine the extent to which phenological mismatch is causing population changes in
more than 1,000 north temperate birds, I generated a north temperate map of potential
mismatch based on temporal changes in heat accumulation. Using ordinal regression
analysis, I tested for a correlation between the degree of mismatch within each species’
range and its conservation concern. I found that non-migratory species experiencing the
severest degree of mismatch tended to show positive population growth and be of least
conservation concern while migratory species experiencing severe mismatch tended to
show negative population growth and be of greatest conservation concern. These results
may be explained by the greater potential for resident species to adjust their breeding to
an earlier spring, allowing residents a longer breeding season overall. Migrants may be
unable to advance their phenology to match that of their breeding grounds, leading to
disrupted species interactions and population declines. Understanding the complexity of
the consequences of phenological mismatch on both resident and migratory birds will
be important for informing and directing efforts to conserve these species in the future.
