Data from: Natural selection after severe winter favors larger and duller bluebirds

Extreme cold events, which have become more frequent, can revert the
direction of long-term responses to climate change. In 2021, record
snowstorms swept the United States, causing wildlife die-offs that may
have been associated with rapid natural selection. Our objective was to
determine if the snowstorms caused natural selection in Eastern Bluebirds
(Sialia sialis). To test which mechanism most influenced their survival,
we measured the morphology and coloration of fatalities and survivors at
three sites. Survival was associated with a longer tarsus, and a wider,
longer, and deeper beak in support of the starvation and thermal endurance
hypotheses. Additionally, bluebirds with more-ornamented plumage were less
likely to have survived, maybe because of an early energy investment in
mate and site acquisition. As bluebirds encounter increasingly warm summer
conditions, the longer extremities favored during the snowstorms may
continue to be favored through their thermoregulatory benefits. However,
the dull plumage coloration favored by natural selection during the
snowstorms may be opposed by sexual selection benefits of more-ornamented
plumage. Overall, responses to extreme events are difficult to predict
from responses to long-term climate change, and responses to one event
such as the 2021 snowstorms may not predict responses to a future extreme
event.