Imagine a harsh winter's night in 2021, where heavy snowstorms batter the United States. These extreme weather events are happening more frequently, potentially causing noticeable changes in wildlife. Meet the Eastern Bluebird (Sialia sialis), a small bird that might have undergone rapid natural selection due to these severe conditions. Scientists set out to determine if these snowstorms caused survival of the fittest among the bluebirds. They examined dead and surviving birds from three different sites, focusing on their body features and colors.

It seems that survival was tied to having longer legs (tarsus) and a more substantial beak—longer, wider, and deeper. This could be due to the starvation and thermal endurance factors. Interestingly, the more visually striking birds with vibrant plumage seemed less likely to survive. Perhaps these birds invested too much energy early on in mate selection or protecting their nesting sites.

As summers grow warmer, the longer limbs favored during these snowstorms might offer thermal advantages, continuing to be beneficial. However, the dull plumage that was favored during the cold spells might conflict with the benefits of more vivid colors during breeding season.

Extreme events like these snowstorms can't be easily predicted based on long-term climate change responses. What's more, the impacts of one event, like the 2021 snowstorms, might not mirror those of future extreme events.

Where Cold Winters Rule: How Bluebirds Adapt

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