Background: Did you know that some animals have evolved to look a particular way in order to blend into their surroundings? Maybe you’ve seen the snowshoe hare – a rabbit that is white in winter and brown in summer, for camouflage. Some owls live in places that get a lot of snow, and it’s better if they evolve to be light colored rather than brown, so they can survive and blend in during the tough winter season.

This graph shows results from a recent study in Finland that claims to be the first one to see long-term changes in the color of a population (a large group) of owls, linked to changing snow conditions. The researchers claim that fewer white owls survive, and more brown owls survive, when winters have less snow.

Here are the details: In the graph, survival (on the Y axis) can be thought of like a percent – so 0.8 is like 80% of owls surviving. Survival of the owls is plotted in relation to snow depth. Grey owls are denoted by grey circles and brown ones by red diamonds. Each symbol represents the average survival of a sampled group of owls and the error bars are standard errors of the estimated survival within each group. The lines are regression slopes based on the data.

Data Source: Karrell et al. 2001, Nature Communications, doi:10.1038/ncomms1213. Available: