Among tawny owls in Finland, gray feathers have traditionally been more popular than brown. This genetically defined trait, however, is shifting its balance. Each year, more brown owls are counted, as the number of gray owls declines.
The reason for this shift, new research suggests, is the gradual warming of winters brought on by climate change.
It is thought that because brown owls are more visible to predators during times of heavy snow, they have, in the past, had a harder time surviving into the breeding season. As winters have warmed, and heavy snowfall has become less common, the brown owls have been better able to blend in with their environment.
The shift, research has shown, is not insignificant. Brown tawny owls, now make up 50 percent of the total population, an increase of 20 percent from previous estimates. At the current rate, researchers predict gray tawny owls may disappear completely.
Patrik Karell, the researcher from the University of Helsinki who authored the study, explained:
Its survival has improved as winters have become warmer...in other words, climate-driven selection has led to an evolutionary change in the population.
The loss of the gray owls would represent a major reduction in the specie's gene pool, making it more vulnerable to environmental changes in the future. Furthermore, previous research has suggested that brown tawny owls have other genetic disadvantages like weaker immune systems and higher metabolic rates.
More generally, the shift in the tawny owl population shows that climate change can lead to a reduction in genetic variability within species—even at the detriment to traits that once favored survival.