Rufous vs Gray
From the Peterson Field Guide.
The Eastern Screech Owl is a species that have two distinct morphs and live within the same population (polymorphism). It is generally known that gray-morphed Screech Owls are more frequently found in the North and the rufous-morphed birds are mostly found in the South. Many publications will discuss this relationship with the rufous-morphed birds not being able to handle the colder winters and I know there are some studies are trying to prove that. I did find an interesting publication by Mosher and Henny (1976) who explains how the rufous-morphed Screech Owls oxygen uptake is greater than the gray-morphed birds when exposed to lower temperatures. I have also heard about the relationship with the different morphs and tree species that are found in the areas !! (more…)