Sunday, March 3, 2013

Eastern Screech-Owl

A friend directed Erika and me to this gray-phase Eastern Screech-Owl in Minneapolis. In the field, we thought this owl kept its eyes tight shut, but, looking at this photograph, this bird did keep almost half-an-eye on us. Notice that the owl’s right eye is open by a slit—you can barely see its greenish-yellow eye and its black pupil.

Eastern Screech-Owls come in gray and rufous morphs. Northern birds are more often gray, while more southern birds are often rufous. Both phases can hatch out of the same nest. Although the situation may be more complex, the rufous plumage appears to be due to a dominant gene, and gray is recessive. Apparently rufous feathers are not as robust as gray ones, so the rufous birds may have less insulation in cold climates. Females are more often rufous than males. Females tend to be larger than males, and, because of the resultant relatively low surface area to body mass ratio, retain heat better than males. Finally, urban populations contain more rufous individuals than do surrounding rural areas. Cities often create heat traps during cold winters—allowing urban rufous birds to survive (Gehlbach 1995).

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