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Owl Polymorphism

April 27, 2010

We have known that Eastern Screech Owls have two color morphs since at least 1874 when the famous Smithsonian ornithologist Robert Ridgway realized that both the rufous and gray owls were actually the same species. No other North American owl has such distinctive plumage forms.

Rufous and gray color morphs, called polymorphism, are found across the Eastern Screech-owl’s range, which extends from the southern prairies of Canada east to southern Maine and south to the Gulf of Mexico and Florida.

The ratio of rufous to gray morphs appears to fluctuate based on warm and wet (more rufous) to cold and dry (fewer rufous) climatic regions and cycles. In humid and warm regions like the mid-latitudes (Arkansas east to Georgia and, east of Appalachian Mts., north to coastal New York), 50 to 75 percent of the owls are rufous. On the western edge of their range were it is much drier, fewer than 15% are rufous. No rufous owls are known from San Antonio, Texas, to the Rio Grande Valley, although up to 8% of the screech-owls in central Texas are rufous. Rufous owls are rare in the northern portion of their range where it is cold.

Eastern Screech-owls can thrive in towns, suburbs and city parks. We tend trim and cut down dead and decaying trees with holes in them. These are just what screech-owls need for a nest or roost cavity. Hanging a nest box can help alleviate the lack of nest holes and allow you to enjoy a screech-owl in your neighborhood.

Once you purchase a nest box or find construction plans to make your own, the placement of the nest box is key. The box should be placed at least 10 feet high and in deep shade. Male screech-owls like to roost in dense tree foliage close to the nest during the day. Make sure you place the box away from paths or sidewalks. Screech-owls can be very aggressive when their young are about to fledge, sometimes swooping down on pedestrians passing by.

Make a prediction of which Eastern Screech-owl morph will occupy your nest box, then wait and watch.

One Comment leave one →
  1. April 29, 2010 6:13 pm

    Considering the amount of rain we’ve had in southern Florida this winter – can we expect extremely rufus Screech Owls?

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