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Saturday, April 11, 2015

Is my owl a male or female??

Frederick R. Gehlbach studied screech owls in Texas from 1967 until 1991.  His focus was on population studies and his extensive observations were published in The Eastern Screech Owl, Life History, Ecology, and Behavior in the Suburbs and Countryside.  (NOTE:  Thanks for Jim Wright for providing me a copy of this seminal work in this field).  While this work contains a substantial amount of data (almost too much to comprehend), it is difficult for most of us to use to interpret our own nest boxes in a couple of important ways:

1)  He routinely netted (including owls roosting in trees) and/or captured the owls from boxes.  This was important for the scientific data he was seeking but most of us don't, or at least shouldn't be, intruding on their lives to that extent.  This allowed him to do determine the sex of each owl and follow individuals (he banded them), not only through a season, but from year to year.
2)  His results provide detailed statistical information on large populations but never really focus down to an individual bird or pair of birds.
3)  Since it was his career, he spent more time (day and night) than even I do!

I have been watching the Screech Owls in my yard for more than 10 years now, the last 5 with a nature cam in the nest box (an advantage that Gehlbach didn't have).  So what can I share with those of you who have contacted me about your nest boxes?

Background;  My box is located about 50 feet from my back door in a suburban yard.  Immediate neighbors have lots of a little over an acre; across a major street is a development of about 1/2 acre lots.  Except for mine, most lack a diversity of wildlife habitat, mostly standard lawns with a few shrubs and isolated trees.  Behind my lot however is a farm field (cows), an "old" field undergoing succession to mostly invasive species, and eventually a major river with mature trees.

Here are a couple of observations:
1)  When a female has been in the box with eggs and/or young, she virtually NEVER looks out of the box from dawn until it is too dark for us humans to see well. The only way I know she is there without the camera is when another bird (chickadee, titmouse, or bluebird most often) looks into the box and announces to the world that it is occupied!
2)  Prior to egg laying, owls are occasionally seen looking out of the box during the day, sometimes for long periods--with their eyes closed (but very much aware of their surrounding).  This may be a function in my yard of the proximity of my bird feeding station with birds (like blue jays that will mob an awake owl.
3)  This was the first year that a roosting owl spent as much time as it did (sometimes several hours a day, and virtually everyday for at least 1/2 hour before sunset) looking out.
4)  This was also the first year that an owl roosted nearly every day from mid-February until mid-March in the box; in past years you could count the days on one hand.

So, if you see an owl in your box, it is likely NOT a nesting female.  But is it a male, or a pre-nesting female??

From Gehlback, "Males inside or close to cavities by late February, replaced by their mates in mid-March, are strong evidence of nesting, so I often find the first egg within a day of laying."

(ponder that and I will provide more tomorrow . . .)

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