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Subject:

Screech Owl Development, some answers

From:

Sue Hamilton

Reply-To:

Sue Hamilton

Date:

Tue, 16 Jun 2009 06:50:33 -0700

My ornithology course (back in the 60's) taught that birds of prey-- and many other species-- start incubating with the laying of the first egg.  (Subsequent eggs may be laid one or more days apart.)  We were taught that this is a mechanism allowing survival of fewer young during years of food shortage, and survival of more during years of plenty.  
 
This is why I puzzled over the differences in the owlets in my back yard: the first two fledged within an hour of each other, and the third four days later. 
 
The truth is almost always more complicated than the original teachings. 
 
Sherman Suter has provided the reference which explains the pattern. (The Birds of North America series no. 165, 1995 by Frank Gehlbach)  (He) "claims that 63% of  females begin brooding with the first egg, 25% with the second, and the remainder with the third."
 
Aha!  Obviously my resident female screech owl started brooding with the second egg.
 
The third owlet fledged Sunday evening while my grandchildren watched-- he fluttered to the ground, hopping wildly about among the undergrowth, until my son went down,   picked him up, and put him on a high branch. All this took place while the adults watched from nearby branches.  A few minutes later the owlet was gone.  I hope he used his climbing ability to good advantage.  His older siblings climbed up a tree trunk, fluttered down to another, and then climbed up again, successfully moving toward the waiting adults who kept up a continual tremulo. 
 
We still hear tremulous hooting and have spotted the adults at the edge of a nearby bamboo thicket, but are staying away from the family as the crows are watching everything, and we don't want to add to the traumas.
 
We are, however, suffering from withdrawal symptoms, and frequently stare at the empty nestbox.
 
This is our fourth successful season, and it never gets old.  The sight of the first owlet peeking out is always a cause of great excitement.  I am trying to develop a calendar in order to better predict events in their lives.  I have a series of photos if anyone is interested, to which I can supply the link.
 
by the way, both adults are red phase.
 
sue hamilton, calvert county