Wednesday, March 24, 2010

Two Eggs and Counting

Here’s this evening’s shot from the nest box attic cam’. (You can see this morning’s image, too.) As expected, egg no. 2 was laid today.

Gehlbach’s research says an eastern screech owl, Megascops asio, clutch will average 3.75 eggs, if memory serves, so I’m expecting two more eggs, although clutches of up to six eggs are possible.

Note that the eggs are almost spherical, unlike the eggs of (almost?) all other birds. A sphere is a more efficient shape than that of a conventional egg in terms of providing the greatest interior volume for the least surface area. It has been suggested that other birds produce “egg shaped” eggs because, if such eggs start rolling, their shapes will tend to cause them to roll back to their starting-points, all things being equal. Thus in a nest where an egg could do some rolling, the conventional egg shape is the safest. The fact that (most/all?) owl eggs are almost spherical suggests that owls have been cavity nesters longer than any extant bird species, and that evolution has been optimizing the shape of their eggs for efficiency, rather than safety, because rolling out of any proper nest cavity is a non-issue, and therefore there is no survival advantage associated with retaining the conventional “egg shape.”


  1. Anonymous11:20 PM CDT

    Hi Chris,

    I am a brider and owl fan out in Wilco. found your site when I googled "Owl Nest Cams in Austin"

    looks great, hope I get to see your Screech.

    I was looking for local owls for a woman I met on another cam site - wanting to give her tips to find owls/pellets with her kids in Austin. there are on average 17,000 people tuning in to this Barn Owl nest cam. clearly few of them have had observation opportunities - their emotional investment is quite entertaining -

    bon chance with your project - I'll check back. and thank you very much for that global bird cam link - as if I don't spend enough time on line !

    cynthia andrews,

  2. Thanks so much, Chris. I didn't know about the roundness. Thanks, also, for the view. Was confounded about how the heck you saw a thing in there.