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.”