How Big Can Eggs Be?

March 06, 2019

MarioFreitas-Jan-29-2019-P1210838b (1)

Photographer: Mario Freitas 
Summary Author: Mario Freitas 

The large ostrich egg in the above picture was bought at a flea market, and the tiny eggshell in foreground fell from a hummingbird’s nest in my garden, last spring. For comparison, I added a midsize chicken’s egg from a corner grocer. The diversity of colors and sizes of avian eggs inspired naturalists and painters like J. J. Audubon (1785-1851), who masterfully depicted birds in their natural habitats.

Measuring the broken shells, we see that the cross-section of this ostrich’s egg is 10 times wider than the hummingbird’s, whereas it’s 20 times thicker. Dependence relation between thickness and size of an eggshell involves properties like porosity, surface area to volume ratio, and mechanical strength. In the picture, a sunlit segment of the broken ostrich’s egg gives evidence to its considerable thickness.

An egg can be exceptionally small, provided that its fragile shell supports the brood bird’s low weight and allows oxygen to diffuse into the egg. But a very big and heavy mother bird would require such a thick eggshell that it couldn't be porous enough for the embryo to breath. For this reason, there's an upper limit for the size of an egg.

Fossil eggs of the extinct Madagascarian elephant bird (Aepyornis) are about twice the width of my ostrich’s egg -- almost at the upper limit for egg size. It should be noted that dinosaur eggs found by paleontologists are never as gigantic as described by most fictional illustrations and adventure books, which are based on the large size  of adult skeletons. Photo taken on January 29, 2019, from Curitiba, Brazil.

Photo Details: Camera: Panasonic DMC-FZ70; Software: ACDSee Pro 6; Exposure Time: 0.0010s (1/1000); Aperture: ƒ/5.4; ISO equivalent: 100; Focal Length (35mm): 166.