Hole-y Eggs

The hard shell of an egg may seem like a thin yet impenetrable fortress. At the microscopic level, though, it’s more like a colander. Thousands of pores allow oxygen into the egg (and carbon dioxide out) so the developing embryo won’t suffocate.

Those pores could potentially allow bacteria into the egg. In most birds, though, a thin layer of protein called the cuticle (or bloom) is added to the outside of the shell just before it’s laid. That layer blocks bacteria from moving inside the egg. Considering that eggs and waste products all pass through the same opening in birds, that cuticle can be extremely valuable. If you’re looking for the cuticle on eggs you bought at the grocery store, you won’t find it. Eggs here in the U.S. are washed before heading to market. The process is surprisingly complex since washing eggs improperly can cause bacteria to enter through those pores. It’s also the reason you’ll find eggs in the refrigerated section. In Europe, the cuticle stays on and eggs are sold at room temperature.

Our understanding of eggshell microstructure impacts Canada Goose populations. The process of “addling” by wildlife management professionals controls the population size of the birds. A thin layer of oil is rubbed on the outside of the eggshell, cutting off the oxygen supply for developing goose. The parents, who see a whole nest full of eggs, stop laying more. But only the un-oiled offspring will survive to hatch. [FYI: it is illegal to do this without a permit – see the Migratory Bird Treaty Act of 1918.]

Dinosaur eggs had pores too, and the structure and placement of those pores tell paleontologists a thing or two about how dinosaurs lived. For instance, some dinosaurs laid eggs in an exposed nest while some buried their eggs. Exposed eggs generally have fewer pores than the buried ones since gas exchange proves more difficult underground. Fewer pores are also found in eggs laid in dry environments to limit water loss. The Museum of Paleontology at Berkley has an excellent site with more information about dinosaur eggs.

Sometimes you DO choose your family (of geese)

What would happen if an adorable 3-day old gosling was placed between two wire enclosures, one containing a sibling, and one containing a same-age gosling from another clutch? Would the baby bird recognize its brother or sister and patter over to its relative?

The answer: yes… at least as often as dentists recommend sugarless gum*. In four out of five trials, the little puffball sidled up to its sibling rather than a stranger’s young’un.

There’s one catch. The youngest goslings (ages 3–9 days) prefer groups. Even if it’s a group of unfamiliar goslings, the little bird almost always waddled over to an unknown group rather than a single relative. By 15 days old though, the youngsters reliably reunite with their kin, no matter how small their family.

p.s. I created this image at an awesome carbon dust workshop, coordinated by GNSI-Carolinas, this weekend. Marlene Hill Donnelly from the Chicago Field Museum was our fearless instructor – she’s wonderful!

*Radesäter, T. 1976. Individual sibling recognition in juvenile Canada geese (Branta canadensis). Canadian Journal of Zoology, 54(7): 1069–1072