Birds nest in trees, on the ground, on water, among cliffs, and in caves. They build their nurseries from plant materials, mud, dung, saliva, spider silk, pebbles, and animal hair. Some nests have roofs or multiple rooms. Some are simple scraped depressions in the earth or natural cavities in trees.
Most songbirds construct cup-shaped nests which require about 1000 trips to bring in building materials (1). The birds use their feet to scrape, chests to push, and beaks to manipulate twigs and grasses as they rotate. Exhausting! Why go to such an extreme effort? Predators. Birds living on predator-free islands nest on the ground.
Some ground-nesting birds have other ways of avoiding predators… like teaming up with defenders. The red-breasted goose of Siberia nests next to peregrine falcons. The geese act as look-outs for foxes; the falcons attack. Some birds build their nests in ant or termite colonies to protect the eggs.
These sleeping bird babies, pictured, are cardinals. Their parents built this camouflaged nest in the crook of a pear tree. If dad hadn’t stopped by with some breakfast, I would have never realized they were there.
- Collias, N.E. 1964. The Evolution of Nests and Nest Building in Birds. American Zoologist. 4: 175-190.
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.