Spring is Time for Eggs

-by Wildlife Educator, Ben Betterly

So what did come first, the chicken or the egg? This age-old causality dilemma has perplexed humans since the dawn of civilization. To ancient philosophers, the question about the first chicken or egg evoked the questions of how life, and the universe in general, began.  Charles Darwin’s theory of biological evolution via natural selection set the story straight, or at least changed the question. We now know that the egg predated the chicken, as chickens (and all other birds) share a common ancestor with reptiles, which also lay eggs.

Spring is the time that egg-layers lay their eggs; and different species have different strategies.  Many birds, of course, build nests in which to lay their eggs. Other animals build nests too, but birds do so in an extraordinary variety of forms, materials, and sites.  In the Northwoods, the Bald Eagle takes the prize for the largest nest, which can measure up to 6 ft. in diameter and weigh upwards of 2 tons (4000 lbs)!  The smallest nest (and eggs) goes to the Ruby-Throated Hummingbird, which produce structures merely 2 in. in diameter.

Song Sparrow Nest and Egg
(C) Ben Betterly

Many birds build nests in the branches of trees, but not all do. Song Sparrows will often build their nests directly on the ground.  Natural selection has provided their eggs with camouflage (light brown, with a spackling of dark brown) to avoid being seen and eaten by potential predators.  Only birds lay eggs with pigmented colored shells; and some birds such as American Robin (and others in the Thrush family) lay bright blue eggs! Scientists are still not sure of the function of the blue coloration, and it’s hard to imagine how natural selection would allow such a brightly colored egg to persist. For one thing, Robins make their nests high among tree branches where their eggs will be kept relatively safe from hungry predators.

Most birds put a great amount of effort in brooding their hatch. They must first select a proper site, build a nest, lay their eggs, incubate, and once hatched, take vigorous care of their chicks.  Few reptiles can compare to the parenting determination of birds (although evidence suggests that some Dinosaurs had highly developed parenting behaviors).  Most Reptiles such as many turtles, simply find a suitable a spot to drop off their eggs, and hope for the best. 

A snapping turtle lays her eggs right
in the Center's parking lot!
(c)Licia Johnson

Snapping turtles will often travel extensively overland, away from their aquatic habitat to lay their eggs in sandy soil.  After digging a hole, the female deposits her eggs and covers them with sand for incubation and protection.  Unfortunately, snappers often choose to lay their eggs on the shoulder of busy highways. While this might make a good substrate for incubation, it can be dangerous for both the mother and her offspring.  Too often, turtles are hit and killed by drivers; and while natural selection has provided them with a hard protective shell, they’re no match for a car.   If you see a turtle laying its eggs on the side of the road, please make sure to give it some room; and if you happen to come across a turtle in the middle of the road, you can gently encourage it to keep moving on with its journey. 

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If you want to read a bit more on the subject of eggs - here's a cool article on science daily news about the intensity of color in robins eggs correlating to the degree of parental care.