I thought I’d answer a question or two I received over the years about bird eggs and “throw in” some more information. Birds, reptiles and a few other animals lay eggs. All birds produce eggs with a thin, hard shell. Turtles, and some snakes, produce eggs with a leathery or more flexible shell. Birds lay their eggs in nests, which vary by species, and so do the eggs vary in size, shape and coloration.

The question I’ve received most often is why do birds only lay one egg a day? A fox, cottontail rabbit, or a mouse give birth to litters of multiple young all at one time. But remember, they are not concerned about weight conservation to allow them to fly. If a female robin developed four or five eggs and carried them inside her until laying all in one day, she wouldn’t be able to get off the ground. She, and bluebirds, grouse, swallows, etc. all lay one egg a day. Many raptors, like eagles, lay an egg every other day. So limiting its body weight is a major factor in the one egg a day process.

How does a developing chick breathe inside a shell? Depending on the size of the egg, the shell can contain 10,000 to 16,000 microscopic pores that allow the exchange of gases. Just before hatching, the young bird develops an egg tooth to help it crack the shell. Once cracked, it eventually can work itself free of the shell. The adult birds will remove the eggshell quickly to help the young and nest remain hidden. This is why you may find a blue robin eggshell 70 or 80 feet from any trees.

I recently wrote a column on the screech owl and I was able to photograph a female screech owl and her eggs. Screech owl eggs are white and more rounded. In fact most cavity nesting birds have white or plain eggs. In a dark cavity, why do they need patterned eggs? However, killdeer, plovers or an American oystercatcher lay their eggs on the ground or sand. A bright blue or all white egg would “stick out like a sore thumb.” Almost all ground nesters have dull colored or patterned eggs.

Another trait of eggs is their shape. The screech owl nest contained nearly round eggs. My assumption, which is still partly correct, is that inside a cavity, they really can’t roll away. In contrast, birds nesting on cliffs or ledges, have eggs which are more asymmetrical (more pointed at one end). If bumped in the nest they are less likely to roll out but roll in a circle.

However, note, I said partly correct. It appears that studies of birds all over the world reveal that the speediest and longest flying birds have the most asymmetric eggs. That shape fits best with their already streamlined bodies. It so happens that those “speedy” birds are often cliff nesters too.

Birds mate prior to egg laying. The egg is fertilized inside the female before the shell is formed. The yolk of an egg provides the necessary food for the developing chick inside it. The chick development begins when incubation (birds warming the eggs) begins. In passerine birds: i.e. robins, bluebirds, incubation begins when the last of the eggs are laid. In raptors, incubation begins when the first egg is laid.

I hope this answers a few egg questions, and even though it wasn’t “egg-citing,” you may have learned a thing or two. Hey, get out there …

Test Your Outdoor Knowledge: True/False A bird’s eggshell is composed of calcium carbonate.

Last Week’s Trivia Answer: The eastern coyote is considerably larger then its western counterpart.

Of special interest, if an early riser, you can soon expect the early morning singing of the male robins, cardinals and titmice to “shut down” in the next week. As breeding season wanes, the males no longer need to sing to “protect” their nesting areas from competitors. The mornings will become eerily quieter ...

Contact Barry Reed at breed71@gmail.com.