It is well known that most birds will lay their eggs with the sunrise, but this is not the case for robins. A robin will lay her egg in the middle of the morning instead. There is a good reason, though. A robin will eat a whole lot of earthworms when it is the season for breeding, and they will hunt for them in the early hours when the worms are mostly available. Only after their worm feast will they lay an egg. After a nice hearty breakfast, laying an egg is easier for the robin, whereas other types of birds seem to need a long, quiet period of time in order to lay.
Robins can only lay one egg a day, and that is hard work! A female bird only has one working ovary. Mammals, on the other hand, have two. The ovaries are part of the reproductive organs where the eggs are created. When looking at a bird’s ovary, it looks like a bunch of grapes that are different sizes. The “grapes” are the bird’s ova, or the yolks. The egg that is next in line to be laid is the largest. The others are smaller, based on when they will be laid. Once a day, the one that is the largest is ovulated. That means that it will pop off of the ovary and begin going down a tube, called the oviduct, that goes throughout the robin’s body.
The egg will be fertile if the robin has mated. If not, it will still go down the oviduct and be laid like any other egg, but it will not become a baby bird. As the egg makes its way through the oviduct, the surfaces of the wall produce albumen to surround the yolk. Albumen is a healthy protein that is watery. As the yolk nears the end over the oviduct, it is surrounded by calcium compounds, thus creating the shell of the egg. This entire process is very draining on the body of the robin!
Below is a video of hatching robin eggs. Such a beautiful display of nature at its finest!