Nothing says spring like seeing a robin poking in the yard, but there's something about finding a nest full of light blue eggs that always brings a smile. The American Robin has been building nests in neighbourhood backyards for centuries, but the mystery of why their eggs are blue continues to confound naturalists.
Robin eggs defined the shade, "robin's egg blue." The hue is now the official Crayola colour #97 and the name "robin egg blue" has been trademarked by Tiffany and Co.
Robin eggs are light blue, slightly turquoise in colour and unmarked. They are about 1.1 to 1.2 inches in length and about 0.8 inches in width.
It is not known why the eggs are blue but evidence suggests that for the same reason birds that nest on or near the ground generally lay brown or grey eggs, the blue tint of eggs in trees might help them be camouflaged by overhanging leaves and shadow.
When trying to identify eggs, one clue is the size of the nest and how it is built. Only the female robin works on the nest, using her bill and feet to add twigs, grasses and feathers and her breast to smooth pads of mud into a solid bowl-shaped nest approximately six inches across with a hollow that will fit a softball. The father spends very little time at the nest or brooding the eggs but will return to assist with feeding and protecting the nestlings.
Robins have become so accustomed to civilisation that they'll often build their nests over back door lamps, on windowsills or on top of electrical boxes.
The first eggs of the season will arrive in clutches of three to five. If a second clutch is laid later in summer, it will usually only have two eggs.
Eggs are usually laid one per day. The mother robin will then sit on the eggs, keeping them warm and turning them often for about 14 days after the last egg is laid.
Other Blue Eggs
Bluebirds also lay blue eggs, but their eggs are smaller than those of the robin--about the size of a dime--and are generally laid in nests that are deeper and more cylindrical.
Robin eggs are favoured by snakes, crows, jays, squirrels and raccoons and it is not uncommon to see the parents dive-bombing predators that come too close to their nest. If you find a nest, it's best to leave it alone--chances are the parents aren't far away.