All three species of bluebirds – eastern, mountain and western – lay blue eggs. The blue eggs may have white streaks that resemble scratches, which may stem from urine or fecal stains, or when the female turns the eggs.
Eastern bluebirds lay eggs that are powder blue with no dark spots. The eggs have a smooth surface with a subelliptical shape. The mountain bluebird lays eggs that are bluish-white or pale blue, and the eggs are glossy and unmarked. The western bluebird also lays eggs that are light blue or bluish-white. The cell walls along the female's oviduct add coloring to the eggs, but this does not occur with white eggs. White eggs may also have a pink or blue tinge. A small percentage of bluebirds lay white eggs.