These bluebirds are residents here all year. The first was abandoned but we now have eggs and chicks in two nest boxes. After cool weather, it is now warmer and insects have hatched for parent birds to stuff in the wide beaks of demanding youngsters. They often fly to the ground from a perch for a morsel invisible to us. From a distance, the male plumage looks slate-blue but close-up in the sun they are gorgeous blue and rouge. Evidently, the blue color is created by light scattering (like a prism) whereas pigment is responsible for their sky blue eggshells. Why they are blue to match plumage when many other cavity nesters have white eggs with or without speckles is a question I can’t answer. Recent research confirms that birds tend to be more colorful in the tropics, but our bluebirds are among many exceptions to the rule.
By Roger Gosden
A British and American scientist specializing in reproduction & embryology whose career spanned from Cambridge to Cornell's Weill Medical College in NYC. He married Lucinda Veeck, the embryologist for the first successful IVF team in America. They retired to Virginia, where he became a master naturalist and writer affiliated with William & Mary. https://en.wikipedia.org/wiki/Roger_GosdenView all of Roger Gosden's posts.