Can Bluebird Eggs be White?



One of those things that we seem to know for certain is that the sky, bluebird and robin eggs are always blue. BUT at least in the case of bluebird eggs this is not always so. 
I have 25 nest boxes set up for bluebirds and tree swallows and I check these periodically to see how nesting is proceeding. In the previous ten years my bluebird nests have always had blue eggs yet today a new nest I checked had four beautiful white eggs (see photo). Now normally when I see white eggs in a box I assume these would be tree swallows except that the nests are built differently (tree swallows have feathers in them) plus I saw a female bluebird exit the box before I checked it. So I went to the web to get more information and I found that 4-5 % of bluebirds nests may have white eggs: 


In an evolutionary sense, birds that lay eggs in cavities as bluebirds do, would not seem to have any reason to have colored or speckled/camouflaged eggs. So blue eggs are a bit of an anomaly and hard to explain except that they just seem to be perfectly appropriate for a bird that has such amazing blue feathers. Since bluebirds are in the thrush family with the robin (which nests in the open in bushes and trees), it is interesting that various members of this family also have blue eggs so this could be a family trait unrelated to specific nest characteristics. 

Bill Dunson