A small percentage of bluebird eggs are white. Some of the "white" eggs have a pink tinge.
Norma Guidetti indicated that when she saw these eggs in the box, she didn't even think they were bluebird eggs. This is the female's fourth attempt to nest in this box. The other three clutches were also pinkish. Predators got previous eggs (no more than 2 were found before they disappeared. The nestbox is mounted on a pole which is greased. Possible predators might be snakes or large birds, as the nest was not disturbed.)
Norma said she has been bluebirding for 18 years, but this is the first time she's seen pinkish colored eggs.
I have seen Tree Swallow eggs that were distinctly pink (see photo.) White bluebird eggs sometimes have a pinkish caste, but these are REALLY pink! Ann Wick has also see entire clutches of pink bluebird eggs on occasion. Leah of Florida also took a great photo of a clutch of pink eggs (see photo.) Pink eggs would be expected to look the same inside as blue or white eggs. (And no, pink eggs don't hatch into girl bluebirds.)
I asked bluebird expert Keith Kridler why some eggs might be pink. He said "I am just guessing that these egg shells would be thinner than normal if she were able to measure one of the shells. I am guessing that part of the pink tinge to these is actually coming from light going through the thin shell and then the light is bouncing back off the egg yolk giving them this glow. Again I am just guessing but the female just could not pull enough calcium from her diet and body to form thicker more solid colored eggs." It would be interesting to see if there were any change if her diet was supplemented with calcium (either by dusting mealworms or adding calcium sources to suet.)
Steve from Merced, CA noted that Red-shafted Flickers lay pink eggs that look transparent. After a week of being incubated they turn a pale whitish color, losing most or all of the pinkish color, and they no longer look transparent. IF the egg shells are thin and the pink is coming from the light being reflected from inside the eggs, then as the chicks develop they should lose the pink tinge.
Norma provided an update on 7/24/09. All of the eggs hatched. She noted that "During the last week, the eggs were not as pink as when first laid but definitely still had a pinkish hue."
You cannot begin to preserve any species of animal unless you preserve the habitat in which it dwells. Disturb or destroy that habitat and you will exterminate the species as surely as if you had shot it. So conservation means that you have to preserve forest and grassland, river and lake, even the sea itself. This is vital not only for the preservation of animal life generally, but for the future existence of man himself—a point that seems to escape many people.
-Gerald Durrell, The Nature Conservancy
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