Variation in Bluebirds Eggs
While monitoring our bluebird nest box we can experience different color and sizes of the eggs. The normal color of the bluebird eggs are rich sky blue, but at time we can find white eggs as well. White eggs are called albanistic eggs. The female will lay either all blue or all white eggs never a mixture. If you do discover one or two different colored eggs in the nest it was cause by egg dumping. Albanistic eggs have been found in all three species of bluebirds nest. The hatching rates between the two show no difference. And there is no connection between white eggs and albinos. About 8% of bluebird’s eggs do no hatch, these eggs are term infertile. This can be caused by several factors, including a defect in the sexual organs of the male or the female, the ingestion of chemicals causing either bird to be sterile or just malnutrition of the female during egg production due to incumbent weather. Also some eggs can be fertile but for some reason stop developing during incubation. Temperature can affect eggs being too cold or over heated. A female bluebird can abandon a clutch after 5 or 6 days of incubation, how she can tell that the eggs will not hatch is not known. She may start building a new nest right over the old eggs, or move to another nest box. Another variation is a very small egg known as a dwarf or runt egg. These eggs are not fully developed inside having no yolk. Another variation is the size of the eggs. Some eggs increase as the egg laying progress continues being that the last egg laid is the largest. With all these variables don’t be too hard on yourself if your bluebirds nesting attempt fails.
