Bluebird and Small Cavity Nester Conservation
Sialis - Bluebirds and other small cavity nesters



Weird Eggs

Dwarf and Double Bluebird eggs. Photo by L Packer.
Photo by Laura Packer, used with permission

In October, Dorothy Reeves in Erath County, TX discovered two unusual eggs in one nestbox while cleaning. (The egg at the top left is a normal bluebird egg, added for comparative purposes.) Obviously neither hatched. The long egg probably has a double yolk. The small egg was probably laid either right before or after the double-yolker, and probably lacks a yolk. Neither egg was cracked open, so you can't be sure. Keith Kridler of the TX Bluebird Society had never heard of anyone finding both a dwarf and double-yolked egg in the same nestbox. See more weird egg photos and descriptions.

  • Dwarf egg: often lack a yolk, in which case they would not hatch. They may be more spherical than a normal egg, and have a thick, rough shell.
  • "Runt" egg: Noticeably smaller than the smallest extreme expected by normal variation within a clutch. May be different in shape (e.g., more narrow.) A common egg abnormality in domestic fowl, perhaps more common with young birds, not necessarily the first or last egg, may be due to a temporary disturbance in the reproductive system. (Mulvihill)
  • Double-yolked: happens when two yolks are released at the same time, or when one yolk is lost in the body cavity for a day and is picked up by the funnel when the next day's yolk is released. Heredity may be a factor, or it may occur more in young hens just starting to lay.
  • Yolkless: formed around a bit of tissue sloughed off the ovary or oviduct. The tissue stimulates the secreting glands of the oviduct and the yolkless egg results.

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    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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