September 7, 2005
Why Are Birds’ Eggs Speckled?
Birds' eggs are unique in their diverse pigmentation. This diversity is greatest amongst perching birds (order Passeriformes: 60% of all bird species), which include many familiar species including tits and warblers. Despite intense interest, the purpose, in most species, of these patterns was unknown.
Most passerines lay eggs speckled with reddish protoporphyrin spots forming a ring around the egg's blunt end, on an otherwise unpigmented shell. Evidence in a paper by Gosler, Higham & Reynolds soon to appear in Ecology Letters now suggests that rather than giving a visual signal, protoporphyrins strengthen the eggshell by compensating for reduced eggshell-thickness caused by calcium deficiency.
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