杏吧原创

THE speckles on birds鈥� eggshells not only make good camouflage, they could also stop them breaking under their mothers鈥� weight.

A study of eggs laid by great tits (Parus major) has concluded that the spots and speckles have a mechanical role, strengthening the eggshell at its weakest points and so compensating for a shortage of calcium in the mother鈥檚 diet. 鈥淔or a hundred years, people assumed speckling was for camouflage,鈥� says Andrew Gosler of the University of Oxford, whose team analysed patterning and composition of around 90 eggshells. They found that the spottiest eggs came from areas where soils were most deficient in calcium, such as clays. The intensity of pigmentation was highest in the thinnest regions of shell, suggesting it was compensating for lack of calcium.

Gosler doesn鈥檛 deny that some birds have clearly evolved eggshell patterns to provide camouflage, especially shorebirds that lay their eggs directly on exposed beaches. But he argues that his team鈥檚 study, published in Ecology Letters (DOI: 10.1111/j.1461-0248.2005.00816x), applies to smaller songbirds and other species whose eggs don鈥檛 need to be camouflaged because they are hidden from sight. He hopes to test his theory directly by feeding birds set amounts of calcium and counting egg spots.