red - brown speckles on bird-eggs can reveal presence of the insecticide ddt in the environment. A study from the Oxford and Cardiff universities on the eggs of raptors -- a group of carnivorous
birds -- has found a link between the speckles, the presence of ddt and calcium deficiency. The insecticide acts as
a calcium blocker in eggshells, giving them a speckled look. Researchers say this could be an inexpensive and safe method for monitoring ddt contamination in the environment. Previous studies have explained the link by studying the calcium transport in eggs of
another group of birds; passerines.
The study has evolutionary significant for raptors, which eat the bones of their prey and are not normally calcium stressed. The researchers say that 'speckling' to strengthen eggshells seems to have been conserved over evolution, suggesting it is an essential character in maintaining the strength of the shell.
Photoporphyrin deposits are signs of lack of calcium as well since more speckles are found on thinner patches of the shells--which lack calcium. Both the calcium and photoporphyrin are carried by the same enzyme from the shell gland and deposited on the shell. If calcium supply is inadequate, the enzyme can carry more photoporphyrin, leading to more speckles.
The eggs studied were found to have ddt levels ranging from 10-30 parts per million. The paper says though this link can't be generalised, this could be a useful indicator of ddt contamination for raptors. The study was published in the online edition of the Journal of Applied Ecology and is slated for publication in 2008.
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