Thursday, January 29, 2009
Birds that know when to hide their beauty
For a great deal of the year the golden plover struts conspicuously among the dune grasses and heathers of its moorland breeding ground. It has striking black and white plumage on the front, and a broken, spangled pattern on a golden-brown back. But when the time comes to incubate its eggs, it cannot afford to draw attention to itself. It is then that the plumage on a female's back shows its value as camouflage.
As the hen crouches low on the nest, her back blends in with the surrounding carpet of windblown, flower-speckled grass. She is practically invisible from above and from the sides. Thus her eggs are able to hatch in safety.
A relative of the golden plover, the eye-catching blacksmith plover of tree-scattered African grassland, is so conspicuous in its black and white feathers that it would be futile for it to attempt to blend with its background. Its nesting technique, though, is of startling originality - it often lays its dark, mottled eggs in a pile of zebra dung, which is probably the last place any hungry predator would think of looking for a meal.
Another relative is the ringed plover - a wader that breeds on rocky coasts. Rejecting formal nest building, it lays its mottled eggs straight onto the shingle, from which they are indistinguishable. The adult is similarly camouflaged, with sandy wings and black and white head. The downy chicks are equally difficult to see against the pebbles and debris of the shore.
It takes a very good disguise to enalbe a bird to sleep safely on the ground by day. The white-throated nightjar hunts moths at night; but at daylight, it selects a spot among the dried vegetation, where it is practically invisible. It is probably more at risk there from being trodden on than from being attacked by a predator.