58 Birds that are helpless on hatching, such as blue tits, usually grow at an extremely fast rate, fuelled by a constant supply of food from their parents. Many studies of wild birds monitor nests in boxes, such as this brood of blue tits. Photos like these are taken by specially trained scientists who ensure the welfare of the birds. Leg Wing Mouth brightly coloured to attract attention Joined eyelids Feather tract Feather tufts Feather sheaths 1 One day old Twenty-four hours after hatching, blue tit nestlings have no feathers and their eyes are closed. Their parents bring food to the nest every few minutes. Julia Schroeder Researcher Julia Schroeder studies the behaviour of birds across generations on Lundy Island, UK. Every year, she monitors different birds including hundreds of sparrow chicks in nest boxes, and has discovered that noise pollution is harming young sparrows. EYEWITNESS 2 Three days old Small tufts of feathers have appeared and the nestlings are about four times heavier than when they hatched. 3 Five days old Dark grey feather tracts have appeared on the backs and wings. These areas will produce the birds’ feathers. A wren may make 1,000 trips a day to feed its chicks .