Powerful synthetic insecticides such as DDT were poisoning food chains, from insects upwards. It would provide an unequivocal identification of the bird killers. For most of 1961, she had locked herself in her cottage in Colesville, Maryland, to complete her book, Silent Spring. Several causes were proposed – poisons, viruses or other disease agents – but no one had a definitive answer or seemed sure of the cause – with one exception: the biologist Rachel Carson. Something was happening to the birds of the western world. Ornithologists also noted eggs were often not being laid while many that were laid did not hatch. For years, reports in the US indicated that numbers of birds, including America's national bird, the bald eagle, were dropping alarmingly.
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