Richard Levenson at the University of California, Davis, and his colleagues showed pigeons microscope images of breast tissue. Then they rewarded them when they correctly pecked a coloured button that corresponded to either cancerous or healthy tissue. After 15 daily sessions, each lasting an hour, the pigeons got the right answer 85 per cent of the time.

Pooling responses from a panel of four pigeons, or “flock-sourcing” as the researchers call it, increased accuracy to 99 per cent. The pigeons were just as good at spotting small calcium deposits associated with cancer, which appear as white specks on mammograms.