Wren in Doubt

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Fairy wrens teach secret passwords to their unborn chicks

Diane Colombelli-Negrel kept 15 nests under constant audio surveillance, and discovered that fairy-wrens call to their unhatched chicks, using a two-second trill with 19 separate elements to it. They call once every four minutes while sitting on their eggs, starting on the 9th day of incubation and carrying on for a week until the eggs hatch.