When the weather was hot, the birds produced a fast, high-pitched call around their eggs. ‘To find out whether there was any effect on the embryo, we did an incubator experiment,’ she says. They found that unborn chicks sung to in this way were smaller and lighter when they hatched, which helped them cope better with the heat.
‘It’s exciting,’ says Mariette. ‘It has implications for the stage at which birds start learning sounds.’ Her team is now looking at how this remarkable heat song works.