Parents need to synchronize the care for their offspring. This leads to extreme and unexpected diversity in how parents attend their nest in shorebirds, finds an international team led by Max Planck researchers. Some pairs switched duties 20 times a day, while in others one parent sat on the nest for up to 50 hours. The key factor underlying this variation is risk of predation, not risk of starvation. Surprisingly, the rhythm of nest attendance often did not follow the 24-h day.