Hornbills will Babysit (IMAGE) Washington University in St. Louis Caption Cooperative breeding is common among hornbills, such as the southern ground hornbill shown here. Studies of this family of birds, which live in Old World tropical regions, suggest that the evolution of this behavior was favored by stable climates. Credit Peter Massas Usage Restrictions Please credit. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.