House Sparrow (IMAGE) Max-Planck-Gesellschaft Caption Hormones are important signaling molecules. The nestling number of the house sparrow depends on prolactin and corticosterone. Credit istockphoto Usage Restrictions These images may only be used or reproduced for editorial purposes and in connection with scientific articles on our press material, in which case such usage or reproduction is free of charge and requires no permission. Any other use, in particular for commercial purposes, requires prior permission of the author or photographer. Further enquires can be answered in the Press and Public Relations Office - simply write an e-mail to gebhard@gv.mpg.de. 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.