Chicken Rank: Hen social position shifts egg hormones
By Susan Milius
A study of leghorn chickens has linked hormone concentrations in a hen’s eggs to her rank in the pecking order.
The yolks of low-ranking hens’ eggs harboring males have about the same concentrations of testosterone and one of its chemical precursors as do yolks of eggs containing female embryos, says Wendt Müller of the University of Groningen in the Netherlands. The male-to-be eggs of top females, however, have an extra dose of these hormones, Müller and his colleagues report in an upcoming Proceedings of the Royal Society of London B. The researchers speculate that parental investment of extra male hormones may make chicks more robust, competitive, and therefore more likely to reproduce.