Chicken Rank: Hen social position shifts egg hormones

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.