In order to place an emphasis on how well hens perform in a group, the authors initiated a program of selecting groups of hens that performed well rather than individuals from groups. By selecting groups of birds the authors previously reported a reduction in cannibalism and flightiness that accompanied the improved productivity. In this study they examined various physiological measures to determine if there was an associated physiological change in the birds. They compared lines that had been selected for high and low productivity in groups. The low productivity line (also higher cannibalism and flightiness) had higher blood levels of dopamine and epinephrine and serotonin, and a higher epinephrine/norepinephrine ratio. The birds from the high production line tended to have higher cortisol levels. The differences suggest that the low productivity line were more likely to show the flight or fright reaction to stress (epinephrine etc) indicative of active copers, while the high production line appeared to be more passive. Group selection, which emphasizes the ability to get along in a group, affects various physiological measures in the birds.