80 chickens (40 males and 40 females) of an F7 intercross between red jungle fowl and White Leghorn layers were used in the study. 

The red jungle fowl are the ancestor of all domesticated chickens, whereas the White Leghorn layers are one of the breeds commonly used in egg production. 

The birds were kept in adjacent pens, separeted by gender, about 40 birds/pen, at the chicken facility Wood-Gush at Vreta Agricultural School outside Linköping. The birds had full visual and auditory contact with each other and all followed the same standard routines.

The birds that took part in the study were randomly chosen at the beginning of the first test, likewise was the the order for the 80 birds randomized for each of the tests.