There was a link to this posted in a previous thread:
Chickens usually prefer to do this together and with the same rhythm. The eye of a wild living chicken is focused for a view of five meters to see grains and other small things and for a view of 50 meters to see larger things. That's why chickens do not like to go away from their hen house farther than 50 meters.
http://www.chicken-yard.net/general/behavior.html
http://www.chicken-yard.net/general/behavior.html