Wiktionary
chicken tractor
n. A movable enclosure in which chickens can scratch the ground for food.
Wikipedia
Chicken tractor
A chicken tractor (sometimes called an ark) is a movable chicken coop lacking a floor. Chicken tractors may also house other kinds of poultry. Most chicken tractors are a lightly built A-frame which one person can drag about the yard. It may have wheels on one or both ends to make this easier.