chicken tractor
n.— «A chicken tractor is basically a bottomless cage or pen of some kind. This is so the chickens can scratch (a chicken’s raison de etre) and eat off of the ground such things as grass, weeds, bugs, etc. In the U.K., chicken tractors are called chicken arks. You can drag your chicken tractor around the yard if you want. They often feature wheels. Without a cage bottom, the chicken manure goes directly onto the ground and becomes fertilizer.» —“Chicken Tractor Gallery” by Katy Skinner The City Chicken (Yacolt, Washington) May 22, 2007. (source: Double-Tongued Dictionary)