A 35-large team of sheep, goats, and a donkey named Jackson is working to maintain the vegetation near an airfield at O’Hare International Airport, eating through steep areas difficult for lawnmowers to maneuver.

The program, now in its fifth year, is getting its animals this season for the first time from contractor Carpathia and will cost the Chicago Department of Aviation $11.50 per animal per day. The four-legged crew began grazing a week and a half ago and will work through mid-November, but two days ago moved to a new area, where it has already reduced vegetation significantly.

“Because this is an environmentally friendly alternative and one that we believe is cost-effective, we’re very happy to support it,” says Aaron Frame, deputy commissioner of environment for the aviation department. The natural method frees up department staff to maintain and mow other areas, and Frame says it also helps the department reduce air pollution and herbicide emissions.

The animals have 35 acres of vegetation to eat this fall, but Frame says the Department of Aviation has identified 100 acres total for the program. Situated outside the airfield security fence, the area is nothing more than a buffer zone for aircraft. Still, vegetation that grows too tall becomes a habitat for birds that pose a risk for aircraft. To mitigate, shepherd Andrew Tokarz moves his herd around the 35 acres and adjusts the number of animals depending on area needs.

Loud conditions at O’Hare haven’t affected the animals through five summers, according to Frame. “Surprisingly, the animals adapted very well. They don’t seem to be agitated in the least, and they seem to be performing quite well.”

Rest assured, Jackson and the goats appeared to be in good spirits as they inspected and licked reporters Thursday morning.