Goats, Llamas and Sheep Make Up Landscaping Team at Chicago's O'Hare International Airport

The animals don't charge for work and are happy to do it.

Rather, it's a herd of hooved animals who love green vegetation.

Over 40 grazers, including goats, sheep, llamas, burros and alpacas, graze hilly and rocky areas along creeks part of O'Hare's 8,000-acre property that would be difficult to maintain with traditional landscaping equipment, according to the Chicago Department of Aviation (CDA).

CDA Commisioner Ginger Evans met the herd for the first time on Tuesday, just in time to celebrate the second-year anniversary of O'Hare's Sustainable Vegetation Management Initiative in partnership with Settler's Pond Hooved Animal Shelter and Rescue.

The grazing herd benefits the airport in multiple economic, operational and environmental ways, the CDA says.

In addition to being able to landscape hard-to-reach areas, the animals don't demand pay, for one one thing.

"They don't charge any overtime," Evans told ABC News affiliate WLS. "No, they just nibble away."

The team also happily eats invasive plants that help repel certain problematic wildlife such as birds that could be hazardous to airport operations, according to the CDA.