At Portland International Airport, a herd of goats lay basking in the sun, taking a nap break from their 24-hour job of chowing down on invasive plants.

Soon afterwards though, the 40 Spanish and Kiko breed goats were back at work, using their nimble lips and sharp back teeth to cut away foliage.

The airport took on the goats to clear a large patch of overgrown land just outside the airfield that is inaccessible to mowers.

The goats, owned by Portland company Goat Power LLC, travel all over Oregon to clear weeds from vineyards, schools and private yards.

"This is our first airport," shepherdess Briana Murphy said. "If they are stuck at home eating hay, "they get really annoyed," she added. "They actually really like working."

The goats were scared of the planes at first, she said, but within days became used to the noise. They will spend three weeks at the airport and clear two hectares of land.

Environmental workers at the airport saw the goats as an opportunity to avoid using harsh chemicals.

"Portland loves its goats. So it wasn't really a tough sell," Port of Portland environmental technician Matt Paroulek said.