PASSENGERS flying out of San Francisco International Airport recently might have caught a glimpse of something bizarre: goats munching away at overgrown weeds.

Mr Fuzzy, Cookie, Mable, Alice and nearly 400 other goats were chomping on brush as part of the airport's unique - and environmentally friendly - approach to fire prevention.

Airports are mini-cities, often with their own firefighters, baristas, doctors and even priests.

But goat herders? Brush in a remote corner of the airport property needs to be cleared each spring to protect nearby homes from potential fires. But machines or humans can't be used because two endangered species - the San Francisco garter snake and the California red-legged frog - live there.

So for the past five years, the airport has turned to Goats R Us, which charged US$14,900 (S$19,040) for the service this year.

"When passengers take off and fly over the goats, I'm sure that's a thrill," said Ms Terri Oyarzun, who owns and runs the goat-powered brush removal company with her husband Egon and their son Zephyr.

The goats travel 30 miles (50km) each spring from their home in Orinda, California to the airport in a 16-wheel truck that Ms Oyarzun calls her "livestock limo".

With the help of a goat herder and a Border Collie named Toddy Lynn, the goats spend two weeks cutting away a 20-foot (6m) firebreak on the west side of the airport.

When Ms Oyarzun's goats aren't clearing brush at the airport, they are busy doing similar work on the side of California's freeways, at state parks, under long-distance electric lines and anywhere else with overgrown vegetation. The family has about 4,000 total active goats.

Working at an airport does come with its own set of challenges, namely loud, frightening jets constantly taking off.

"There was an adjustment period," Ms Oyarzun said. "But they have a lot of confidence in their herder."

At least one other airport has taken note. Chicago's O'Hare International Airport has requested bids for goats to clear brush in a remote area of the airport's 7,000-acre (2,800-hectare) property and expects a herd to be at the airport sometime this summer.

When goats become too old to work, they are typically sold for meat. But fear not, Mr Fuzzy, Cookie, Mable and Alice won't end up at the slaughterhouse. The Oyarzun family lets its goats peacefully retire at its farm.

At least one part of air travel is still humane.