BLUE HILL – The smallish black-and-white dog crouches, tense and intent on the group of four sheep at the other end of the ring, waiting for the command.

The crowd in the grandstands at the Blue Hill Fair quiets, and with a word from her handler the dog springs into action.

Guided by a litany of words and whistles, the dog uses instinct and training to herd the sheep through one obstacle after another until they’re shuttled into the final pen.

The crowd shows its appreciation with polite applause and the dog – looking to her handler for the quiet “that’ll do” that tells her work is done – prances happily out of the ring.

People seem to love to watch the dogs work, and the two days of sheepdog trials at the fair have become a popular attraction at Blue Hill, filling the grandstand on Sunday and drawing working dogs and their owners from all over the country.

“It’s exciting. It’s fast-paced,” said Lynn Deschambeault, who runs Merlynn Kennels. Deschambeault showed several dogs at the weekend trials.

The dogs that compete are for the most part border collies, although the trials are open to any working dog. Border collies, however, are among the only dogs that are bred and judged solely for what they do and how they do it, not on how they look, Deschambeault said.

The dogs start their training early, as puppies learning simple obedience, and later, when they’re ready, learning the commands of their trade.

“We start them between 8 months and 1 year, if she’s interested,” Deschambeault said. “We don’t force them to do it; we wait until they show an interest in the sheep.”

The basic commands of “come by” and “away to me” send the dog clockwise and counterclockwise, “lay down” brings the dog up and “walk up” brings it straight ahead. The handler also relies on a small whistle that emits a series of distinctive sounds.

“The whistle tells the dog how far and how quickly you want him to go,” she said. “They can take commands as quickly as you can give them. Sometimes, they can be harder to handle because they’re so quick. They’re gone before you tell them to go.”

The long hours working together form a bond between the dogs and their handlers, one that is evident watching the pairs in and out of the ring.

“A lot of people think its because you’re the one that feeds them, or plays with them,” Deschambeault said. “But it’s the one that works them that they bond with.”

The dogs seem to enjoy the work, and that’s because they’re doing what they’re meant to do, she said.

“They have a tremendous work ethic,” she said. “It’s like nothing else in the world, not even people. On a day like today, you have to be careful with them because they would work until they dropped from the heat.”

As they work the sheep though the different gates, bridges and pens, the dogs earn points for each sheep that goes through an obstacle. The trials are timed, but it’s the points that count. Time only becomes a factor if there’s a tie.

Dogs earn points throughout the season – at venues such as the Blue Hill Fair and, coming up soon, the Fryeburg Fair – as they try to accumulate enough for an invitation to the New England regional meet at the end of the season.

Although the dogs are working dogs, they can make good pets – or, Deschambeault said, they can make terrible pets.

“They’re beautiful. They can learn anything,” she said. “But they do need a job. If they don’t have something to do they can develop bad habits. That might be chasing cars, or herding the neighbors kids on bikes. They love to have a job to do.”