Thirty or 40 years ago, the summer tourist season for Yellowstone and Grand Teton national parks fit nicely between Memorial Day and Labor Day - perfect for U.S. college students who wanted summer jobs in the parks.

Today, changing demographics have expanded the summer season into the "shoulder" seasons of spring and fall, which doesn't work as well for U.S. college students, or for Xanterra Parks and Resorts, the dominant concessionaire at Yellowstone. The company operates hotels, campgrounds, restaurants and gift shops.

Jim McCaleb, general manager of Xanterra's Yellowstone operations, said he has to hire 3,400 people to fill 2,600 jobs for the expanded summer season. Xanterra still hires U.S. college students, but has found good workers with flexible schedules in the ranks of some 1,000 international college students.

"We have international student workers from just about everywhere," said McCaleb, who first came to Yellowstone in 1985 as a college student from the University of Tennessee. Last year, Xanterra hired summer workers from 40 countries, all 50 states and the District of Columbia.

McCaleb said Xanterra works with international employment agencies and attends job fairs all over the world. Most of the international workers come to the United States on J-1 visas, which cover a wide range of exchange visitor programs sponsored by schools, businesses, and a variety of organizations and institutions. Others come in on H-2B work visas, to take temporary or seasonal non-agricultural jobs.

All of Xanterra's summer hires, domestic or foreign, are extensively interviewed to confirm excellent English skills, well-oriented, are settled in to on-site dorms and are paid the same, McCaleb said. Commuting from gateway communities just isn't a viable option.

"We house and feed them, and work is just a short walk away. Our workers integrate quickly and develop a real love for the park. Many come back for more than one season," he said.

That's certainly true for Rafael Mendez, 22, a mathematics and civil engineering student in Bogota, Colombia. He works as a gardener and in the Xanterra laundry, and on his days off, he teaches Spanish to a family that lives in the park.

"I love the park, and I came back to see my friends," said Mendez, who hosted his family from Colombia on a visit last year.

Colombia has national parks too, but nothing quite like Yellowstone, he said. He convinced a Bogota friend to come work with him at Yellowstone, to be greeted by a spring snowstorm. "She was amazed," he said with a laugh.

Jared Khoo, 24, of Singapore is another Xanterra employee in Yellowstone, staffing the gift shop at the Lake Hotel.

"I thought Yellowstone would be a big safari park, but it is much larger and more dangerous" with wild animals walking about, Khoo said. Still, he has enjoyed hiking in the park and relishes the international flavor of his dorm - fellow students from Colombia, Serbia, Jamaica and South Africa.

Grand Teton National Park faces a similar situation in finding a summer concessionaire work force, only it has numerous concessionaires instead of one big one like Xanterra. According to Grand Teton spokeswoman Jackie Skaggs, the park has 27 concession contracts and 45 commercial use permittees. Grand Teton National Park has an orientation and interpretive training course for all 1,800 concessionaire employees in the park, of which 1,000 work for Grand Teton Lodge Co. and about 200 for Signal Mountain Lodge.

Skaggs said the park doesn't have a tally of international workers, and the Grand Teton Lodge Co. has declined comment on how many of its workers are foreign.

At a tourism conference last year, however, Bob O'Neil of Jackson Lake Lodge said he recruits foreign workers because he can't find enough U.S. workers. He said foreign workers get terrific experience working in the United States, which they take home.