When students at Indiana University of Pennsylvania went home for the summer, many of them left something behind: their pets.

Officials at animal shelters in Indiana and several other college towns say they have seen an increase in stray cats and dogs since the school year ended.

"It happens every summer," said Jill Carnahan, of the Indiana County Humane Society. There are about 200 cats and 48 dogs currently at the nonprofit shelter, double the normal number, and many are brought in by students or landlords who find them.

Nancy Peterson, an issues specialist with the Washington-based Humane Society of the United States, said college students' abandoning pets is a perennial problem.

"It's hard for a young college student to think 10, 15, 20 years into the future. But many of our cats and dogs are living that long and where you'll be in that time is so uncertain," Peterson said.

Most colleges don't allow students to have pets in dorm rooms, and many humane societies won't allow students to adopt animals.

"Most colleges don't allow pets because they know the student's life is filled with many distractions and responsibilities that would make it difficult to be a responsible pet owner," Peterson said. "That's during the school year, so what happens when the school year ends?"

At Indiana University of Pennsylvania, a state school, pets are not allowed in residence halls. About 4,000 of the school's 13,500 students live in dorms, though, leaving many more in off-campus housing where the rules on pets vary.

Carnahan said often students can't afford to have their pets spayed or neutered, and the shelter ends up finding hungry or sick animals left behind. Providing medical care for the stray animals at the shelter can be expensive and taxing on the paid and volunteer staff, she said.

Currently, the shelter is offering a "Two Fur One" promotion for anyone who will take two cats or kittens. In many cases, though, the animals will have to be euthanized.