As wild animal lovers are not content with watching tigers and gorillas  during the day, a growing number of zoos in the US are offering a more thrilling after-dark experience -- overnight stays. The Philadelphia Zoo is America's first zoo and home to more than 1,300 animals. It has been running its Roars and Snores Overnight Programs for about 20 years. The most popular theme program is the Night Flight Overnight Program where children aged 5 to 12 sleep in the zoo's tree house. The overnight stays are not only popular with young children. Most overnight stays include a night tour during which youngsters experience the mysterious sights and unusual sounds of the zoo. A midnight snack and breakfast are also served. "It is a unique experience to be at the zoo without the crowds and additional noise," explained Patterson, of the Denver Zoo, which has been running its Bunk with the Beasts program since 1998. With nearly 4,000 animals and 700 species the zoo attracts more than 1.8 million visitors a year. "The things you hear and see in the zoo are completely different," said Patterson. On Denver's two-hour tours, night vision scopes are provided so guests can see nocturnal   animals such as owls, and indoor educational games increase the learning experience. Patterson said parents tend to be more worried about leaving their children than the children themselves. They have rarely had to call up a parent in the middle of the night. "They love it," Patterson said about the children. "For many, it's their first overnight stay away from home. They are so excited that by the end of the day they are so tired that they have no opportunity to worry." "Guests at the new overnight program at the Queens Zoo make breakfast treats for animals, and watch the keepers feed them to the animals," said Education Curator Tome Hurtubise. The growing popularity of overnight programs has caused zoos that only serve day-time visitors to think again. The Queens Zoo, which started their program this year, is so pleased with its success that they want to continue it next year. What can we conclude from the passage?
The Philadelphia Zoo is America's biggest zoo. It is becoming so popular that American zoos are open to visitors at night. Roars and Snores Overnight Programs are most popular. The overnight stay program is only for children.