The Zerbini Family Circus has featured, among other animals, alligators, camels, ponies, and a bison named Tatanka. These animals are intelligent beings who perform not because they choose to, but because they are forced to under the command of human trainers wielding whips and other disciplinary weapons. This circus has been cited year after year by the USDA for failing to provide minimal care for their animals.
Please see recent inspection reports here, including descriptions of camels infested with flies and dangerous enclosures for dogs.
Video of Zerbini Family Circus employee whipping camels: