Starting in September, Southwest Airlines will only allow dogs and cats aboard its planes as emotional-support animals. As for service animals (specially trained to help disabled people), the list will be expanded to include miniature horses.
American Airlines, JetBlue, Delta, and United have each recently adopted similarly stringent standards, with anyone hoping to bring a service or support animal on a plane required to have a note from a licensed medical professional. As CNN notes, "fliers have become increasingly bold in bringing animals on planes," with recent accounts of peacocks, turkeys, snakes, and spiders being brought aboard in the name of service and support.