FEDERAL guidelines in America stipulate that airlines must allow passengers with disabilities to bring support animals onto flights. The rules were originally designed with guide dogs for the blind and the like in mind. Yet in recent years the rules have allowed a host of unusual and exotic animals to board planes for their owners’ emotional wellbeing.

Last weekend United Airlines, America’s third-largest carrier, drew the line at a peacock. A woman arrived at Newark International Airport and attempted to board her flight with the large bird, which she claimed was an emotional-support animal. The Jet Set, a travel show, captured images of the bird as it was denied boarding (see picture). The airline told the Washington Post that the peacock “did not meet guidelines for a number of reasons, including its weight and size” and that “we explained this to the customer on three separate occasions before they arrived at the airport.”

Service animals, including emotional-support animals, can generally fly for free. As a result airlines are worrying that people are avoiding paying to transport their pets by claiming they serve a therapeutic role. According to Delta Air Lines, America’s second largest carrier, the number of comfort and service animals on its planes has increased by 150% since 2015 (albeit from a low base). The animals do not always behave. Delta reports an 84% increase since 2016 in incidents involving poorly-trained pets that bite passengers or crew members, urinate or defecate on them, or otherwise cause a scene. Delta is now adopting stricter rules for emotional-support animals, requiring a doctor’s note, health and vaccination records, and a signed confirmation that the animal can behave on a flight. The airline will not allow certain kinds of animals, including snakes, goats, reptiles, amphibians, beasts with horns, and anything that emits an odour (except humans).

Some people have argued against these restrictions. There are certainly travellers who benefit from the company of a support animal. But there is no question that airlines’ permissiveness has been abused in some cases, or that innocent passengers sometimes pay a brutal price for the misbehaviour of their furry or feathered neighbours. It is very likely that other airlines in America will follow Delta’s lead in laying out restrictions.

Another solution would be to sell tickets for well-behaved pets to travel in the cabin, meaning that nervous owners would not be separated from their companions when travelling. The Gulf carriers—the arch-rival of the big three in America—have much more flexible policies for some birds. Emirates of Dubai, Etihad of Abu Dhabi and Qatar Airways all allow falcons in the main cabin on at least some of their flights, as falconry is a popular sport among the wealthy in the region. Extending such a policy to other caged birds would not be a feather-brained idea.