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The only parrot once common in the US may have gone extinct more recently than thought. According to an analysis of records, the western subspecies of the Carolina parakeet may have clung on until the 1940s, three decades later than previous estimates.

This bright green bird with a red and yellow head was once found in much of the US, with its range stretching from the east coast to Nebraska in the Midwest, and as far south as Florida. 鈥淭he stacks of grain put up in the field are resorted to by flocks of these birds, which frequently cover them so entirely, that they present to the eye the same effect as if a brilliantly coloured carpet had been thrown over them,鈥� .

But Audubon also noted that its numbers were declining rapidly. The species (Conuropsis carolinensis) went , and the last captive bird died in 1918.

Kevin Burgio at the University of Connecticut has been analysing records of Carolina parakeets to try to work out what happened. In 2017, he showed that , and that the ranges of the two subspecies barely overlapped.

Now he has fed his data into a model used to estimate extinction dates. For the western subspecies, the most likely date is 1913, similar to other estimates. But the eastern subspecies, which was mainly found in Florida, clung on until around 1944, the model suggests.

The study may reveal when the parakeets went extinct, but it does not reveal why, says Paul Reillo of the Rare Species Conservatory Foundation. 鈥淭he parakeets鈥� extinctions are a fascinating mystery,鈥� he says.

There鈥檚 no doubt many were killed for food, for fun or to stop them eating crops, but some biologists think habitat destruction or a disease dealt the final blow. Another idea is that honeybees 鈥� an introduced alien in North America 鈥� took over the hollows in trees in which the parakeets used to nest.

The only other parrot once found in the US is the thick-billed parrot (Rhynchopsitta pachyrhyncha). About 1700 survive in Mexico.

Nearly half of all parrot species are now threatened or endangered. Many are likely to join the Carolina parakeet鈥檚 company without swift action, says Reillo.