Good friends: Alex’s death was the “worst day” of owner and researcher Pepperberg’s life.David Chandler

"You be good," said Alex last Thursday night. "I love you. See you tomorrow."

But by the next morning Alex, who was 31, was dead of unknown causes. It was "the worst day of my life", says Irene Pepperberg of Brandeis University in Waltham, Massachusetts, the researcher who was Alex's owner and trainer.

Alex was an African grey parrot that Pepperberg bought in a pet store 30 years ago. By the time of his death last Friday, he had a confirmed vocabulary of more than 100 English words that he could apparently understand and use correctly, rather than merely 'parroting' them. Pepperberg has published dozens of scientific papers about Alex's verbal, mathematical and cognitive abilities, and the two have appeared on a wide variety of television programmes and popular press stories. In the process, they have transformed people's understanding of the mental abilities of non-human animals.

A necropsy performed over the weekend found no apparent cause of death. Alex had seemed in fine health the day before, and no problems were found in a checkup less than two weeks earlier.

Bird brain

Besides apparently understanding the meanings of the words he uttered, Alex, whose name was an acronym for Avian Learning EXperiment, could also correctly count up to six (identifying the number of objects on a tray and correctly linking the number he said aloud to the written numeral). He could also identify colours, shapes and materials of various objects. And, occasionally, he could even coin new words to describe an unfamiliar object; he called an apple a "banerry" the first time he was presented with one, perhaps because its outside was the colour of the more familiar cherry, and the inside the colour of banana.

Pepperberg's research remains controversial, with some skeptics maintaining that Alex's apparent mastery of language revealed nothing more than a very sophisticated version of conditioned responses. Pepperberg says that is hard to reconcile with such findings as Alex's 80% accuracy in counting objects. In her peer-reviewed papers, she has said that he seemed to have intelligence comparable to a five-year-old child, but emotional behaviour more like a two-year-old.

For example, when frustrated or annoyed, Alex would sometimes give wrong answers to all of the questions put to him - a result that Pepperberg argued could not be due to chance, but required knowing all the right answers and refusing to give them, as a petulant child might do.

Losing Alex

The research will continue, Pepperberg says, but "losing Alex is a huge issue" that will set back her planned work, including a new grant for research on parrots' perception of optical illusions.

"We do have two more birds," she says, who have been through years of training. But their language abilities lag far behind what Alex displayed. The second-oldest, a 12-year-old parrot named Griffin, has mastered fully only 20 words, and is still working on full comprehension of 12 more. For example, when asked the colour of an object, he will always answer with the name of a colour, but not necessarily the right one, so those words are not yet counted as part of his fully understood vocabulary.

When asked to summarize the impact of her three decades of parrot research, Pepperberg says "people think much more seriously about the intellectual abilities of these feathered creatures." She says her work has influenced other groups who have since investigated the intelligence of other birds, including crows. "I like to think that being called a birdbrain is now a compliment."

Pepperberg says they have not yet settled on any plans for a funeral or other ceremony.

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