The parrot which worked with US scientists for 30 years and helped them conclude the species' intellect can match that of a five-year-old child has died.
Alex the African grey parrot could count to six, identify colours and even express frustration with repetitive scientific trials.
The cause of Alex's death was unknown. The African grey parrot's average life span is 50 years, Brandeis University scientist Irene Pepperberg said.
Alex was discovered dead in his cage on Friday, she said, but she waited to release the news until this week so grieving researchers could get over the shock and talk about it.
"It's devastating to lose an individual you've worked with pretty much every day for 30 years," Pepperberg told The Boston Globe.
"Someone was working with him eight to 12 hours every day of his life."
Alex's advanced language and recognition skills revolutionised the understanding of the avian brain.
After Pepperberg bought Alex from an animal shop in 1973, the parrot learned enough English to identify 50 objects, seven colours and five shapes.
He could count up to six, including zero, was able to express desires, including his frustration with the repetitive research.
He also occasionally instructed two other parrots at the lab to "talk better" if they mumbled, though it wasn't clear whether he was simply mimicking researchers.
Alex hadn't reached his full cognitive potential and was demonstrating the ability to take distinct sounds from words he knew and combine them to form new words, Pepperberg said. Just last month, he pronounced the word "seven" for the first time.
The last time Pepperberg saw Alex was Thursday, she said. They went through their back-and-forth goodnight routine, which always varied slightly and in which she told him it was time to go in the cage.
She recalls the bird said: "You be good. I love you."
She responded, "I love you, too."
The bird said, "You'll be in tomorrow," and she responded, "Yes, I'll be in tomorrow."
I reacon it was from mad parrot disease or bird flue..