Douglas Bernard Kirby, of Aptos, had climbed to an elevation of about 16,500 feet on the 19,300-foot Cotopaxi volcano when he did not feel well, decided to turn back and stopped with a climbing guide on an outcropping to drink some water, his brother Robion Kirby said.
"The guide said that after having a drink, he said, 'Isn't life great?' and he slumped back and died immediately," said Kirby, a professor of mathematics at the University of California at Berkeley.
When Douglas Kirby's American friend and fellow climber reached him, "he said Doug still had a smile on his face," his brother said.
Although an autopsy was not performed, the coroner in Ecuador said that Douglas might have suffered a heart attack or stroke, Robion Kirby said.
Douglas Kirby was a senior researcher at ETR Associates in Scotts Valley. He was an avid climber and had recently scaled Mt. McKinley in Alaska, the tallest peak in the U.S., and Mt. Kilimanjaro in Tanzania, Africa, Kirby said.
He had started climbing Cotopaxi with his friend and their guides late the evening of Dec. 21, and the guide had called at 2:28 a.m. on Dec. 22 with the news of his death, Kirby said.
"There has been a large outpouring of messages from people in his profession and from neighbors," Kirby said.
After obtaining a doctorate in sociology from UCLA, Douglas Kirby did research on the Russian military, then obtained a grant to study sexual education and later did extensive research into teen sexual behavior, teen pregnancy and AIDS, his brother said.
He made about eight trips over an eight-year span to Uganda and elsewhere in Africa to study the prevention of the spread of AIDS through condom use and circumcision, which at times brought controversy, Kirby said.
A memorial is planned for Jan. 5 at a church in Aptos, Kirby said.