Mangabeys turned up in the eagle nests "more often than chance would predict," according to lead study author McGraw.
"It appears that the [African crowned] eagle specifically targets these large, relatively rare monkeys," he added.
(Related news: "New Monkey Species Discovered in East Africa" [May 2005].)
The new study found that most of the monkeys were dismembered before being taken to the nest.
This, Schultz says, explains how an eagle is able to deal with prey more than twice the bird's body weight.
The behavior also offers an alternate theory for the cause of death of an early human child whose remains were discovered in a cave at Taung, South Africa, in 1924.
The latest research suggests that prehistoric raptors would have been quite capable of successfully attacking a young Australopithecus africanus. The Taung cave specimen weighed around 26 pounds (12 kiolgrams) at death.
"When the Taung baby was discovered, there were several people who proposed that an eagle had perhaps killed it," Schultz said.
"One of the big criticisms of that was the Taung baby would have been way too heavy to be picked up by an eagle. But that's totally misunderstanding the behavior of these eagles."
African crowned eagles have been known to occasionally attack or eat human children, Schultz says.
"There's one report from South Africa of a small child's skull being found in a nest," she added.
What's more, the Taung skull showed puncture marks around its eye sockets, or orbits, that are characteristic of eagle attacks, Schultz says.
"We collected quite a few [monkey] skulls with the same patterns of damage on the back of the eye orbits," she added. "There's one particular skull with identical damage to the Taung baby."
Lee Berger is a human evolution expert at the University of the Witwatersrand in Johannesburg, South Africa, who was not involved in the study. He supports the idea that the Taung child was preyed on by an eagle.
At a conference in Johannesburg last January to mark 80 years of debate over the Taung find, Berger revealed that he had reexamined the skull after hearing of the new Côte d'Ivoire research.
"I almost dropped down when I looked into the eyes of the skull and I saw the marks," he recalled. "I couldn't believe my eyes, as thousands of scientistsincluding myselfhad overlooked this critical damage."
The study authors believe that the Taung child was attacked by a raptor that was about the same size as an African crowned eagle. "There were definitely large, modern-looking eagles around at that time," the University of Liverpool's Schultz said.
Eagles, along with other primate predators, might therefore have played an important role in how early humans evolved, the study team says (human evolution interactive map).
The birds of prey may have influenced an evolutionary move toward group living and bigger body size, for example.
"The larger the group you're in, the more protection you have against predators and the more chance you have of detecting them or fighting them off," Schultz said.
"The other thing you'd probably expect to see is an increase in body size," she added. "A way to reduce your risk is to be bigger, and so harder to catch."
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