Cameraman swooped by 9kg bird with 13cm claws in quest for footage of world's most powerful eagle in Venezuelan rainforest

As the first people attempting to fit a camera in the nest of the world's most powerful eagle, the BBC filmmakers knew they were likely to be attacked. But nothing could have prepared cameraman James Aldred for the defensive swoop by a 9kg female harpy eagle that left him nearly unconscious, ripped through his neck protection and knocked out his helmet's communication equipment.

The incident, which Aldred survived, was just one particularly dramatic moment in a year of unique footage of the rarely-seen eagle, which eat monkeys and can grow talons up to 13cm long. Shot in the remote Orinoco rainforest in Venezuela, the team filmed a pair of the elusive birds of prey and their chick as it grew into a juvenile.

The eagle's canopy-dwelling habits make it hard to find - the Planet Earth team gave up on it. Once wide-ranging across South America, the bird is now limited to a few strongholds including Venezuela, where the nest was at the fringe of logging operations.

Fergus Beeley, eagle expert and the documentary's producer, said: "I'm amazed by the harpy eagle. These are incredibly intelligent creatures. To kill monkeys, they have to be as intelligent as them, to outwit and ambush them. And it's indisputably the world's most powerful eagle. It has wrists and feet as big as mine."

The harpy, he said, was even stronger than other powerful eagles such as the crowned eagle of Africa and the Phillipines eagle. As well as taking small prey such as sloths and other birds, the species is known to kill red howler monkeys and even the young of the small brocket deer.

Beeley's documentary-makers had to wear protective clothing including helmets, stab-proof kevlar vests and elbow and wrist guards, while working at platforms 40-50m high in a humidity that left them "permanently sweating".

As well as the defensive attack on Aldred, the female harpy eagle hit one man in the kidneys and tore another's leather thigh protection. "Most birds of prey are frightened of people, but this one is not," said Beeley, whose team eventually fitted a nest-cam.

The comings and goings of the harpy eagles have also been recorded in a scientific paper that is currently being reviewed. The documentary, The Monkey-Eating Eagle of the Orinoco' , airs this Thursday at 8pm on BBC Two.