Cape gannets (Morus capensis) have a wingpsan of up to 1.8m when fully grown and can live for up to 25 years.
The species breeds in just six places, of which one is Malgas island in South Africa.
Due to people overfishing sardine and anchovies off the coast of Southern Africa, the population of gannets has dwindled.
A change in food supplies is having another deadly impact, however.
Great white pelicans, which can have a 3m wingspan, are starving too, and their hunger is driving them to eat their smaller gannet relatives.
Around 700 pairs of great white pelican nest on the nearby island of Dassen.
Once the pelicans cooperated to hunt freshwater fish, but they soon learnt to eat chicken offal thrown out as waste by a nearby farm. As a result, their numbers increased significantly.
However, that food source has since been stopped, and the pelicans have turned to eating gannets instead.
Each day, hoards of the pelicans fly across to Malgas and wander through the gannet colony.
Safe for now
The pelicans target chicks up to 2kg in weight, picking up any that will fit inside their massive bills and aren't defended by parents.
Because of the fish shortage, often both gannet parents leave their chicks to forage at sea, leaving their offspring particularly vulnerable.
"This unusual behaviour shows how adaptable and opportunistic pelicans need to be," says Patrick Morris, a producer of the Life series who oversaw the filming.
BBC cameramen Justin Maguire filmed the brazen bird behaviour at ground level, while Simon Werry took the aerial shots.
The predatory actions of the pelicans were first revealed by Marta de Ponte Machado, a doctoral student with the Percy FitzPatrick Institute of African Ornithology at the University of Cape Town, South Africa.
She has spent many years studying these birds and helped the BBC camera crew with its filming.
As well as plundering gannet chicks, the great white pelicans have developed a taste for live chicks on their own nesting island, Dassen, feeding on colonial breeders such as Cape cormorants, kelp gulls, swift terns and even African penguins.
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