9 January 2013 Last updated at 07:58

'Monster' bird reveals dark side

Shoebill chick is filmed attacking its younger sibling

Aggressive bullying between bizarre-looking shoebill chicks has been filmed for the first time.

The encounter was captured at Bangweulu wetlands near Kasanka, in northern Zambia, Africa.

Wildlife filmmakers were surprised to witness an older chick attacking its younger sibling while their mother was foraging away from the nest.

The birds are rare subjects for study because their swamp breeding grounds are very difficult to access.

The BBC/Discovery team's aim was to shed light on the species by documenting intimate behaviour of shoebill parents and young at the nest.

Siblicide, the phenomenon of offspring killing their siblings, is common among many larger birds.

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"This behaviour had previously been recorded in shoebills (Balaeniceps rex) but we hadn't planned on seeing it," explained director Alex Lanchester, who describes the shoebill as "prehistoric-looking".

The film, which is at times disturbing, provides intimate footage taken using three mini-cameras fitted to the nest.

The shoebill chicks were approximately three weeks old at the time of filming, with one chick a few days older than the other.

The elder chick can be seen viciously attacking its younger sibling while their parents are absent. It gouges the younger chick with its beak, wounding it and removing clumps of feathers.

The younger chick is also rejected by its parents in favour of its aggressor.

Mr Lanchester describes the scene as "very hard to watch... Especially watching the smaller chick trying to fend for itself, for example trying to shade under the grass and going to get water itself".

The shoebill chick was undeterred by the cameras surrounding its nest

Eventually the younger chick succumbed to its circumstances. "It took about five days for the smaller chick to die," Mr Lanchester told BBC Nature.

"I think it was probably from exhaustion, hunger and thirst rather than a physical injury by the bigger chick."

Survival tactics

The shoebill is an unusual-looking bird that grows up to 1.5m tall with a wingspan over 2m. Its habitat is restricted to Zambia, Sudan, eastern Zaire, Rwanda, Uganda and western Tanzania.

Research suggest the reason for behaviours such as siblicide and offspring rejection is likely to be energy efficiency.

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"It must make sense from a survival point of view, as this huge bird needs to be fully grown within a few months, and the adults probably would not manage to supply enough food for more than one," says Frank Willems, a local ornithologist and ecologist who assisted the filming team.

The shoebill female always lays two eggs but only one ever survives.

Mr Willems commented: "It seems the second egg is just a back-up in case something is wrong with the first one."

"Normally the first to hatch is the one to survive, unless health or growth issues make the second become stronger."

The world population of shoebills is estimated to be between 3,300 and 5,300 according to 2012 statistics from conservation partnership Birdlife International.

Because they live in vast, inaccessible wetlands, there is little knowledge about exact numbers.

Shoebills are only able to rear one chick each year

"The fact that only one chick can fledge per year indicates how sensitive the species is," commented Mr Willems.

"The low reproduction is compensated by very high survival of the adults. A few people removing chicks or shooting adults will make all the difference."

The shoebill is listed as "Vulnerable" on the International Union for Conservation of Nature's global list of threatened plants and animals.

Factors currently threatening the shoebill's future include destruction and quality reduction of its flooded marsh habitat, illegal capture for trade, as well as disturbance or destruction of nests and young.

The footage can be seen on the BBC One/Discovery Africa series at 2100 GMT on Wednesday 9 January.

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