This is the heartbreaking moment a mother brown bear leaves her cubs to make their own way in the world.

These extraordinary pictures show how she stands close to her babies, pauses for a last look, and then without a backward glance, swims across the world's fifth longest river, never to see her offspring again.

The images from Russia highlight a coming of age ritual in nature, the final farewell of a mother to her offspring, a sight seldom glimpsed in the outside world.

This is the final moment a female bear says a final goodbye to her two cubs before leaving

The mother abandoned the two cubs, who are old enough to fend for themselves in Siberia

The two cubs looked on as their mother swam off, thinking she was going to get some food

The pictures are from the Central Siberian Nature Reserve, and the mother is seen first gathering her cubs on the banks of the famous Yenisei River.

'There is a saying that a mother's instinct is never wrong, and these pictures capture the solemn moment a female bear bids farewell to the two cubs she has raised from birth,' reported The Siberian Times -'This is her final maternal duty, like a bird nudging her fledglings out of her nest, to send her children into the Siberian forest and taiga all alone.

'It is her conscious choice, or so it seems in these images.

'She does it in a clever way: choosing the Yenisei River bank for her last goodbye to her offspring, then surprising them by plunging alone into the cool waters and slowly but determinedly swimming across to the other side.

'It appears that she knows from intuition that her cubs - around one and a half years old - are still not strong and confident enough to swim across the river and follow her..... her scent will be gone forever.'

Eventually the cubs realised they had finally been abandoned and went searching for food

The cubs, at first confused, watch as their mother's ears poke out from the murky water, getting smaller and smaller.

Yet the young bears do not track her into the river.

They wait by the edge of the water, retreat for the night, and return the next day hoping to see her again.

Yet at some point they sense they are on their own.

The revealing photographs were taken by an unnamed veteran inspector from the giant nature reserve, in Krasnoyarsk region.

He reported that he had not previously witnessed the moment a mother bear judges her cubs are ready for their own lives.

'I've never before seen a bear family breaking up,' he said.

He was patrolling in the reserve when he noticed the family of brown bears on the point of a break-up.

'She had brought them to the bank of the Yenisei River,' he said.

'They stood together for a brief moment and then the mother went into the cold waters of the river, leaving her cubs behind.