Auckland Zoo is dealing with the harsh reality of wild animals.

Sumatran tiger Zayana gave birth to her first two cubs on Friday.

But when the first was stillborn, she followed a natural instinct and killed the live second cub.

Carnivore team lead Lauren Booth says a tiger needs two to three cubs to make it worth raising them.

"The mortality rate within the first two years is about 50 to 70 percent. So there's a bit of maths that goes on there in terms of the resources they're going to put into those animals."

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