One of the three endangered Amur tiger cubs born at Toronto Zoo last week died yesterday.

According to a tweet this afternoon from the zoo, it had started looking sickly early Friday morning, and its mother, 14-year-old Mazyria, separated it from her two healthier cubs.

Zoo staff rushed in to see if they could save the 790-gram kit, which was dangerously cold and severely dehydrated.

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The team made heroic efforts, including inserting a stomach tube to feed the cub, who had not yet learned to suckle.

The cub improved long enough to undergo an examination, and an ultrasound revealed the underlying cause of its mother’s initial rejection. They found evidence of hepatitis, which had damaged its liver beyond repair.

The veterinary team gave the cub a little stuffed toy with a heartbeat to cuddle, and as its condition worsened, they decided to end its suffering late Sunday evening.

After a very difficult weekend of valiant efforts from the Wildlife Heath and Wildlife Care teams, we are saddened to announce that we said goodbye to one of Amur tiger Mazy’s cubs on Sunday, May 9, 2021. https://t.co/l6ixje9Q3B pic.twitter.com/GRquYdy30H

— The Toronto Zoo (@TheTorontoZoo) May 10, 2021

Its two siblings are doing well, with no evidence of a similar condition.

Amur tigers, also known as Siberian tigers, were hunted nearly to extinction in the 1930s, when there were as few as 20 of them left on the planet. They were recently promoted from critical endangered to merely endangered, in part as the result of breeding programs like the Toronto Zoo's, which paired Mazy with Vasili, who was born at the Calgary Zoo.

There are still estimated to be fewer than 500 Amur tigers left in the wild. If all goes well from here, the two surviving cubs will be the 21st and 22nd raised at the Toronto Zoo.