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The Minnesota Zoo welcomed three Amur tiger cubs a month ago and the trio has successfully bonded with their mother, Sundari.

Sundari gave birth to four cubs on Mother's Day, though one died soon after birth, a Minnesota Zoo news release said. The two males and one female have been monitored over the last month and have reached several important milestones. They are being kept behind the scenes at the zoo.

"These cubs represent a major, positive step forward in our efforts to support the global population of Amur tigers," said John Frawley, Minnesota Zoo director. "Having three thriving cubs, and a mother who is successfully raising them, is a true testament to the care and dedication provided by our incredible team of zookeepers and veterinary staff."

Sundari, called Dari for short, has been a patient mother, zoo officials said in the release, and zookeepers' strong relationship with Dari has allowed them to perform routine health checks on the cubs.

The cubs were sired by Putin, a male tiger at the zoo who died in March. Dari and Putin are also parents to Vera, an Amur tiger born in 2017 that now lives at a Nebraska zoo, the release said.

The zoo has a long history with tigers. The first tigers came to the zoo more than 40 years ago. Before this latest litter, the zoo had seen 44 tiger cubs born.

The Amur tiger is a "top predator of far eastern Asia," according to the zoo's website. Amur tigers' numbers plummeted to 20 to 30 in the 1930s; biologists estimated there were about 360 left in the wild in 2005.

The cubs will be named in the coming weeks, zoo officials said.