The Beardsley Zoo is preparing to celebrate the first birthdays of two rare tiger cubs whose survival was not a given.

The Bridgeport Zoo's rare Amur tiger cubs Reka and Zeya now weigh 170 pounds and are still growing. That's a far cry from their birth weight of about 2 pounds.

The sisters' births made headlines since their species is critically endangered. There are only 400-500 Amur tigers living in the wild.

The cubs almost didn't make it after their mother rejected them. Zoo staff had to step in and pull them from their habitat and hand-rear them for months.

The duo is only two of four cubs born in zoos in North America this year who have survived.

"It's a good mark because at first we were going day-to-day and then week-to-week, (saying) 'Are they going to make it?'" says animal care specialist Chris Barker. "But now at a year old, it's a whole lot of relief."

The zoo is inviting the public to celebrate their special day this Sunday with a party. The celebration will include cake, hot chocolate, presentations describing how the cubs were raised and special enrichment gifts for the cubs.

Zoo staff also say they are planning to make a special announcement.