Aurora, one of the zoo's two female polar bears, gave birth to three male cubs on Nov. 9 but despite her efforts at nursing them, zoo staff say two did not survive the first 48 hours.
The remaining cub was taken from Aurora on Nov. 11 after staff noticed he wasn't moving as strongly as before, and he was transferred to the zoo's intensive care unit weighing less than 700 grams.
A team of veterinary and wildlife care experts have since been monitoring the cub's temperature, taking blood samples, weighing him and feeding him a special formula to help build up his strength.
The zoo says the surviving cub continues to grow stronger each day, and is becoming more active and asserting his personality by growling and calling to staff.
The cub remains in a temperature-controlled environment and enjoys seven feedings a day, each followed by an exercise session to help his growth and development.
The zoo says the cub's eyes will not open until 40 days after birth, but his coat is gradually becoming thicker and several other milestones have been passed.
He began showing his contentment by purring on Nov. 15, began crawling on Nov. 17 and rolled over for the first time on Nov. 23.
"While it still remains day-to-day with a cub so young, the team remains hopeful with this small survivor," the zoo said in an update Thursday.