“They’ve really packed on some pounds, and you can see it in the contrast in the images when we look back,” said Ms Francis.
“It’s like different bears, it’s quite incredible.”
Shortly after arriving in June, the bears had smashed up part of their enclosure.
Ms Francis said: “Benji is definitely the naughty one out of the two, he’s broken and dug things up and been quite adventurous
“So it’s kept us on our toes, having to repair everything in his wake.
“Balu on the other hand is much more relaxed, he just sort of chills out in the background.”