Rosie, a Humboldt penguin, arrived at Sewerby Hall and Gardens near Bridlington in 1990 and has already outlived others of her breed by more than a decade.
Her 30th had to be celebrated behind closed doors, but with the zoo open again, visitors will be able to see Rosie on the big day.
Head zookeeper John Pickering knows Rosie better than most - he picked her up from Birdworld in Surrey when she was just three months old and he was 28.
Her 30th was celebrated with a watermelon studded with sprats which she could pick out and it's likely she will get a similar treat on Tuesday.
Mr Pickering said she suffers from arthritis now and walks slower on land, but pain relief - given in a sprat - helps.
For many years she was partnered with a penguin called Dion, who has since died.
They were called Dion and Rosie because of a song by the American singer songwriter Dion DeMucci whose song The Wanderer has the line: "I tear open my shirt I got Rosie on my chest".
Mr Pickering explained: "When we first got Rosie and Dion as juveniles they were a bit mischievous and would climb over a short rocky wall and escape from the enclosure and go into the waterfall pond and I used to get a phone call from security saying your penguins are out again."
Mr Pickering, who likes 50s music, mentioned what had happened to someone, who said they were wanderers - giving him the idea for their names.
Dion died a few years ago, so now Rosie lives with one of the three chicks she's had over the years called Flip Flop - they live together in a small hut.
Now Rosie is getting on, she's hand fed so she doesn't have to compete with the younger birds.
Unlike some of the others she never snatches her food. "She has always been gentle," said Mr Pickering. "It is almost like there's no bad bone in her body."
As for her much longer she will live, no one knows.
He said: "The only worrying thing is the arthritis - obviously we have to monitor that and make sure she is not in too much pain. We wouldn't want her to carry on if she is suffering.
"At the moment she is fine, she has a great appetite and she swims brilliantly in the water."
An audience of up to 10m saw her birthday last year after it was featured on CBS News and ABC News in the USA, as well as Good Morning America.
He said: "It was on a couple of stations in the States, Hawaii, to Australia and even Russia, it was crazy. I think everybody loves animals - the longevity to get to that age.
"It came at a time when the only other news was coronavirus and this was a bit of light entertainment."