They are so determined even a lack of water cannot keep the birds from the 130-feet (40 metres) long, 40-feet (12 metres) wide pool. When zoo keepers first drained the pool for cleaning, the penguins simply jumped in and walked around the bottom, Tollini said.

"I'd like to think I know quite a bit when it comes to penguins but I am at a complete loss when it comes to this one," Tollini said. "The minute the six hit this pool, not only did they get in the pool and stay there, they convinced the other birds to do likewise."

Normally the penguins at the zoo's so-called Penguin Island spend this part of the year in their burrows, grooming, decorating their habitations and only occasionally waddling out for brief swims in the pool, she added.

KEEPER BECOMES A DRIVE-THROUGH RESTAURANT

That all changed with the arrival of six Magellan penguins formerly of Sea World in Ohio. Now the birds won't get out of the pool even to eat and no longer listen to Tollini who has names for all the birds and can tell them apart.

She said the constant swimming also makes it difficult to feed the animals. The penguins used to line up for food but now they just whiz by in the water, getting their food and vitamins on the go as Tollini dispenses food to the passing birds.

"I've lost complete control of the birds," Tollini said. "I am kind of like a drive-through restaurant now. they see me, see the fish, run past me, grab the fish and keep going."

While these types of penguins in the wild typically go on migrations of up to 2000 miles (3,219 kms) in search of food, these birds in captivity had never exhibited this type of behavior before.

Penguin experts say the birds are highly social and curious creatures and suggest the newcomers may have made such a splash that the others simply decided to follow.

"Usually there are one or two dominant birds," Ian Hiler, director of touring exhibits at Audubon Aquarium of the Americas in New Orleans, told the San Francisco Chronicle. "Somehow these animals came up and showed they are worthy of being followed."

For her part, penguin keeper Tollini predicts things will get back to normal in February when the onset of the breeding season will hopefully lure the birds back to their burrows.