WELLINGTON • Once a rare sight in New Zealand's capital, the world's smallest penguins keep popping up in the central city - and that is not about to change.

A rogue pair picked up at a burger joint near Wellington's busy railway station on Sunday are likely the same birds that refused to give up their digs at a nearby sushi bar last month, Mr Brent Tandy from the Department of Conservation (DOC) told DPA yesterday.

Little blue penguins are known to be very tenacious, and like to return to the same location.

"It's possible that in the past, these birds have come up into the city to breed in a more stealthy site and weren't noticed," Mr Tandy said.

But it was equally likely that the birds were just trying out new nesting sites this year.

While the city is dangerous terrain for the aquatic flightless birds, the expanding penguin population in Wellington is good news for conservation, DOC science adviser Graeme Taylor said.

Nationwide, the number of the birds, which stand at an average of 33cm, has been decreasing, with some colonies going extinct.

But Wellington's penguin population has been thriving due to three harbour islands becoming safe havens - free from rats, mustelids, and feral cats and dogs that prey on the penguins.

The downside of the growing population is that the birds are not sticking to the harbour's edge when breeding.

"We will continue to see penguins in the heart of Wellington, near the harbour, as a few adventurous birds seek out new places to breed," Mr Taylor said.