Wisdom the albatross has laid another egg and is incubating it with her long-term partner Akeakamai, whose name means 'love of wisdom' in Hawaiian.

The albatross is at least 66 years old and still returning to her nesting site on the Midway Atoll National Wildlife Refuge on the tiny Sand Island, far to the north-west of the main Hawaiian islands.

Last year she successfully hatched a chick that scientists named Kūkini, Hawaiian for 'messenger'. She remains an active mother, and is thought to have flown a total of about 3 million miles or more in her lifetime.

Albatrosses mate for life, but Wisdom has outlived more than one partner. At 66 years old Wisdom is still a catch, and Akeakamai, her latest mate, is sharing egg-incubating duties with her. The pair take it in turns to sit on the egg, during which time they can't eat. After each turn the partners switch and the other goes off to feed at sea.

The egg, if it is viable, is expected to hatch in February 2017. Staff at the refuge will await the event eagerly. On the day that Wisdom was first seen with her latest egg, scientists at the research station were "abuzz with the news that Wisdom was back and incubating", Charlie Pelizza, US Fish and Wildlife Service acting project leader for the refuge, said in a statement.

Wisdom the albatross has laid another egg, thought to be her 41st. She is at least 66-years-old, scientists believe. USFWS Pacific Region

Age of Wisdom

Wisdom was first tagged in 1956.

Back then she was already breeding, so she had reached sexual maturity.

Albatrosses don't typically reach sexual maturity before about 5 or 6 years old.

So scientists' best guess is that Wisdom is at least 66 years old.

"I find it impressive that not only has Wisdom returned for over six decades as the oldest living, breeding bird in the wild, but also that biologists here on Midway have been keeping records that have allowed us to keep track of her over the years," Pelizza says.

The refuge is home to about 70% of the world's population of Laysan albatrosses. In December 2015 volunteers at the US Fish and Wildlife Service counted 470,000 active nests at the site. The breeding population is thought to be a little under 1 million birds.

In 2015, Wisdom successfully raised a chick with her long-term mate Akeakamai, who is hear pictured feeding last year's chick Kūkini. USFWS Pacific Region