As a blazing sun beat down on the city Tuesday, Rock Island — the moated exhibit at the Maryland Zoo in Baltimore where African penguins zip through cool, shallow waters — seemed a good place to be.

But the Druid Hill Park enclosure is nothing compared to the new digs planned for the zoo's prized colony of endangered birds.

In a move to further enhance what is already considered one of North America's most robust breeding grounds for African penguins, zoo officials started construction this week on a $10.4 million, 1.5-acre exhibit for the birds to call home.

Officials see the project, funded largely in recent years by consecutive state allocations of about $9 million, not only as a major investment in the future of the species but also as the first step in a "broad vision" to transform the nation's third-oldest zoo into one of its most modern.

"We think that this exhibit will redefine the zoo," said Don Hutchinson, the zoo's president and CEO. "People love penguins."

The black-and-white birds, each about 7 or 8 pounds, are quick and active, inclined to pull the shoelaces loose on a keeper's shoes as they waddle around their enclosure.

Pictures: Maryland Zoo penguins

"They definitely have their own personality," said Jen Kottyan, a former keeper who is now the zoo's avian collection manager.

The African penguin population in the wild, native to the coasts and islands of South Africa and Namibia, has been decimated during the last century by human consumption of their eggs, overfishing, coastal industry and oil spills.

The species' decline has escalated in recent years, according to Dyan deNapoli, a former penguin aquarist at the New England Aquarium in Boston who participated in a massive rescue of the birds in South Africa after an oil spill in 2000.

The wild population has dwindled from 165,000 in 2000 to an estimated 25,000 now, says deNapoli, who wrote a book about her rescue experiences and now lectures across the country about the species' plight.

The birds, now endangered, are the subject of intensive captive breeding efforts.

"The idea is, if we had to repopulate the wild, we're making sure that in the captive populations, we're maintaining extremely diverse genetics," deNapoli said.

Officials at the Maryland Zoo — which has had African penguins for a half-century — say their program is the single most successful breeding facility in North America, with nearly 1,000 chicks bred to date.

Kottyan says every African penguin colony in the country has some connection to Baltimore's bird colony.

Such signature programs define zoos in the broader zoological community, Hutchinson and others say. With the new, year-round exhibit underway, the zoo is poised to highlight in style what is already its crowning achievement.

The current 2,000-square-foot exhibit, a large structure of rocks that conceal a building surrounded by a concrete walkway and a broad moat, was built in the 1950s for mountain goats. It also housed chimpanzees before it was converted for penguins in the 1960s.

Today, its age is apparent, though the birds seem happy enough, as their breeding indicates.

The only access to the island is through a long tunnel that smells faintly of fish. The moat, which holds about 200,000 gallons of water, has no filtration system and must be drained and scrubbed clean once a week.

The planned 10,500-square-foot facility, which zoo officials want to open to the public in October 2014, will have a state-of-the-art filtration system that officials say will save about 7 million gallons of water per year.