ROYAL OAK, Mich. (AP) -- When penguins absolutely, positively have to arrive, The Detroit Zoo calls FedEx.

Officials said Tuesday the company delivered a flock of 20 earlier this month to the zoo in the Detroit suburb of Royal Oak from a California aquarium.

The aquatic birds have joined three other gentoo penguins that arrived earlier this year and await completion of their new home, the Polk Penguin Conservation Center.

The $29.5-million centre is scheduled to open in April and will be home to more than 80 penguins. The newest group of 10 males and 10 females are staying in a special quarantine area at the zoo's current home for penguins, the Penguinarium.

Once the new facility is completed, the Penguinarium will become a bat conservation centre.