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A Macaroni penguin carries a rock to build a nest with during the first day of breeding season at the Tennessee Aquarium's Ocean Journey exhibit on Monday.

Love is in the air at the Tennessee Aquarium's penguin exhibit.

The wooing is over and 18 penguin couples got down to business Monday morning with the arrival of several hundred pounds of the "magic rocks" the birds use to build their nests.

"They're busy as little bees in there running around and picking up rocks," said Senior Aviculturist Amy Graves.

But there's more to nest-building than just piling up pebbles. Penguins are picky decorators. Graves said the birds spend hours searching for the perfect rocks for their nests. And the quest for the right rock often leads to thievery.

"Many times they will go by piles of rocks ... to another bird's nest that might be out swimming, and they'll steal that rock," Graves said.

Graves said the birds rely on light to tell them when breeding season is on the way, and the exhibit's sophisticated lighting system has been telling the birds that breeding season is getting close.

Graves said once the birds sense the change, their appetites go through the roof.

"They want to look their very best and their plumpest for the breeding season," she said.

Of the exhibit's 26 penguins, 18 have formed pairs. Seven of the birds haven't quite reached full maturity yet, and one female is left without a partner.

The season lasts until all the chicks have grown their tuxedo-like black and white feathers and "the last chick is safely swimming," which is typically around September or October.