After emptying a bucket of rock inside the penguin exhibit at the Tennessee Aquarium Thursday morning, April 2, 2015, Holly Lutz, left, animal trainer and presenter, returns for a refill passing "Little Debbie, " near right, as she begins her nest building.

The penguins are eager.

They begin screeching with excitement as the first bucket of rocks is dumped inside their home in the Penguins' Rock exhibit at the Tennessee Aquarium on Thursday morning.

"These are like magic rocks that signal breeding season," said Loribeth Lee, senior aviculturist at the aquarium. "They have a one-track mind, and breeding is all they can think about."

Once a year, typically during the first week of April, aquarium staffers begin to haul more than 500 pounds of rocks into the exhibit for the penguins to use to build their nests. The rocks they bring in are specially selected: they need to be small enough for penguins to carry in their beaks, but not so small they can be swallowed, Lee said.

During the breeding season, penguins are noticeably more aggressive, Lee said. They occasionally get into fights over rocks and each other's nests.

As soon as the nests begin to take shape, the penguins will start to select their partners for the mating season. The aquarium's exhibit is home to two breeds of penguins, macaronis and gentoos. Both breeds will mate only with their own kind, and the couples will remain together throughout the breeding season.

some text
Teresa Eisenhardt, left, Amanda Eisenhardt and Lauren Smith react as they watch penguins begin nest building with rock Thursday, April 2, 2015, inside the Tennessee Aquarium.

This year there are 19 penguins of breeding age.

"This means one female is going to be left out," Lee said. "We don't really know who will end up together."

Aquarium staff anticipate having about 14 eggs, but Lee said it's normal to only have a handful of chicks hatch. Once the eggs hatch, the chicks will stay under the protection of their parents for 10 weeks, hardly moving.

Hunter Hays, 12, was visiting the aquarium on Thursday with his family. He and his younger brother stood at the glass walls of the exhibit and watched as the penguins frantically carried rocks in their beaks.

"It's really cool seeing how the penguins build their nests," he said. "But I don't think I want a penguin for a pet. I bet they could get annoying and would be kind of loud."

Contact staff writer Kendi Anderson at or at 423-757-6592.