The ice-cold nursery is getting a little more crowded.

Two additional penguin couples have laid eggs at the Tennessee Aquarium.

Paulie and Chaos, macaroni penguins, were the first birds to produce an egg at the Tennessee Aquarium’s Penguins’ Rock exhibit, laying one in mid-May. Two pairs of gentoo penguins now are tending eggs of their own and there should be another egg by the end of this week, spokesman Thom Benson said.

“Gentoo penguins will keep both of their eggs in the nest as long as there is enough food and there aren’t many predators,” said Tennessee Aquarium senior aviculturist Amy Graves.

Ms. Graves discovered the first gentoo egg in Bug’s and Big T’s nest on Saturday and a second egg was found Tuesday morning. On Monday, an egg was discovered in Biscuit’s and Blue’s nest.

If their eggs are fertile, Bug and Big T could be first-time parents. Biscuit and Blue, who are more mature, came to the aquarium as a pair and have had chicks at another facility, the aquarium reported.

The incubation period for macaroni penguins takes 33 and 39 days, so if Chaos and Paulie’s egg is fertile, a chick could begin to “pip,” or hatch, between June 15 and June 23.

The incubation period for gentoo penguins takes 36 to 41 days, so keepers must wait until sometime in mid-July to see if the newly discovered gentoo eggs are fertile.