Kevin recently visited five gentoo rookeries on an Aquarium trip to Antarctica and noticed the nesting rocks were similar to limestone that's quarried around Chattanooga. This photo was taken in Antarctica by Jack McKee. It shows a gentoo on a nest that is built up out of these angular rocks.
Last year smooth, rounded river rocks were given to the Tennessee Aquarium's penguins for nesting material. The birds built nests, but as Amy Graves explained, "When the penguins would lay down on the nests, some of the rocks would slide out. Especially when the big gentoos would lay down." These more jagged and angular rocks should allow the Aquarium's birds to build taller nests similar to the ones Calhoon observed in Antarctica.
The individual rocks were carefully hand selected by the group as seen in these pictures. The rocks couldn't be small enough for any of the birds to swallow, or too large for the penguins to carry around in their beaks.
Kevin probably wished he had Fred Flinstone's brontosaurus crane to load the rocks. They gathered nearly 1,000 pounds of rocks for the penguins!