SAN DIEGO (CBS 8) - On Thursday, SeaWorld celebrated "Rock Day" at the penguin encounter. There was no music, but there were rocks. 

"Rock Day" is the kick-off to the penguin's breeding season that  begins this month and last until January. 

About 14 tons of mesquite river rocks were brought into the Penguin Encounter. 

Instincts immediately kicked in and the birds began to pick up rocks and build bowl-shaped nests.