Yun Zi (pronounced yoon zah), a male giant panda, checked out his birthday cake this morning at the San Diego Zoo. The birthday boy turned four years old today and received an elaborate four-foot-tall ice cake, topped with a big ice "4" and filled with some of his favorite treats – apples and yams. Yun Zi's celebration came just one week after his brother, Xiao Liwu (pronounced sshyaoww lee woo), celebrated his first birthday at the Zoo.