Pictures of Heidi Montag Kissing Spencer Pratt on Her 24th Birthday

We celebrated Heidi Montag's big 24th birthday by looking back at her old bikini photo shoots, but she and her fellow animal lover, husband Spencer Pratt, spent their day bonding with wildlife at the Santa Barbara Zoo. They're back in the US following a stint in Costa Rica, and Heidi's still apparently adjusting to life back home. One thing's for sure — despite their plans to divorce, Heidi and Spencer were all about each other while touring the grounds between their kissing, hugging, and other PDA. It's hard to ever really know what's up with these two crazy kids, but click through to see how they spent Heidi's big day.