Why the animals survived
This Slate article explains how the animals at Sri Lanka's national wildlife park at Yala survived the tsunami:

First, it's possible that the animals may have heard the quake before the tsunami hit land. The underwater rupture likely generated sound waves known as infrasound or infrasonic sound. These low tones can be created by hugely energetic events, like meteor strikes, volcanic eruptions, avalanches, and earthquakes. Humans can't hear infrasound—the lowest key on a piano is about the lowest tone the human ear can detect. But many animals—dogs, elephants, giraffes, hippos, tigers, pigeons, even cassowaries—can hear infrasound waves.

A second early-warning sign the animals might have sensed is ground vibration. In addition to spawning the tsunamis, Sunday's quake generated massive vibrational waves that spread out from the epicenter on the floor of the Indian Ocean's Bay of Bengal and traveled through the surface of the Earth. Known as Rayleigh waves (for Lord Rayleigh, who predicted their existence in 1885), these vibrations move through the ground like waves move on the surface of the ocean. They travel at 10 times the speed of sound. The waves would have reached Sri Lanka hours before the water hit.

How about us humans? Don't we hear those waves? We do. But, alas, the article says, we don't recognize them as danger signs:

Some people experience sensations of being spooked or even feeling religious in the presence of infrasound. We also experience Rayleigh waves via special sensors in our joints (called pacinian corpuscles), which exist just for that purpose. Sadly, it seems we don't pay attention to the information when we get it. Maybe we screen it out because there's so much going on before our eyes and in our ears.