It's weird. Sometimes animals on the screen trigger our dogs to watch, and sometimes not. I've never been able to figure out what in particular grabs their interest. I do know a cryong puppy will make them look and listen, but the soon figure out it's the TV and lose interest...
My cocker spaniel barks at animals on TV, especially horses. The dinosaurs in the Jurassic Park related commercials drive her utterly insane. Dog logic: barking works because the dinosaurs stay in the TV and don't invade the house.