Zombie Animals

We talked about zombie animals at one point but not too far in depth, and the topic was dismissed. However, I've been thinking about it recently and have decided it would be an interesting addition to the story. Too keep it from being too ridiculous and destructive I thought of a couple "rules" per say to balance things out.

• Zombies are only interested in human blood, therefore do not attack animals to infect them.
  
• Animals contract the virus through eating flesh of infected, either 'alive' or fairly recently killed.
  
• Zombie animals tend to stay in groups
  

With these rules, the main factor of what we couldn't do much about, Birds, wouldn't be so crippling. Only certain types of birds would eat dead flesh such as crows. They would travel in large groups, which would be very loud as there are bound to be at least a few crowing constantly making us aware. It would be an interesting factor if we were to have to hide inside or under brush, etc. due to birds.