There are several people on here that have had this very experience, and they were told to calculate potential loss value due to the fact that they are livestock and are animals specifically utilized for production. Some were even told this by their local authorities governing these particular situations. Laws are different everywhere, though, and in some places there isn't a precendence for this type of situation, and what to do about assigning value to the birds is up for interpretation. Some of the people in this situation have also included the cost of feed, bedding, vet bills (if any were incurred), cost of care for remaining live birds, damage to the coop/property that the chickens were on ie if they got into the coop by chewing or knawing it. It can also heavily depend on what your birds were for. Were they primarily for production purposes for you business(for eggs breeding etc?) If so the potential loss calculation is a viable one for sure. If they were pets that laid eggs for you the potential loss is still viable, but you're not always as likely to get compensation for potential loss then.
Hopefully someone with actual experience in this can come along and tell you the specifics of what they did. I lost my first chickens in the summer due to the neighbors dogs, but due to their willingness to pen them, and the fact that we were brand new to the neighborhood and didn't want to start off on the wrong foot, I decided not to pursue compensation. We have an agreement though now, that if their dogs are seen on our property, we will have to shoot them, since once a dog eats a chicken, they have a taste for it that is rarely extinguishable.
You might do a search on here and see if you can find some threads on this. I know they're there b/c there were a BUNCH of dog attacks this summer, with info pertaining to what you're looking for.
Good luck, and sorry for your loss.
