I'd have to say that shooting any big game animal with bird shot is very irresponsible to say the least! Very unethical and probably illegal too!
After taking a deer with buckshot, I won't even try buckshot again. If the animal goes down on the spot buckshot works. But since the pellets don't expand, if they run off, you will have a hard job finding them because most of the bleeding is internal. I don't know for sure, but I'd venture to say that bird shot for game animals is probably illegal in every state! It is not something that a "hunter" would use!