A group of 3 cows would be called a "herd of cows". It is a very small herd, but it is technically a herd. Anytime you have a group of cattle it is called a herd.
A group of Crows is called a murder! I hope this helped! I don't know aboгt "Crows", but there is no any group like "predators". Basically we (people) can call this type of animals, which can kill...
Nobody knows for sure, but The Oxford English Dictionary suggests, the term "murder" maybe due to the crow's association with violent death, or to its raucous cry.