One of the interesting and quirky things about the English language is the phenomenon of collective nouns for groups of animals. The tradition of using terms of venery, or hunting, stems from the English hunting tradition of the late Middle Ages. The whole hunting tradition was originally adopted from the French and gave rise to an extensive specialist vocabulary. In the course of the 14th century, it became a courtly fashion to extend the vocabulary, and by the 15th century, this tendency had reached exaggerated proportions. For instance, The Venerie of Twiti, a book from the early 14th century, distinguished three types of droppings of animals, and three different terms for herds of animals. The focus on collective terms for groups of animals emerges in the later 15th century. A list of collective nouns in a manuscript dated to c. 1452 extends to 70 items under the heading of termis of venery &c. The list in the Book of Saint Albans (1486) contains 165 items, many of which relate to groups of people and are clearly humorous: (a Doctryne of doctoris, a Sentence of Juges, a Fightyng of beggers, an uncredibilite of Cocoldis, a Melody of harpers, a Gagle of women, a Disworship of Scottis etc.)
Many of the collective nouns we know today are made up and usage, other than in compiled lists, is difficult to find. Sometimes a collective noun may have been invented as a joke, but as it referred to something of the essence of the animal it gained popularity and was accepted as a proper term. I fancy that a ‘murder’ of crows is an example. The book A Conspiracy of Ravens is a list of collective nouns for birds. It was compiled by Samuel Fanous, with illustrations from the English engraver and natural historian Thomas Bewick (1753-1828).
Our cats would be in complete agreement with the collective noun for a group of Magpies that features in this book. Some years ago one of them caught and killed a fledgling Magpie. Ever since then there are a couple of Magpies that wage a war on them in spring and summer. The cats get screeched at and dive bombed by them when they go out into the garden. Even when they are inside, on the back of the sofa, looking out, they are attacked. The magpies sit on the satellite dish and screech at them. Even Harris, who is a fine specimen of a cat, a bruiser that seems to be able to take on any other animal, is cowed by them.