If you've never seen a murmuration of starlings, there are some spectacular pictures on this BBC page. A murmuration is a flock, but it only refers to starlings. Other birds have other words to describe the same thing: a murder of crows, an exaltation of larks, or a walk of snipes, for instance.
These words sound rather quaint and age-old, but in fact, they only gained currency in the 20th, occasionally the 19th, century. They appeared in some hunting and falconry glossaries of the 15th and 16th centuries, but appear not to have been known more widely. The OED has two citations for murmuration from the 15th century, then there is nothing until 1932. Exaltation has a citation from 1430, then the next one is 1824. Citations for murder, as in a murder of crows, jump from 1478 to 1939, for peep (of chickens) jump from 1486 to 1975, and for muster (of peacocks) jump from 1450 to 1696 (although this was a dictionary, and may have repeated something from an older source) to 1820. Other such collective nouns from the period include a badling of ducks (or hens), a labour of moles, a rag (or rage or rake) of colts, and a richesse of pine martens.
Two of the frequently mentioned 15th century books from where the citations come are The Book of St Albans and Lydgate's Horse, Goose and Sheep.
These collective nouns, coined in the Middle English period, do not refer only to birds and animals. They were clearly invented with jocular intent. The OED also has a rascal of boys, a misbelief of painters, a never-thriving of jugglers, a melody of harpers (harpists), a poverty of pipers, a faith of merchants, a laughter of ostlers, a safeguard of porters, a discreetness (or discretion) of priests, a prudence of vicars, a superfluity of nuns, and a non-patience of wives.
Such words are known as group terms, collective nouns, or terms of venery. See this old post entitles Terms of venery for more on their origin.