https://www.goodreads.com/en/book/show/62008110-in-a-flight-...

"In this enchanting little book, celebrated physicist Giorgio Parisi guides us through his unorthodox yet exhilarating work, starting with investigating the principles of physics by observing the sophisticated flight patterns of starlings. Studying the movements of these birds, he has realized, proves an illuminating way into understanding complex systems of all kinds - collections of everything from atoms to planets to other animals like ourselves."

It comes naturally because you want to avoid a direct head wind. Granted it does not take the full shape of birds of fish, but on a 2-D level it is a similar process.

Granted, I am ignoring the impact of traffic and roads that are narrow. Without either I think a large group of cyclists will form a V pattern similar to geese.