Random #Wikipedia browsing brought me to this: wild horses.

Wild horses live in herds with a social hierarchy, formed by a dominant adult male or sometimes multiple males (harem stallions), as well as several mares and their offspring. The harem stallion aggressively defends his herd/harem against rival males.

Sure, that’s about what you’d expect.

Upon reaching adulthood, both male and female horses disperse to other herds to avoid inbreeding, with young adult males also forming bachelor groups when they are around 3 years of age. In bachelor groups male horses engage in play and ritual behavior, with the group forming a hierarchy.

…apparently wild horses have frats.

(To be fair, the frat bros I knew in college behaved pretty much like wild horses, so this may not be the revelation I think it is.)