Peaceful Mobs always spawn in groups of four

When I loaded up A new Minecraft world in 1.10, I started flying around to look for a specific biome. On the way, I noticed that all of the passive mobs that I passed all spawned in groups of 4. I know that they sometimes do this naturally, but it happened every single time that I saw a peaceful mob. I repeated this, creating a few new worlds and all had the same result.