If the strength of the wolf is the pack, it makes sense that wolves have evolved to live in large groups. Between 1995 and 2015, Yellowstone packs averaged 9.8 wolves and frequently grew to 20, with the largest pack recorded at 37 members. But living in such a large family isn't always beneficial to other aspects of wolf life. The most efficient pack size for successful elk hunting is only four wolves (MacNulty et al. 2012) and eight for reproduction (Stahler et al. 2013). Living in a large group often means each individual wolf gets less to eat (Schmidt and Mech 1997). The largest packs tend to exhibit more fission-fusion behavior (Metz et al. 2011), much like chimpanzees and hyenas (Lehmann and Boesch 2004, Smith et al. 2008). They may be able to get away with being less cohesive because when they break into smaller groups, each wolf gets more food; and as long as each group is larger than its neighbor's full size, it is still likely to win in a territorial contest.