Pack size is highly variable and fluid because of the birth of pups, dispersal, and mortality. Prey availability and size are also factors. Where prey animals are smaller, packs are often small. Where prey is large, the packs may be larger. For example, in Alaska and northwestern Canada some packs reportedly have over 20 members. One pack (Druid Peak pack) in Yellowstone National Park once swelled to over 30 members, but this is highly unusual and not necessarily an advantage. More pack members means more food must be obtained. Wolf packs are generally largest in late autumn when the nearly-grown pups are strong enough to hunt with the adults. Over the winter months, some wolves may disperse to find mates and territories of their own. Others die, and by spring, before the arrival of a new crop of pups, the pack size has often diminished. Red wolf packs are generally smaller than gray wolf packs and usually have 2 to 8 members, but a pack of 12 has been observed in the wild.