Why do wolves live in packs? Most predators are like tigers, leopards, and weasels - they live solitary lives. Think about Kipling’s Sher Khan and expressions like lone wolves. Predators are the very symbols of solitariness. But wolves are different. They live in groups, called packs, comprised typically of 4 to 12 wolves.
It was long thought that wolves live in packs so they could kill their prey, like moose, which are much larger than wolves. But, Isle Royale wolves showed us that even a lone wolf can kill a moose. Later, it was thought that larger packs were more efficient at killing large prey. This also turned out to be not quite right. Decades of observations on Isle Royale wolves showed, quite surprisingly, that as pack size grows larger, each wolf in the pack gets less food. Although they kill moose a bit more frequently, larger packs have more mouths to feed.
We began to wonder, could ravens help us understand why wolves live in packs? Wolves are almost always followed by ravens - waiting to scavenge from the next kill. Typically, between 5 and 20 ravens attend a kill site. Each raven can eat or cache about two pounds of food per day. Ultimately, ravens can scavenge as much as a third of what wolves kill. Perhaps wolves live in groups to reduce losses to scavenging ravens. Larger packs, despite the cost of sharing with more pack mates, might do better than smaller packs by minimizing losses to scavenging ravens.
Assessing this idea, would require accounting for how all the costs and benefits of foraging change with pack size.
After a great deal of calculating and figuring, it seems that ravens offer wolves a reason to live in packs. It’s not what wolves kill that matters, but what they eat. Wolves living in larger packs lose less of what they kill to scavengers.
The red line is what wolves kill on a per wolf basis. The green line represents what each wolf get to eat (net energy gain, actually) when losses to ravens are taken into account.
When you catch something big, you must be prepared to deal with scavengers. Some species, like cougars, lions, and cheetahs hide the carcasses of their prey or cache them out of reach from scavengers.
Wolves have a different strategy. They eat fast. The faster a carcass is consumed, the less that is given to ravens. Wolves have two adaptations for fast eating.
First, wolves can consume a tremendous amount of food at one feeding. In just a couple of hours a large wolf can consume as much as nine kilograms (twenty pounds) of meat. This is why mothers invoke the wolf when asking their children to eat more slowly.
Second, wolves live in groups. The primary cost of group living is sharing food with pack mates. However, that loss is more than compensated by consuming food before ravens get it. Wolves that eat small prey are less vulnerable to scavengers, and are typically much less social.
So, is it important?
Science is important for discoveries that help us manage and control nature. However, discoveries like these about wolves and ravens, are valuable for a different reason. They reveal unexpected connections in nature. Awareness of such connections can inspire respect and wonder for nature. The importance of valuing nature in this way is under-appreciated.