Family dining, carnivore style

We have now officially entered the holiday season. This means that most people will spend much time/money/energy traveling to various corners of the country with one main objective: large meals with family members. Many holiday traditions, not just the Judeo-Christian ones most commonly celebrated in the U.S., involve some variation of a group gathering with traditional/ceremonial foods. These events can be an important way to solidify bonds and pass on stories, information, and tradition from older to younger generations.

Although holiday meal gatherings are an important way to spend time (either voluntary or otherwise) with family members that you may only see a few times a year, there is usually at least some stress and tension underlying even the most Rockwell-esque of gatherings. Children pick on each other, adults pick on each other, someone always ends up sulking because someone else snapped at them. Sound familiar? The truth is that the holidays are usually pretty high stress, and many people's gatherings bear a closer resemblance to the Griswalds than the Rockwells.

Well, other mammals aren't all that different. Social carnivores often hunt in groups, and often times many other group members that did not participate in the hunt join in when the time comes to chow down on the carcass. Feeding privileges are largely according to rank, but there is usually some squabbling and jostling, and frequently some members of the group come away distinctly unsatisfied. Beyond the typical grumpiness of hungry animals, however, how does eating as a group affect foraging efficiency?

Even though a group can bring down larger prey, the amount of food per animal often actually decreases when carnivores hunt cooperatively instead of individually. Packer et al (1990) found that for lions there is an optimal hunting group size of about 5 or 6 individuals. In bigger groups, there is so little food per lion that it isn't really worth the kill, so even in large prides members will break up into smaller groups to hunt.
There is a catch, though. The study showed that females hunting alone actually are able to obtain just as much food as females hunting in quintets. Why, then, bother with the buddy system? A lion can gain just as much if she forages alone, so why hunt in groups when it means less net food per stomach?

As is common with many problems, looking at exceptions to the rule can provide important clues. It turns out that members of small prides will actually hunt in larger than optimal group sizes. Why would members of small prides sacrifice efficiency, when members of large prides break up into groups?

Kills do not occur in a vacuum. Most areas of Africa are home to many sympatric carnivores and scavengers, and kleptoparasitism is a major issue. Smaller groups of lions are less able to defend their kills, and run the risk of a large pride coming across their meal and taking it over. They also need to defend their offspring from infanticide by members of other prides, and so they tend to aggregate in larger than optimal foraging groups, in contrast to members of larger prides that have more members available to tend cub creches and hunt. So, for lions the importance of "strength in numbers" to defend both food and cubs results in foraging groups that aren't sized correctly for optimum hunting efficiency.

Lions are not the only example of trade-offs involved in group size. One of my all-time favorite carnivores is the African wild dog (Lycaon pictus), and members of this species are also group hunters. Larger groups are, again, able to take down larger prey, but the per capita amount of meat still does not always rise accordingly. Creel (1997), however showed that there is more to the picture than just the amount of meat taken down. Apparently larger groups not only take down larger prey but also travel less distance to do so. The important factor is not the calories of food obtained per dog, but the net calorie intake, which takes into account the energy used in the hunt. Wild dogs are subject to even more kleptoparasitism risk than lions, and larger groups are able to defend prey better than small ones, providing another way to increase net energy from a hunt. On a slightly unrelated note, wild dogs are also interesting because pups get priority at a carcass (Schaller 1972), in contrast to lion society, where cubs are low-ranking and are often among the last to feed at a kill.


So, whether you enjoy your family gatherings this year or just endure, remember that you are not the only mammal dealing with mealtime tensions! Maybe we should look for a positive moral from this story: although large meal gatherings can result in stress and sometimes conflict, most mammals do derive ultimate benefit from extended family groups, even if it takes some compromise. There are many more interesting factors involved in the determination of optimal group size (kin selection, including alloparental care, is often a big factor in social structure, and ecological context/resource distribution is important as well), the two papers cited below are great resources if you're interested in the topic.


Creel, S. 1997. Cooperative hunting and group size: assumptions and currencies. Animal Behaviour. 54: 1319-1324.

Packer, C., D. Scheel, and A. Pusey. 1990. Why lions form groups: When food is not enough. The American Naturalist. 136: 1-19.

Schaller, G.B. 1972. The Serengeti Lion. Univ. Chicago Press, Chicago, IL, USA.

(Photo credit for lions, wild dogs 1 and wild dogs 2)