Foraging is fundamental to the lives of animals. Without food, life is short and unproductive. As in other aspects of their lives, animals employ tacticss and strategies for finding their food. Choice of tactics is driven by the type of food and the defenses it presents. Strategies are probably best explained by optimal foraging theory, although this theory is controversial. Foraging in groups, or social foraging, is a key element for many animals; it may surprise you to learn that social foraging is not always the result of natural selection for cooperative behavior. Do the demands of foraging select for "intelligence" in certain animals? This question is interesting but difficult to answer.

"The wolves were very clever, the locals told the new arrivals. When one got into a pigsty, it would gently scratch and lick a pig, particularly behind its ears, to get the animal into a kind of pleasurable trance, so it would not make a noise. Then the wolf would lightly bite the pig on one ear and lead it out of the sty, all the time rubbing its body with its fluffy tail. The pig would still be dreaming of being caressed by a lover when the wolf pounced." from Wild Swans by Jung Chang (Touchstone, New York, 2003) p. 432. Whether truth or folklore, this tale gives insight into the complexities of foraging and the lengths to which animals go to secure a meal.

Foraging tactics

Both herbivores and carnivores employ specific srategies to bring them to their food. Generally a foraging animal exhibits several stages in its search for food. The first stage is a generalized search for appropriate habitat. For example, deer may have learned, or instinctively know, that richer forage is found near streams and rivers. Black-footed ferrets seek out prairie dog towns, where they will find their preferred prey. The second stage is a search strategy to find the actual food items. Searching strategies can be divided into two basic types:

Many carnvivores combine elements of these two strategies, so that an actively hunting animal may pause and wait when it encounters a likely spot to find prey. Herbivores are more likely to have to engage in continued active search until they locate an appropriate food plant.

Once food is discovered animals may that find hoarding is a beneficial component of foraging behavior. Hoarding takes many forms, ranging from territoriality, in which the animal drives competitors away from a food resource, to hiding food, to eating the competition. Hoarding allows an individual to conserve food for its offspring, group members, or for later consumption.

The final stage is consumption. This is simple for an herbivore, as once the right plant is found, it offers little or no further resistance to being consumed. Carnivores must subdue their prey before consumption, an often dangerous task that requires special skills and techniques.

Optimal foraging theory

Optimal foraging models attempt to predict the behavior of an animal while it searches for food, a nesting site, or other key niche components. The outcome of the models predicts both how individuals move in the environment and how individuals are distributed in the environment. Because foraging for food is the initiation of an interspecific interaction, optimal foraging models are frequently expanded and incorporated in population models that reflect the effects of herbivory, predation, or parasitism.

There are two important lines of investigation in optimal foraging: first, a more behaviorally-biassed subfield which investigates how animals make decisions, and second, a subfield that attempts to use the principles of optimal foraging theory to develop an understanding of dynamics at the population and community levels.

This area of behavioral ecology has been highly controversial because there are many reasons to believe that empirically animals either can't or don't optimize their foraging behavior. On a philosophical level, critics of optimal foraging theory have accused advocates of engaging in weaving ³just so stories² or of tautological reasoning, in which fitness gains are a self fulfilling prophecy of the models. Graysurveys a large number of experiments that test the theory and concludes that there is little empirical support for optimality models, particularly in ecologically complicated situations (and what in real life is not complicated).

Understanding foraging theory requires mastering:

Central place foraging is an important special case in which the foraging animal has a central place, such as a nest, to which it returns after foraging bouts.

Gray, R. D. 1987. Faith and foraging: a critique of the ³paradigm argument from design. in Foraging Behavior, A. C. Kamil, J. R. Krebs and H. R. Pulliam, eds. Plenum Press, New York

Social foraging

When two or more animals forage together, they are foraging socially. I'll divide social foraging into three distinct types, which are separated by the level of actual cooperation.

  1. Uninvited guests during foraging. These can be members of the same or different species. When one animal observes another eating, it is attracted and attempts to share the food. This behavior can lead to outright competition for food and to the loss of the food item by its original discoverer. For the discoverer, the problem is that to adequately defend the food may require so much time and energy that it does not get to eat. The animal must choose a balance between defense and consumption. For the guest, the advantages are numerous; it may get to eat without searching, and may avoid the risks involved in capturing and killing prey.
  2. Cooperative hunting. Animals may cooperate to trap elusive prey, or in taking down larger prey. While social bonds derived from kinship or mating may enhance cooperation, unrelated animals can also benefit from cooperation. An extreme example of unrelated animals cooperating to overwhelm a food item are pine bark beetles, which alone cannot overcome a tree's defenses, but in a mass attack can do so. More familiar examples of cooperative hunting involve felids (wild species of cats) and canids (wild species of dogs). Once the prey item is secured, competition for food among the hunters can be severe and may be regulated by dominance relationships in the group.
  3. Extreme cooperation in eusocial animals. In this case the foragers are sterile workers, which often have elaborate devices for communicating among themselves about the search for food. The difference, which is quite significant, between eusocial workers and other cooperative hunters is that competitive interactions for food among cooperators are minimized or absent; food is returned to the nest for allocation based on the colony's needs. Kinship is a key element underlying this level of cooperation.

Intelligence and foraging

How "smart" do you need to be in order to find your food? If intelligence is defined as problem-solving ability, insight learning, and memory, then most animals substitute what we might call "instinctive knowledge"--the genetically stored effects of generations of experience--for intelligence. However, intelligence, as defined here, serves an animal well if it is likely to face an environment that differs from its ancestors', or if during its lifetime its environment is likely to change unpredictably. Some scientists have argued that carnivorous lifestyles, such as those of felids and canids, select for problem-solving ability, insight learning, and memory in their foraging. Certainly many animals can change their strategy depending on previous foraging experience.

The other context which scientists have hypothesized as requiring "intelligence" is complex social communication. Because many animals combine social hunting, complex communication, and carnivory, it is difficult to discriminate among the selective forces that may have led to problem-solving ability, insight learning, and memory, in animals.

page 8-1
copyright ©2001 Michael D. Breed, all rights reserved