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Chewing incidents on different substances.
After Day et al., 1996.

They found that when pigs were given unlimited food, there was no significant difference in tube preference. However, pigs whose food intake was reduced had a significant preference for saccharin over water and sucrose over saccharin. Pigs whose food intake was limited spent more time chewing the tubes than pigs on the high feeding level schedule. This indicates that some chewing activities were motivated by hunger. However, the substantial amount of time pigs spent chewing the water tube suggests that chewing is also an exploratory behavior. The researchers concluded that young pigs chew to gain information. Taste and nutrition serve as feedback to promote chewing particular materials so that the pig obtains proper nutrition. (Day et al., 1996).

How can an animal’s behavior be explained?

Causes of animal behavior can be divided into two broad categories: proximate causes and ultimate causes. Questions about proximate causes ask how a behavior occurs while questions about ultimate causes ask why it occurs. Proximate causes involve the immediate condition of an animal that allows it to behave the way it does, including its development and physiology. For example, as noted above, pigs exhibit more stereotypies when they are hungry versus when they are sated. A simple proximate explanation for this might involve low blood sugar triggering the activation of certain genes that code for hormones that make the pig feel hungry and signal the brain to stimulate jaw muscles to bite or chew. Alternatively, ultimate explanations examine how a behavior evolved over time. An ultimate explanation for increased stereotypic behavior in hungry pigs would involve how this would contribute to the pigs’ fitness. For instance, hungry pigs chewing nearly anything they can find may have a better chance at finding food than hungry pigs that only exhibit foraging-like behaviors when they are sure they have encountered food. Pigs chewing inedible material would thus be less prone to starvation and more fit. Genes for this behaviors would be selected for, and stereotypies would result.

Summary

Pigs were domesticated from the wild boar over 8,000 years ago, but few behavioral differences between the species have been noted. Both species are called Sus scrofa . Domestic pigs are sometimes referred to as Sus scrofa domesticus . In the process of domestication, humans control which animals reproduce and animals adapt to their given environment. Artificial selection occurs when humans select for particular traits by allowing animals with those traits to breed.

Optimal foraging theory examines how animals make foraging decisions. It argues that animals forage in such a way as to maximize their caloric intake while minimizing energetic costs. Domestic pigs and wild boars use similar foraging strategies that follow the predictions of optimal foraging theory. For example, they spend more time in one area containing food when energetic costs to move to another area increase. Crossbred pigs use a costlier strategy that involves moving between areas with food more often. That is, they expend more energy when foraging than domestic pigs do. This is likely because vigilance as a means of protection against predators is selected for in wild animals but not domestic ones. Aggression between pigs increases as distance between food sites decreases because pigs move between sites more frequently and subordinate pigs have less time to escape an approaching dominant pig. Domestic and feral pigs follow a producer-scrounger model in which subordinate pigs find food and eat what they can before dominant pigs prevent them from eating more. Foraging is such an important behavior for pigs that even in captivity when unlimited food is available, they will display foraging-like behaviors like rooting in the dirt and biting and chewing inedible materials.

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Source:  OpenStax, Mockingbird tales: readings in animal behavior. OpenStax CNX. Jan 12, 2011 Download for free at http://cnx.org/content/col11211/1.5
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