FEEDING BEHAVIOR

Not one man in a billion, when taking his dinner, ever thinks of utility. He eats because the food tastes good and makes him want more. If you ask him why he should want to eat more of what tastes like that, instead of revering you as a philosopher he will probably laugh at you at for a fool
William James

General
Much of the behavior described in the preceding chapter is only indirectly related to the primary needs-those that must be satisfied if the animal is to survive for more than a few minutes, hour or days. The internal processes which determine that animals behave so as to satisfy these needs are sometimes called the homeostatic drives. They are set in motion by a departures from some internal state, such as the concentration of sodium ion in the body fluids, the amount of carbon dioxide in the blood or the temperature of the skin: for each of these there is a narrow range of values which a mammal tends to maintain.

This chapter deals with the activities which maintain a rat’s intake of food and water. The feeding of most animals is regulated by complex mechanism; but in studying an omnivorous mammal we are taking on the most difficult of the possible tasks. Omnivory, however, is not special to the genus, Rattus, or even to the family Muridae. Although the rodents are specialized. In their dentition and in head structure, for eating plant food, such as grains, many of those that have been studied closely have proved to be versatile feeders.

The voles of the genus, microtus , feed principally on the softer parts of rough grasses; but they readily take to roots, such as carrots or turnips; and they also eat grain. Apodemus and Clethrionomys , too, are adaptable feeders. Squirrel (Sciuridae) eat hard fruit and seeds, but also young shoots and buds, young bark , roots and even insect. Gerbils, such as Meriones, may eat land snails. In some conditions half the diet may be insect, especially termites.

Rats can also be predators on smaller mammals, birds and even fish. The factors which regulate feeding in natural conditions are almost unknown. Since we are principally concerned with the results of experimental analysis, we are obliged in this chapter to rely almost entirely on observations of laboratory rats.