1-10. HABITS AND BEHAVIOR
a. Reaction to Strange Objects.
(1) Rats very often carefully avoid strange objects, even strange food. Since
strange objects may be dangerous or even deadly, it is to the rodent's advantage to
investigate them very cautiously. This "strange-object" reaction has led to many stories
about the "wily" and "highly intelligent" rat. The answer is a great number of these
stories is that the rat recognized the trap only as a strange object to be avoided, not
specifically as a trap. Probably one of the reasons that the last few rats or mice in a
building are so difficult to kill is that these survivors have the strongest reaction to
strange objects. Hence, they avoid all new attempts to kill them. Mice, on the other
hand, are naturally curious (especially the males). They will actively explore any
change to their environment.
(2) Several studies have been made which show the effect of strange objects
in the rodent's environment. During experiments with wild Norway and roof rats,
changing the design of the feeding tray was enough to cause feeding to drop almost to
nothing. This reaction would sometimes persist for several nights. Lights left on at
night in a normally dark room, or unfamiliar noises, also caused a decided drop in
feeding. Even changing the location of a familiar object caused avoidance and a
lowering of general activity. On the other hand, complete removal of a familiar object
commonly had no effect, even to the extent that rats ran around the place where the
object had been rather than taking the shorter route opened to them by removal of the
object. These studies also point out that rats may avoid new food for several days.
This is an important fact in poisoning operations. When the rat first begins to take a
new food, it may only take "token" amounts. If these amounts contain a sublethal dose
of poison, they may make the animal sick and thus strengthen the avoidance reaction.
This is the biologic basis for the use of unpoisoned bait, or prebaiting, before the poison
is added. The feeding studies also indicate that hunger causes the avoidance of
strange objects to break down more quickly.
(3) In environments where "strange objects" appear regularly, however, rats
and mice may show little or no evidence of the avoidance reaction. This is particularly
true in such places as in warehouses where a constant turnover in harborage and food
is occurring. Rats feeding on garbage are accustomed to new foods and may accept
b. Climbing. One should not underestimate the climbing ability of rats and
mice. Roof rats and house mice are notoriously good climbers, and other rats can climb
very well if they have to. They can climb the vertical walls of most brick buildings or any
vertical surface where they can get a toenail hold. Nailheads or screwheads placed too
close together can serve as steps for rodents to climb. Smooth surfaces can be
climbed if there is a pipe, a corner, or something else against which they can brace their
backs. Vine-covered walls are perfect runways, and since the vines afford
concealment, they can be used by day or night. It is well to remember that rats and