mice do not climb at every opportunity. They work only as hard as is necessary, and
only when they are driven by hunger or lack of shelter will they try the feats mentioned
c. Jumping and Reaching. Rats can reach as much as 13 inches along
smooth vertical walls; therefore, a safety factor must be added to rat guards to make
certain that the rodents do not pass. The distance that should be completely clear of
possible holding points is 18 inches. Rats can be expected to make a standing high
jump of nearly 2 feet. With a running start and a bounce against the vertical surface
two-thirds of the way to give them a boost, rats can jump a little more than 3 feet.
Under these conditions, even the much smaller house mouse can jump more than 2
feet high. Jumping out and down from a height of 15 feet, a rat can cover a horizontal
distance of 8 feet. It can do even better with a running start.
d. Swimming. All three of the commensal rodents are good swimmers. This is
especially true of rats, and they have been known to swim as much as one-half mile in
open water and tread water for three days. If young rats are placed in a tank, they will
swim readily. There are reports that rats swim up through floor drains without
hesitation. In many large cities, rats use the older sewer systems as regular highways.
They can survive being flushed down a toilet and re-enter the building by the same
route. Anyone responsible for ratproofing inspection should be familiar with the layout
of the major sewer lines in the area to be ratproofed. Information is especially important
on small trunk lines that were abandoned but not removed when larger mains were laid.
This is very important in cities where the first sewers were made of wood.
e. Nesting and Harborage.
(1) Rats and mice will nest wherever safety can be found close enough to
food and water. Holes or burrows in the ground may be used for hiding and nesting
outdoors. In buildings, rats and mice use double walls, the space between floors and
ceilings, closed-in spaces around counters, or any place hidden from view that enemies
cannot reach. Generally, rats and mice build their nests in hiding places that are
relatively quiet. They gather whatever soft material is nearby, or tear up paper and cloth
to line the nest. Rat nests generally are bowl-shaped and about 8 inches in diameter.
Occasionally, they are completely roofed over. Mouse nests are similar to rat nests but
are smaller, about 5 inches in diameter. Normally, they are covered, and entrance is
through a small hole in one side.
(2) In addition to disclosing nesting sites, a careful search may reveal hidden
resting and feeding stations. These are places safe from enemies where rats and mice
can eat or rest undisturbed and are usually found somewhere between the food supply
and the nest or burrow entrance. To these spots, the mice and rats carry or drag food,
and they leave behind feces, food wrappings, and scraps. The ideal condition, of
course, is where harborage is such that runways, too, can be concealed. Too often this
condition is found around man's dwellings and business places.