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Black Rat (Roof Rat, Ship Rat)
Rattus rattus have a uniformly colored dorsal side, usually black to
tawny brown. The underbody is paler, lighter brown or slate colored.
The tail is longer than the head and body, sparsely haired and
scaled. These rats are typically 18-22 cm long, with a
tail approximately 18.5-24 cm in length. Adapted for climbing and
living in high places, the feet retain all of the digits, with a
rudimentary pollex.
Reproduction
Rattus rattus have a high reproductive potential. The breeding
season lasts all year. Under normal conditions, females have between
three and seven litters per year. The average litter size is between
six and twenty-two young. The gestation period lasts
twenty-two days in nonlactating females and twenty-three to
twenty-nine days in lactating females. Young weigh four
to five grams at birth, and are born blind, naked, helpless, and
wholly dependent on the parent for several days. The young open
their eyes around the fifteenth day of life. Weaning occurs at three
to four weeks. Sexual maturity is
reached at about eighty days.
Behavior
The black rat is active at dusk and during the night.
Having a history of dependence on man, living in human communities,
and competing with man for food may have led, by natural selection,
to changes in behavior related to coexistence with humans. Rattus
rattus, for example, display avoidance of unfamiliar objects such as
traps.
Living in trees or roofs, R. rattus tend to flee upward. These do
not burrow or swim but climb and nest above ground.
They construct a loose, spherical nest of shredded vegetation,
cloth, or other suitable material.
The black rat is a territorial, sociable animal, sometimes forming
clans of up to sixty animals. Social groups usually
contain a single dominant male and sometimes a linear male hierarchy.
There are also two or three top females, subordinate to the males
but dominant to the rest of the group. Females display more
aggressive behavior than males. The feeding territory is defended
against outsiders by biting, jumping, and standing on hind legs and
hitting with the front paws. The infants in the group have immunity
from aggression and can take food from the dominant adults.
Food Habits
Rattus rattus are omnivorous. They eat seeds, nuts, vegetables,
fruits, insects, invertebrates, and other materials such as soap,
paper, hides, and beeswax. Food may be carried back to the nest and
stored. In captivity they should be offered a complete diet of
rodent lab blocks, and rat or mouse
mix, with bits of fruit or veggies regularly. Cheerios or wheat
bread are great treats, in small quantities. Do NOT feed chocolate,
fried foods, salted foods, candy or junk food! They may enjoy
crickets and mealworms if they are captive bred, never feed wild
insects as they may carry parasites. Vitamins, like Nutri-Cal are a good addition to their diet, and added calcium
during nursing and growth due to demands on their systems at those
times, but take care not to overdo it. Water bottles should be used
to proved constant, clean water. Ceramic or stoneware food dishes
work well for keeping seeds or fresh foods off the floor, and a wire
mesh hopper that allows them to eat the lab blocks through without
extra waste.
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