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Bushy-tailed woodrat
This species was thought to be restricted to higher elevations until very
recently, when the first reports documenting Neotoma cinerea at
elevations as low as 1200 m appeared. These findings lend support to
molecular evidence which had earlier indicated that bushy-tailed
woodrat populations were not isolated on mountain ranges throughout
the Holocene. It is currently unclear whether these lowland
populations are isolated by even lower valleys, or whether this
species can exist in low, xeric areas as well. Bushy-tailed woodrats
are currently found at elevations up to at least 3700 m. During the
Pleistocene, N. cinerea is well-known at lower elevations, and its
range extended south to southern Mexico. Up to thirteen subspecies
are recognized. These subspecies are primarily defined based on
geography and local ecology, and are not universally accepted.
Physical Description
Bushy-tailed woodrats are sexually dimorphic: adult males usually
weigh 300-600 g with an average of 405 g, whereas adult females
usually weigh only 250-350 g with an average of 270 g. These ranges
are relatively large because this species occupies a large
geographic range, and its body size is closely correlated with
climate. Neotoma cinerea is the
largest and most cold-tolerant species of woodrat, and the largest
and most sexually dimorphic individuals of this species are found in
the northern parts of its range. In addition, body size of
bushy-tailed woodrats (examined via fecal pellet size in middens)
has been shown to correlate with known climatic fluctuations over
the past 25,000 years. Woodrats are good climbers and have sharp
claws. They have hypsodont molars with enamel ridges. The color of
the pelage varies across the range, but is usually buff with white
areas around the feet. The bushy tail characteristic of the species
is used to warm the animal.
Reproduction
Some aspects of the reproductive cycle of bushy-tailed woodrats are
still under debate. These animals have been considered polygamous,
polygynous, and/or promiscuous by various authors. Often these
conclusions have been based not on actual observed mating, but on
the size and relative overlap of male and female ranges. Breeding
chiefly occurs in spring and summer (May through August). Females
have small litters (up to six young at a time, though litter sizes
over four tend to suffer losses since the female has only four
mammary glands) but may have up to three litters per year. Modal
litter size is three. Females have been observed breeding as soon as
twelve hours after giving birth, and be may pregnant with one litter
while nursing another. Males fight for access to mates, both through
scent marking and actual physical contact. Fights consist largely of
biting and scratching and may result in serious injury. Gestation
period in captivity is 27-32 days. Newborns weigh approximately 15
g. Eyes open at around 15 days old, and weaning occurs at 26-30
days.
Males are heavier than females from early in development on. By
weaning, males weigh 120-150 g, and females weigh 85-135 g. Females
do not alter their foraging movements between pregnancy, lactation,
and the post-reproductive period -- even though nutrient demands are
higher at certain stages. Heavier females tend to have significantly
more males in their litters than lighter females. Males are larger
and require more energy to raise, though after weaning female
offspring tend to reap more rewards from their mothers via
philopatry. Females breed for the
first time when they are yearlings.
Behavior
One of the most characteristic aspects of woodrat behavior is midden-building.
Middens are often built in caves or crevices, and consist of plant
material, feces, and other materials which are solidified with
crystallized urine. Woodrat urine contains large amounts of
dissolved calcium carbonate and calcium oxalates because of the high
oxalate content of many of the succulent plants which make up the
animals' diets. The mineralogical portion of the urine tends to
crystallize over time, either within the midden or at specific
"urinating posts" frequented by a number of animals over many years.
An important distinction to make is between middens and nests. Nests
are often within the midden, and are the area where the animal is
often found and where females raise young. Bushy-tailed woodrats
also build several food caches, which they utilize during the
winter. These animals do not hibernate.
Bushy-tailed woodrats have fairly small home ranges. It was
previously thought that they never ventured further than 60 m from
their nests, but recent observations have shown that female N.
cinerea may forage as far as 500 m from the nest. These animals are
usually unsocial and solitary, nocturnal, and are strongly
territorial. An exception is the relationship which sometimes
develops between mothers and daughters. It is unclear whether
mother-daughter pairs share nests, but they do have ranges with a
high degree of overlap, and they do share resources. This seems to
be beneficial to the daughter's survival (she benefits from the
mother's food stores) and to the mother's reproductive success
(perhaps because males are more likely to be attracted to a small
area containing more than one female). Besides this mother-daughter
bond, interactions between members of this species are
overwhelmingly agonistic.
Food Habits
Because this species occupies such a wide range of habitats, its
diet is variable. However, N. cinerea may best be described as a
generalist herbivore. Bushy-tailed woodrats
eat lots of woody vegetation, and in drier habitats also concentrate
on succulents. This species gets all of its water from its food and
does not need to drink. Woodrats tend to eat plant materials which
have high concentrations of defensive chemicals; they combat these
defenses by eating only small amounts of each species. Neotoma
cinerea also tends to eat low-energy food items and plants which are
high in oxalates. 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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