Pack rat
A pack rat or packrat, also called a woodrat or trade rat, can be any of the species in the rodent genus Neotoma. Pack rats have a rat-like appearance, with long tails, large ears, and large, black eyes. Pack rats are noticeably larger than deer mice, harvest mice, and grasshopper mice, and are usually somewhat larger than cotton rats.[1]
Woodrats reach their greatest diversity in the deserts of the western United States and northern Mexico. Several species are also found in the deciduous forest of the east coast, juniper woodlands in the southwest, oak woodlands along the coastal western United States and in the Sonoran Desert, and in the forest and rocky habitats of the western United States and western Canada.[5]
Each species of pack rat is generally restricted to a given type of habitat within its range. Pack rats live anywhere from low, hot, dry deserts to cold, rocky slopes above timberline. Pack rats build complex houses or dens made of twigs, cactus joints, and other materials. These contain several nest chambers, food caches, and debris piles. Dens are often built in small caves or rocky crevices, but when close by human habitations, woodrats will opportunistically move into the attics and walls of houses. Some Neotoma species, such as the white-throated woodrat (N. albigula), use the bases of prickly pear or cholla cactus as the sites for their homes, using the cactus’ spines for protection from predators. Others, like the desert woodrat (N. lepida) will build dens around the base of a yucca or cactus, such as jumping and teddy-bear chollas. The largest species, Neotoma cinerea, has a bushy, almost squirrel-like tail. Bushy-tailed woodrats Neotoma cinerea occupy a range of habitats from boreal woodlands to deserts. They are cliff-dwellers and are often found on isolated, high-elevation exposed boulder areas under a variety of temperature and moisture conditions.[6] They require adequate shelter among the rocks, though they are occasionally found inhabiting abandoned buildings as well.
Pack rats are nest builders. They use plant material such as twigs, sticks, and other available debris. They are particularly fond of shiny objects. A peculiar characteristic is that if they find something they want, they will drop what they are currently carrying—for example, a piece of cactus—and “trade” it for the new item. They can also be quite vocal and boisterous. Getting into everything from attics to car engines, stealing their treasures from humans, damaging electrical wiring, and creating general noisy havoc can easily cause them to become a nuisance.[7]
Adult bushy-tailed woodrat males usually weigh 300–600g (10–21 ounces), with an average of 405g (14 ounces), and adult females usually weigh 250–350g (8–12 ounces), with an average of 270g (9.5 ounces.) These ranges are relatively large because this species occupies a large geographic range, and its body size is closely correlated with climate.[9] Average males range in size from 310–470mm (12–18.5 inches), with the average being 379mm (15 inches), and average females range from 272–410mm (10.5–16 inches), with the average being 356mm (14 inches.)
Reproductive habits of rodents are variable in the wild. Offspring are born naked and helpless and must be cared for in nests called middens. Some female pack rats have been known to deliver up to five litters per year with each litter having as many as five young. The offspring may open their eyes between 10 and 12 days after being born and are usually weaned between 14 and 42 days. After around 60 days, most become sexually mature.[7] Populations may cycle approximately every 8 years due to variation in reproduction and juvenile survival.[10] Female annual survival rates vary by age from 0.42 for juveniles to 0.71 for 1–2 year olds,[10] and very few females (less than 5%) live beyond 3 years of age.[10]
