Pack rat

This article is about the rodent. For other uses, see Pack rat (disambiguation).

Packrats Temporal range: Late Cenozoic - Recent
Neotoma cinerea
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Family:	Cricetidae
Subfamily:	Neotominae
Tribe:	Neotomini
Genus:	Neotoma Say & Ord, 1825
Species
Neotoma albigula Neotoma angustapalata Neotoma anthonyi † Neotoma bryanti Neotoma bunkeri † Neotoma chrysomelas Neotoma cinerea Neotoma devia Neotoma floridana Neotoma fuscipes Neotoma goldmani Neotoma lepida Neotoma leucodon Neotoma macrotis Neotoma magister Neotoma martinensis † Neotoma mexicana Neotoma micropus Neotoma nelsoni Neotoma palatina Neotoma phenax Neotoma stephensi

A packrat, also called a woodrat, can be any of the species in the rodent genus Neotoma. Packrats have a rat-like appearance, with long tails, large ears and large black eyes. Compared to deer mice, harvest mice and grasshopper mice, packrats are noticeably larger and are usually somewhat larger than cotton rats.^[1]

A common accepted spelling of "packrat" includes "pack rat". However, according to the American Society of Mammalogists, "packrat" is the official correct spelling.

Species

• Neotoma
• Subgenus (Neotoma)
  • Neotoma albigula - White-throated Woodrat
    • Neotoma albigula varia - Turner Island Woodrat
  • Neotoma angustapalata - Tamaulipan Woodrat
  • Neotoma anthonyi - Anthony's Woodrat †
  • Neotoma bryanti - Bryant's Woodrat
  • Neotoma bunkeri - Bunker's Woodrat †
  • Neotoma chrysomelas - Nicaraguan Woodrat
  • Neotoma devia - Arizona Woodrat
  • Neotoma floridana - Florida Woodrat (Eastern Woodrat)
    • Neotoma floridana smalli - Key Largo Woodrat
  • Neotoma goldmani - Goldman's Woodrat
  • Neotoma lepida - Desert Woodrat
  • Neotoma leucodon - White-toothed Woodrat
  • Neotoma macrotis - Big-eared Woodrat
  • Neotoma magister - Allegheny Woodrat
  • Neotoma martinensis - San Martin Island Woodrat †
  • Neotoma mexicana - Mexican Woodrat
  • Neotoma micropus - Southern Plains Woodrat
  • Neotoma nelsoni - Nelson's Woodrat
  • Neotoma palatina - Bolaos Woodrat
  • Neotoma stephensi - Stephens's Woodrat
• Subgenus (Teanopus)
  • Neotoma phenax - Sonoran Woodrat
• Subgenus (Teonoma)
  • Neotoma cinerea - Bushy-tailed Woodrat
  • Neotoma fuscipes - dusky footed rat

Range and Distribution

Bushy-tailed woodrat range and distribution.

Woodrats reach their greatest diversity in the deserts of the western United States and northern Mexico. However, 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 forest and rocky habitats of the western United States and Western Canada.^[2]

Habitat

Each species of pack rat is generally restricted to a given type of habitat within its range. Packrats live anywhere from low, hot, dry deserts to cold, rocky slopes above timberline. Packrats build complex houses or dens made of twigs, cactus joints and other materials. These contain several nest chambers, food caches as well as 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 base of a prickly pear or cholla cactus as the site for their home, utilizing 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 bouldery exposures under a variety of temperature and moisture regimes. They require adequate shelter inside the rocks, though they are occasionally found inhabiting abandoned buildings as well.

Characteristics

Behavior

Packrats are nest builders. They use plant material like branches, twigs, sticks, and other available debris. Getting into everything from attics to car engines, stealing their ‘treasures’, damaging electrical wiring and creating general noisy havoc can easily cause them to become a nuisance.^[3] 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 are particularly fond of shiny objects. They can also be quite vocal and boisterous, sounding at times as if a "family rift" is taking place.

Diet

The diet of packrats is pretty specific for certain species. For example, the bushy-tailed woodrats feed primarily on green vegetation, twigs, and shoots. A Mexican packrat will feed on seeds, fruits, acorns, and cactus. Then of course packrats are influenced by the things that humans may have in their cabinets or barns.^[4]

Size

Packrats vary in size from species to species. Adult bushy-tailed woodrat males usually weigh 300-600 grams with an average of 405 grams, whereas adult females usually weigh only 250-350 grams with an average of 270 grams. These ranges are relatively large because this species occupies a large geographic range, and its body size is closely correlated with climate.^[5] Average males range in size from 310-470 millimeters with the average being 379 millimeters and average females range from 272 millimeters to 410 millimeters with the average being 356 millimeters.

Reproduction and Life Cycle

Reproductive habits of rodents are extremely variable in the wild and can become more so when domesticated. Most are born naked and helpless and must be cared for in nests. There are some female packrats who have been known to deliver up to 5 litters per year with each litter having as many as 5 young. The offspring may open their eyes between 10 to 12 days after being born and are usually weaned between 14 and 42 days. After around 60 days most become sexually mature.^[6]

Packrat Midden

A large pack rat midden (center) from the Pleistocene period.

A packrat midden is a debris pile constructed by a woodrat. A packrat midden may preserve the materials incorporated into it for up to 50,000 years. The middens may thus be analyzed to reconstruct their original environment, and comparisons between middens allow a record of vegetative and climate change to be built. Examinations and comparisons of pack rat middens have largely supplanted pollen records as a method of study in the regions where they are available.^[7]

Structure

Packrats are known for their characteristic searching of materials to bring back to their dens. These dens can have several debris piles or "middens" where rejected material is put. In natural environments, the dens are normally built out of sticks, cactus joints, rocks or other materials, which are built up in a large pile and provide protection from predators and against thermal fluctuations.

Active pack rat midden in northern Nevada

In the absence of rock crevices or caves, the dens are often built under trees or bushes. The pack rats will also use plant fragments, animal dung and small rocks in building the den. The vast majority of the materials will be from a radius of several dozen yards of the nest. Woodrats often urinate on the debris piles; sugar and other substances in the urine crystallize as it dries out, creating a material known as amberat, which under some conditions can cement the midden together. The resilience of the middens is due to three factors. The crystallized urine dramatically slows the decay of the materials in the midden. The dry climate of the American Southwest further slows the decay, and middens that are protected from the elements under rock overhangs or in caves survive even longer.

Middens as Climate Change Indicators

Zoologists examine the remains of animals in middens to get a sense of the fauna in the neighborhood of the midden, while paleobotanists can reconstruct the vegetation that grew nearby. Because middens are abandoned after a short period of time, they are uncontaminated "time capsules" of several decades of natural life, centuries and millennia after they occurred. The analysis of middens was key in understanding the fauna around Pueblo Bonito, and thus helping to explain its history.

Bushy-tailed woodrat on midden.

According to Bergmann’s rule, the body size of vertebrates is closely related to the average ambient air temperature in the region in which the vertebrae lives. Organisms in warmer regions are typically smaller than members of the same species in colder regions. This is because large body size allows for the conservation of heat, while small body size allows for the dissipation of heat. Due to this, it is believed that the body size of organisms, woodrats in particular, are good indicators of past climate shifts.

Woodrat middens are composed of many things, including plants macrofossils and fecal pellets. The size of the pellet is, as would easily be imagined, proportional to the size of the woodrat. By measuring the pellets, the approximate size of the woodrat is determined based on data from a study of field-trapped woodrats. From Bergmann’s rule, differences in climate then can be determined. A study by Smith, Betancourt, and Brown, published in 1995, involved extensive research on this topic.

Fecal pellets were collected from middens at various sites in the southwest United States know to be, or have been, inhabited only by Neotoma cinerea. From the measurements of the pellets, the woodrat body size was determined. The pellets, as well as the plant macrofossils, were 14C dated to determine the approximate age of the middens. The size of the woodrats relative to modern woodrats was then plotted against the age of middens. The mean annual temperature (MAT) for each site was determined by the deuterium isotope ratio of the plant macrofossils. This data was then plotted against the age of the middens.

By comparing the two graphs, it is clear that the size vs. time and the MAT vs. time are related. In fact, there are practically mirror images of each other. This confirms Bergmann’s rule that as average temperature increases, organism body size gradually decreases. It also shows that the study of body size is a useful method of reconstructing past climate changes. However, more importantly, it shows that at least some species will be able to adapt to the temperature increases caused by anthropogenic global warming.

References

1. ^ San Diego Natural History Museum - Field Guide
2. ^ Packrat Distribution
3. ^ http://www.desertusa.com/mag99/apr/papr/packrats.html
4. ^ http://icwdm.org/handbook/rodents/ro_b133.pdf
5. ^ http://animaldiversity.ummz.umich.edu/site/accounts/information/Neotoma_cinerea.html
6. ^ http://www.desertusa.com/mag99/apr/papr/packrats.html
7. ^ Packrat Midden Research in the Grand Canyon

Works cited

• Betancourt, Julio L., Thomas R. Van Devender, and Paul S. Martin, eds. Packrat Middens: The Last 40,000 Years of Biotic Change, University of Arizona Press, 1990, ISBN 0-8165-1115-2.
• Duff, A. and A. Lawson. 2004. Mammals of the World A Checklist. New Haven, Yale University Press.
• Kays, R. W., and D. E. Wilson. 2002. Mammals of North America. Princeton University Press, Princeton, 240 pp.
• Musser, G. G. and M. D. Carleton. 2005. Superfamily Muroidea. pp. 894–1531 in Mammal Species of the World a Taxonomic and Geographic Reference D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore.
• Ord, G., 1815. "Zoology of North America", in Guthrie's Geography , 2 nd American edition, pp. 291–361. [reprint Rhoads, S.N. Philadelphia, 1894], p. 292.
• Smith, F.A., Betancourt, J.L., and Brown, J.H. 1995. Evolution of body size in the woodrat over the past 25,000 years of climate change. Science, 270: 2012-2014.
• Ulev, Elena 2007. Neotoma cinerea. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [2011, February 25].
• Zakrzewski, J. Richard. Fossil Ondatrini from Western North America. Journal of Mammalogy. Vol. 55, No. 2 (May, 1974), pp. 284–292

External links

• "Desert Woodrats" at DesertUSA.com
• "Packrat Piles: Rodent rubbish provides ice age thermometer", Science News, 24 September 2005