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well as on occasional invertebrates. Their name comes from the distinctive nests they build, which consist of large piles of sticks that are often placed at the base of a tree or
other sizeable plant, although the nests of Mexican wood rats Neotoma mexicana are constructed in large cracks in cliff faces, along the walls of caves or under large rocks.
Many species in the western United States and Mexico cover their stick nests with pieces of spine-bearing cactus to provide additional protection against predators. If left undis-
turbed, wood rats will continue to add items to their nests until they become quite large. Bonaccorso Brown 1972 reported that a single desert wood rat Neotoma lepida could
build a complete nest 40 cm high and 100 cm wide over a period of 7–10 days. Wood rats are highly territorial, and the valuable nest sites are defended vigorously, rarely remaining
unoccupied for long periods. In some instances, nests can exist for many decades and per- haps even longer, being enlarged by each new resident. Several species of Neotoma are
known to build their nests in the walls or crawl spaces of homes, garages or other buil- dings. The gnawing activities of these rats, as well as the extensive piles of excreta asso-
ciated with their nests, can result in damage to homes or other property and cause an unsightly mess. Female wood rats in the northern part of the continent typically produce
a litter a year, while those living in more southerly areas sometimes have two litters a year. The average litter size is 2–6 pups. Wood rats do not become sexually mature for 7–8
months after birth, and they live longer-than deer mice; one wood rat in captivity lived for nearly 8 years, although lifespans of 3–5 years are probably more typical in the wild.
Cotton rats, of the genus Sigmodon, are common in grassy and weedy fields in many areas of southern North America. The most important species in the temperate regions of the
continent is the hispid cotton rat Sigmodon hispidus, which is often extremely abundant in thick grassy habitats in the south-eastern and south-central United States Cameron
Spencer, 1981. In many ways, the behaviour and ecology of cotton rats resemble those of voles, which are more common in the northern parts of the continent. These similarities
include not only types of habitats selected, but also include the construction of grass nests and runways, extremely high reproduction rates and populations that often fluctuate dra-
matically from year to year. In the warmer portions of its range, the hispid cotton rat can breed year-round. Females produce several litters a year, with up to 15 young in each lit-
ter. Most cotton rats that survive to breed live less than 2 years. Their activity typically peaks around dawn and dusk, during which time they forage on various types of green
vegetation, as well as on the occasional insect or bird egg. Cotton rats can be quite des- tructive to some crops, including sugar cane and sweet potatoes.
13.2.11. Rabbits and hares
Rabbits and hares are not rodents, but rather belong to the family Leporidae within the mammalian order Lagomorpha, which also includes pikas. The most notable difference
between lagomorphs and rodents is the possession of an extra pair of incisors in the for- mer group. Rabbits and hares are extremely widespread, occupying habitats from the
tropics to the Arctic, including forests, deserts, grasslands, wetlands and mountainous areas. All species are long-eared, grazing animals with elongated limbs for running quic-
kly over open ground. Their large eyes, placed on the side of the head, improve their chances of detecting approaching predators, even in dim light. These animals also have
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430
species also occur on the continent, the ones most likely to be encountered by people are the fat or edible dormouse Myoxus glis, formerly Glis glis, the common or hazel dor-
mouse Muscardinus avellanarius, the garden dormouse Eliomys quercinus, and the forest dormouse Dryomys nitedula. Dormice typically live in wooded areas, hedgerows and
rocky places, but will enter gardens or other areas near human dwellings. They find shel- ter in hollow trees, rock crevices and abandoned burrows, where they build a nest of plant
materials. Given the opportunity, these rodents also will build nests in building attics or barns. Dormice are normally nocturnal, but can be active at dawn or dusk. Their diet
consists primarily of nuts, fruits, insects, eggs and small vertebrates. In the northern por- tions of their range, dormice put on considerable fat in the fall and hibernate during the
winter, waking only occasionally to feed on stored food items. Females give birth to one or two litters a year, with each litter containing 2–10 young. Dormice are believed to live
for 5–6 years in the wild. Although they occasionally can become nuisances and damage wine grapes and fruits, dormouse populations are typically so small that they have little
impact on people.
13.2.10. N ew World rats and mice
The New World murine subfamily Sigmodontinae contains a wide variety of species, including some that occur near human habitations. The most important genera are
Peromyscus deer mice and their allies, Neotoma wood rats and Sigmodon cotton rats.
Carlton 1989 recognized 53 species of Peromyscus, and all of these are likely to invade human dwellings under certain circumstances Cahalane, 1961. However, the two spe-
cies of Peromyscus most likely to be encountered by people are the widespread deer mouse Peromyscus maniculatus and white-footed mouse Peromyscus leucopus King, 1968; Kays
Wilson, 2002. Both species are abundant over large areas of North America, with the deer mouse occupying all but the south-eastern portion of temperate North America and
the white-footed mouse occurring over the eastern half of the continent and in portions of the south-western United States. In many respects, including behaviour, appearance
and general ecology, these mice resemble European species of Apodemus mice and can be considered ecological equivalents. Peromyscus mice consume a variety of seeds, other vege-
table matter and often insects. Deer mice are particularly common in grasslands or mixed grass and brush habitats; white-footed mice are more likely to occur in woodland or
mixed woodland and brush habitats. Both species will enter homes and other buildings, particularly as winter approaches. Although they can be quite abundant, these mice are
nocturnal and, therefore, rarely observed. Their nests usually consist of a mass of grass, leaves and other soft debris, although deer mice, like certain other Peromyscus spp., occa-
sionally construct short, shallow burrows. Females give birth to up to four litters a year, with 1–9 young per litter. Lifespans of Peromyscus mice rarely exceed 2 years. Their gna-
wing near nest entry points on homes or other structures can cause limited damage to wood siding and their excreta can create an unsanitary situation.
Although wood rats Neotoma spp. occur in both the eastern and western portions of temperate North America, the diversity of species is greatest in the western half of the
continent. These rats feed on a variety of seeds, berries and other vegetable matter, as
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lower elevation sites than the latter, which is more likely to be found in less arid and more mountainous habitats Chapman, 1975; Chapman Willner, 1978.
13.3. Biological factors of relevance to human health
