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North America Lloyd, 1983; Reynolds, 1985. Following introductions, from 1876 to1929, gray squirrels largely replaced red squirrels throughout much of England and
Wales. Recent research suggests that this replacement occurred not as a result of direct competition, but rather as a result of gray squirrels carrying a novel poxvirus that is lethal
to red squirrels but causes little or no serious illness in gray squirrels Thomas et al., 2003. Populations of gray squirrels also occur in Scotland, Ireland and northern Italy Po
Valley, where they were introduced during the late 1940s. Gray squirrels are most com- mon in deciduous and mixed woodlands, parks and gardens. They are considered a pest
species in some countries, though others welcome them as interesting garden visitors. Common tree squirrels in North America include the gray squirrel and fox squirrel
Sciurus niger in the eastern United States. Both species are common in urban environ- ments, and the latter has been introduced into various cities in the western United States.
Other kinds of tree squirrels, including American red squirrels Tamiasciurus hudsoni- cus
, Douglas squirrels Tamiasciurus douglasii and western gray squirrels Sciurus gri- seus
, are less likely to be found in urban areas, but Tamiasciurus spp. occasionally invade attics and wall spaces in mountainous areas.
Although tree squirrels forage on the ground, they rarely stray far from a tree, where they can flee to safety. Common foods for these squirrels include nuts, berries, buds,
fungi, insects, and sometimes bird eggs or small animals. Their nests are built in trees from twigs, shredded bark, leaves and sometimes moss. When available, hollows in tree
trunks are often used as nesting sites. Densities of red squirrels can range from 0.2 squir- relha to 1.6 squirrelsha in coniferous or broadleaved forests. These squirrels also can
occur at high densities in parks and gardens, raising the likelihood of contact with peo- ple. European red squirrels produce 1–2 litters a year, depending on latitude, with 3–4
young per litter; reproductive rates for the invasive gray squirrels are similar, as are those of fox squirrels.
13.2.2. Flying squirrels
Flying squirrels, such as the southern flying squirrel Glaucomys volans and the northern flying squirrel Glaucomys sabrinus, are common nocturnal inhabitants in many forests
and some semi-rural and suburban landscapes in North America. These animals do not actually fly but are able to glide with the help of a large skin membrane patagium that
runs alongside the body from the forelimbs to the hindlimbs Eisenberg, 1981. As the flying squirrel stretches out its limbs, the membrane becomes taut and forms an air-resis-
tant surface that allows the animal to remain aloft for many seconds. The relatively com- mon southern flying squirrel frequently lives in attics or wall spaces Banfield, 1974, but
it often goes unnoticed because of its secretiveness and nocturnal habits. Its food consists primarily of nuts, seeds, fruits, bark, fungi, lichens and insects. Flying squirrel females can
mate twice a year and typically give birth to 1–6 young after a gestation period of about 40 days. Births usually occur from late winter to early spring and from early summer to
midsummer. Another flying squirrel species, the Siberian flying squirrel Pteromys volans, exists in some regions of Europe, but has little impact on people, because it rarely enters
human environs and is experiencing population declines, as tracts of birch, spruce and pine forest are destroyed to make way for human development Grzimek, 1975.
Non-commensal rodents and lagomorphs
422
13.1. Introduction
Many species of non-commensal or so-called wild rodents, as well as various rabbits and hares, occur as interesting and usually harmless residents of wilderness and rural regions
of Europe and North America. In such settings, these animals usually have negligible impacts on human health and economic well-being, although a few species occasionally
do cause damage to crops, pastures and forest plantations. Unfortunately, when these same animals occur near human habitations, work sites or recreational areas, they can
serve as sources of disease and cause significant damage to homes or other sites. Based on current economic development and housing trends, it appears inevitable that an increa-
sing number of people will come in contact with non-commensal rodents, rabbits and hares found in rural or wilderness landscapes undergoing conversion to more urbanized
environments.
This chapter discusses the major types of rodents, rabbits and hares likely to be encoun- tered in areas undergoing urbanization. It also discusses the health and economic risks
these animals pose, how aspects of their biology affect these risks, and what steps can be taken to reduce human exposure to non-commensal rodents, rabbits and hares, and the
diseases they carry. Additional information on the health-related effects of these animals in Europe and North America can be found in a recently published book by Gratz 2006
13.2. Types, distribution and abundance
The following subsections discuss briefly the distribution and biology of major rodent groups order: Rodentia; families: Muridae, Sciuridae, Myoxidae and Castoridae most
likely to be encountered in areas undergoing urban sprawl in Europe or North America. Emphasis will be placed on the factors that affect the abundance of these animals and the
likelihood they will come in contact with people. Unless stated otherwise, basic infor- mation on the habitats, distributions, abundance, reproduction and foods of these ani-
mals, as well as their interactions with people, was obtained from the following standard mammalian reference works: Cahalane 1961; Grzimek 1968; van den Brink 1968;
Hall 1981; MacDonald 1984; Nowak 1991; MacDonald Barrett 1993; Alderton 1996; Nowak 1999; Nechay 2000; MacDonald 2001. Additional citations specific to
each type of rodent are also provided in some instances. Similar discussions that use infor- mation obtained from the same literature sources listed above for rodents are provided
for ecologically similar rabbits and hares order: Lagomorpha; family: Leporidae – hereafter referred to as lagomorphs.
13.2.1. Tree squirrels
These attractive and highly visible animals primarily Sciurus spp. provide a classic exam- ple of the successful use of urbanized environments by rodents. The European red squir-
rel Sciurus vulgaris is the most common European tree squirrel and is widespread across much of the continent. However, it has been displaced in some areas, such as in the
United Kingdom, by the gray squirrel Sciurus carolinensis, a species introduced from
Public Health Significance of Urban Pests
425
in newly constructed human dwellings being scattered among the large patches of native vegetation preferred by these animals. The species most likely to be found near human
habitations is the white-tailed antelope ground squirrel Ammospermophilus leucurus, which rarely causes significant damage to residential vegetation or property Belk
Smith, 1991. These animals prefer sites with gravelly soils covered by grasses and sage- brush, greasewood, shadscale or creosote bush. Their burrows can be recognized by the
radiating pathways that merge at the burrow entrance, which lacks a mound and can be somewhat inconspicuous Zeveloff, 1988. They feed primarily on seeds and the green
portions of forbs and grasses. Typically, a litter of 5–14 young is born in the spring and, occasionally, a second litter will be produced in a given breeding season.
The so-called prairie dogs are not actually dogs, but rather are large burrowing squirrels of the genus Cynomys. Their unusual name comes from the bark-like calls they make to
warn other colony members of potential dangers. Each of the five North American spe- cies exhibits highly complex social behaviour and lives in large colonies that can include
thousands of individuals living in well-defined family groups, called coteries Clark, Hoffman Nadler, 1971; Pizzimenti Hoffmann, 1973; Pizzimenti Collier, 1975;
Ceballos Wilson, 1985; Hoogland, 1995. Their food consists primarily of grasses and other plants, but insects and even smaller rodents are eaten occasionally. Each year fema-
les give birth to a single litter of about four pups. Mexican and Utah prairie dogs Cynomys mexicanus
and Cynomys parvidens, respectively have the most limited distributions and live in fairly remote areas Long, 2002. Both are considered threatened and are rarely
encountered by people. White-tailed prairie dogs Cynomys leucurus are quite abundant and widespread, but also typically live in environments far removed from major urba-
nized areas Clark, Hoffmann Nadler, 1971. The closely related Gunnison’s prairie dog Cynomys gunnisoni is found on the Colorado Plateau and surrounding regions of the
south-western United States. Unlike the above three species, Gunnison’s prairie dogs often establish colonies near human dwellings. The final species is the black-tailed prai-
rie dog Cynomys ludovicianus of the plains grasslands located east of the Rocky Mountains Hoogland, 1995.
Among the five prairie dog species, the black-tailed prairie dog is most likely to occur in close proximity to people, being fairly common in many suburban and even some urban
areas, particularly those along the Front Range of the Colorado Rocky Mountains, a region that includes the Denver Metropolitan Area and numerous smaller cities. In some
instances, small colonies of this species occur in isolated patches of habitat that are almost completely surrounded by urban development. When living in urbanized environments,
prairie dogs can damage shrubs or other plants that are eaten for food or instinctively cropped, to reduce the risk of being ambushed by predators, such as coyotes Canis latrans
or American badgers Taxidea taxus.
13.2.4. Chipmunks
