Public Health Significance of Urban Pests
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range water voles seem to prefer pastures over more typical riparian habitats. Due to pre- dation by introduced American mink Mustela vison, loss of suitable riverside habitat
and water pollution, water vole populations in the United Kingdom have declined by as much as 90 over the past 25 years. These animals eat various grasses, sedges and other
plants found growing near the edge of their aquatic homes. Water voles also consume cereal grains and fruits, including apples. Breeding takes place from April to October,
with females producing 3–4 litters of 2–7 young per litter. Few water voles live more than a year. If these animals are numerous, their burrowing activities can damage dikes
and canals.
Muskrats Ondatra zibethicus are basically large aquatic voles that are native to North America, but they have been transplanted to many regions in Europe. They are quite
abundant throughout much of North America and occur frequently in ponds and water- ways in suburban and largely urban areas. Muskrats require aquatic habitats with suita-
ble aquatic vegetation for food and shelter. They are valued for their fur, and their tun- nelling activities can cause damage to dikes and stream banks Danell, 1977; Corbet, 1978.
13.2.8. Old World mice
Mice of the genus Apodemusare quite widespread and abundant. They eat primarily gras- ses, seeds, nuts, fruits and other plant materials, as well as some insects and snails. Their
nests are made from finely shredded grasses. Apodemus mice can produce up to five lit- ters a year with each litter containing about six young. Striped field mice Apodemus agra-
rius
and wood mice Apodemus sylvaticus are the most ubiquitous and persistent small mammal species in many urban areas of Europe Montgomery, 1976; Babinska-Werka,
Gliwicz Goszczynski, 1981. The striped field mouse is widespread in eastern Europe, with western populations reaching Germany and Northern Italy. These mice can be very
abundant in fields, scrub and woodlands associated with damp habitats and river valleys. They also may enter houses, barns and stables and have been reported to colonize such
highly urbanized areas as Warsaw, Poland Andrzejewski et al., 1978. The related wood mouse is widespread in woodlands, scrubland and dune areas throughout continental
Europe, the British Isles and southern Scandinavia, having a range that extends as far as the southern part of western Siberia, northern Kazakhstan and the mountains of central
Asia. Being highly adaptable, they often occupy gardens and city parks and will enter houses in winter, particularly when house mice are absent. Another species of Apodemus,
the yellow-necked mouse Apodemus flavicollis is common in woodlands, hedgerows, field margins, orchards and wooded gardens. Yellow-necked mice are more common
than wood mice in alpine coniferous forests, but are less common than the latter in open scrub and fields. Yellow-necked mice also frequently enter homes as winter approaches,
but typically depart by spring. They are known to store caches of nuts in small spaces and under floorboards.
13.2.9. Dormice
These squirrel-like rodents occur over much of Europe, although deforestation has seve- rely impacted some species Pucek, 1989; Amori, Cantini Rota, 1995. Although other
Non-commensal rodents and lagomorphs
428
More than 40 species of Microtus voles are known to exist. Important European species include the common vole Microtus arvalis, root vole Microtus oeconomus and the field
or short-tailed vole Microtus agrestis. The common vole is predominant in the eastern half of the continent, but the most frequently encountered vole in many western
European countries, except Ireland, is the field vole, a species that has declined in some areas but remains abundant in open grasslands and damp pastures. These three European
species of Microtus voles also occur often in gardens and open woodlands, as they seek out their primary food sources, which consist of grasses, as well as the stems, roots and
bark of other plants. The foraging activities of field voles also can occasionally result in damage to newly sown cornfields. As these animals travel through the grass and low-
lying vegetation of their home ranges, which are about 100–150m in diameter, they form a characteristic network of runways that are shared by other voles and provide some pro-
tection from predators.
Field vole populations also fluctuate greatly from year to year, though not as dramati- cally as those of the related lemmings. Even among rodents, Microtus voles are notable for
their ability to quickly increase their reproductive rates in response to the availability of new resources or improved habitats Elton, 1942; Begon, Harper Townsend, 1996. In
some instances, their numbers increase so greatly that they cause extensive damage to pastures, cornfields or forest plantations. Densities of voles during such so-called vole
plagues have reached as high as 4,900 volesha. The field vole breeding season is from February to September, after which females produce as many as 10 litters a year, with
3–7 offspring per litter. Females can become sexually mature as soon as 3 weeks after their birth. These animals eat primarily grasses, stems, new plant shoots, roots, bulbs and
bark, as well as some insects.
At least 17 species of Microtus voles occur in North America. Among the most impor- tant of these are the meadow vole Microtus pennsylvanicus, California vole Microtus cali-
fornicus , prairie vole Microtus ochrogaster, montane vole Microtus montanus and long-
tailed vole Microtus longicaudus. The meadow vole occurs in moist grassy fields and meadows over much of the northern two thirds of North America. Some have claimed
that it is the most prolific mammal on earth Kays Wilson, 2002 and, like most voles, its populations can experience dramatic fluctuations in density Krebs Myers, 1974;
Reich, 1981. At high densities, meadow voles can cause serious damage to woody vege- tation, especially in fruit orchards Byers, 1979. The California vole occurs throughout
much of California and southern Oregon in low-elevation grasslands, wet meadows, coastal wetlands and open oak savannahs with adequate ground cover Kays Wilson,
2002. Prairie voles occur in grasslands in the centre of the continent, and montane and long-tailed voles are found in the mountains of western North America.
The water vole Arvicola terrestris is widespread throughout much of Europe, but is absent from Ireland and most of the Iberian Peninsula. In some areas, such as the United
Kingdom, it usually is closely associated with fresh water such as flooded ditches, slow rivers and lakes and favours steep riverbanks with abundant grass and layered vegeta-
tion. Non-aquatic, fossorial digging or burrowing populations of water voles occur in some regions Meylan, 1975, including central Europe, but in the southern parts of their
Public Health Significance of Urban Pests
431
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
