Cornwall Mammal Group
Recognition:
Although the house mouse is mainly associated with house and business premises it also occurs in the countryside
and in gardens. The house mouse is normally found within a few metres of its food
source. This small mouse is grey-brown all
over with greasy fur and a long, bald, scaly tail. Mice living in colder environments (they have been known to set up home in frozen meat stores) may have distinctly longer fur. The large ears are pinkish and the black eyes are relatively small. The body can be up to
100 mm long and the tail almost as long again. Adult house mice weigh between 12
and 22 g. Juvenile wood mice may be a similar colour, but the house mouse has
smaller ears and eyes and a narrower head. Unlike other mice, the house mouse has a strong musky smell. Young rats may look superficially similar to house mice but the eyes and ears of mice are proportionally larger, and the tail more slender, than those of the rat; the feet of young rats also appear larger relative to the body. In owl pellets the skulls of house mice can be distinguished from those of wood mice by the shape of their incisor teeth and the number of molar roots.
House mice excavate tunnels in outdoor environments. Indoors they will frequently
gnaw through obstructions. The small prints are not distinctive but the tail may leave drag marks. The house mouse uses scent to mark its territory and this musky smell may be detected along with urine staining of marking sites. The droppings are about 7 mm long and often deposited at latrine sites. Mouse droppings can be differentiated from those of bats as the mouse droppings are hard, whilst those of bats crumble easily.
© David Chapman
Originally an inhabitant of desert areas of Asia, the house mouse has spread with the
development of agriculture to every corner of the planet. In the UK it is most often
found in buildings: domestic, agricultural or industrial, but where the larger wood
mouse is absent they may also occur in hedgerows and woodland. Behaviour varies
with habitat, the animals in buildings being more sociable than their open-air cousins, they occupy territories which vary in size according to the food resources, and live in mixed sex groups dominated by a single male.
Mainly active at night, they feed on a range of grains, insects, fruits and fungi, as well as stored human foods. Their adaptable appetites are key to their success: wild-living animals feed mainly on insects, supplemented with grain. They are happy to eat many human and animal food stuffs and even such exotic items as soap and tobacco. House mice take in most of their liquids from their diet and rarely drink. Mice are very messy eaters, they typically damage much more grain than they eat and often contaminate it with their droppings and urine. Their habit of gnawing, an activity which they carry out to wear down their constantly growing front teeth, is a major problem and has been known to cause fires when electric wiring is damaged.
House mice breed throughout the year at monthly intervals. Females mate with the
dominant male and give birth to litters of 4 to 8 pups. Females in breeding groups will
often pool their young and even nurse the pups of other females. The young are
weaned at 3 weeks and are sexually mature at 6 weeks. Few animals survive beyond
18 months.
In the fields house mice are vulnerable to all the usual predators of small mammals
but in buildings most die from poisoning, cold or disease. Rats are a major predator
and domestic cats often kill house mice. Improvements in buildings and storage have
resulted in house mice being less common than they were 50 years ago.
Distribution:
The house mouse occurs across Cornwall and the Isles of Scilly with most recent records from the east probably reflecting recorder effort. The house mouse originated around Iran and spread throughout the Mediterranean and Europe alongside the development of agriculture.
Now occurring throughout the UK and Ireland it is also found around the world, from the Arctic to South Georgia.
Records:
2007-2012: 275
2002-2007: 369
Pre-2001: 109
Total: 753
Cornish Tales:
The older buildings of Cornwall are home to many small mammals and the scampering of tiny feet in the attic is more likely to be wood mice, bank voles, or shrews than house mice.
Did you know?:
The mouse’s tail is used to regulate body temperature and mice from colder
regions have shorter tails. The laboratory mouse is a highly inbred albino variety of the house mouse.
Conservation:
This highly successful colonist is not regarded as being of conservation
concern. It is a major pest of domestic, agricultural and industrial premises where it eats a range of materials and contaminates others with urine or droppings.
Survey Methods:
Small mammal trapping. Owl pellet analysis. Records are also collected from pest control reports, cat kills and incidental sightings from bird feeders and mouse traps.
