Vole

Vole is an organism similar to the rodents, they are often confused with the mouse or other rodent species. Vole meaning can be defined as the small-bodied mouse-like rodents of the Northern Hemisphere that belong to the family of Cricetidae. The family Cricetidae is further classified into the subfamily called Arvicolinae. The vole is classified into this subfamily. The subfamily of the vole are shared with many other species, the example of species that share this subfamily is small-bodied mouselike rodents, lemmings, and some other animals. This article focuses on the general description of the voles, taxonomic classification of the voles, the general behaviour and genetics of the organism. 

They are also commonly known as field mice. The other common name that is mostly used in Northern America is meadow mice. There are about 150 to 170 species of the voles. The taxonomic classification of the voles is complicated because of the number of species that are classified under this subfamily. The number of species varies in different taxonomic classifications. 

The article also focuses on the lifespan and reproduction of the organism.

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Taxonomic Classification

The vole belongs to the Animalia kingdom, this kingdom consists of all the multicellular eukaryotic organisms. They are further classified into phylum. They belong to the phylum called Chordata. The characteristic feature that is commonly used to classify the animals belonging to this category is the presence of the vertebral column or the spinal cord. The more specific features that are required to be present to be classified as chordate include the presence of the following five during any stage of their life span, the characteristics are as follows,  notochord, dorsal hollow nerve cord, endostyle or thyroid, pharyngeal slits, and a post-anal tail. The name chordates have originated from the notochord, suggesting the presence of it as an important feature.

The phylum is then classified into classes. The voles belong to the class called Mammalia, the characteristic feature of this class is the ability to produce progeny, that is the animals classified under this class give birth to the progeny rather than laying eggs. Another characteristic feature of the vole is the presence of mammary glands in the female. The class is further divided into orders, the voles are classified into the order named Rodentia.

It is clear from the discussion that voles are similar to rodents, because of these similarities they are classified into the order Rodentia which is shared by rodents and lemmings. The characteristic feature of this classification order is the presence of a single pair of incisors (that is 2 incisors) present on both upper and lower jaws. The other characteristic feature of these incisors is that they are continuously growing and are common to all the members of the Rodentia order. Most rodents are small animals with robust bodies, short limbs, and long tails but the voles are different in their morphology as the physical feature of the animal can be defined as the stouter body; a shorter, hairy tail; a slight rounder head. They are also different in their molar dentition, the voles have a  high-crowned molar with angular cusps, whereas the molar dentition in the rodents and lemmings can be defined as the lower crown and the cusp is rather oval in shape.

The order is further differentiated into family and subfamily. The voles are classified into the family called Cricetidae. The family consists of members like hamsters, lemmings, rodents, and voles. The feature of this family is the presence of the same detention pattern and the dental formula. The voles belong to the subfamily that is classified under this family. The name of the subfamily is Arvicolinae. The subfamily is also shared by the rodents, lemmings and hamsters. The characteristic feature is the presence of the molar teeth, the teeth of these subfamily members are defined as prismatic cusps in the shape of alternating triangles.

Voles contain the following groups, there are about 170 species that are classified into these groups, the number of the species varies in different taxonomic classifications but this is the most widely accepted form of the classification. The groups are as follows:

1. Arborimus – tree voles

2. Arvicolini

3. Ellobiusini – mole voles

4. Myodini

5. Phenacomys – heather voles

6. Pliomyini

7. Prometheomyini

Physical Features of Vole

They are similar to rodents, and the most important physical feature is the presence of incisors on both the upper and lower jaws. There is only a single pair of incisors that is present. The dental formula of the voles can be defined as 1003 / 1003. The dental formula represents the number of teeth present in the voles. There are 1 pair of incisors, 0 canine, 0 premolars, and 3 molar teeth. The molar teeth shape can be defined as prismatic cusps in the shape of alternating triangles. The incisors are the main teeth that are used for survival.

The physical appearance of the voles can be defined as the hairy small animal that has a stouter body shape. The overall body size of the mole can be defined as 3–9 inches which are approximately about 7.6–22.9 cm, the body size of the voles varies according to the species. A general question that is often asked is “ do voles have eyes?” The answer to that question is that voles have eyes. Voles generally have small eyes and ears when compared to their rodent counterparts. The ears of the voles are rather shorter when compared to the vole. Voles have blunt muzzles rather than the tapered form commonly found in other rodents.

The bodyweight of the vole varies according to the species, the vole can have bodyweight ranging from 35 grams to 250 grams. The smallest vole has a bodyweight of fewer than 35 grams. The smallest vole species is termed the Microtus pinetorum, they are commonly known as the woodland vole. The body size of the voles can range from less than 3cm to less than 4 inches. The largest vole belongs to the species called Arvicola terrestris. These species are native to Eurasia, they are commonly known as the water vole because of the choice of their habitat. The body size of the water vole can range up to 22 cm which when converted is about  9 inches long. The tail of the animal ranger up to a length of 13 cm which is approximately 5 inches. The bodyweight of the largest vole, also known as water vole can range up to 250 grams.

The colour of the voles are similar to that of rodents, but voles are majorly found in the following colours, solid grey, brown, chestnut, or reddish on the upper parts. The side of the body can be grey or slightly blackish in colour. Compared to the upper part of the body, the inner region or the lower part is generally white or pale in colour. Sometimes the underparts are greyish in colour.

Another common species of voles that are used to define the morphology of the animal is meadow voles, these voles belong to the species called, M. pennsylvanicus. These are the most common mammals found in Northern America. The body weight of the mammal can range up to 50 grams which are about 2 ounces, the adult member of the species can grow roughly up to 15 to 20 cm which is about 6 to 8 inches in length, animal this species has a short tail the length of the tail is about 3 to 6 cm, this measurement is included in the complete body length. The body of these voles is covered in dense fur, the colour of the fur is generally chestnut brown, the underparts of the body are generally greyish but are sometimes dark in colour.

Diet 

Voles are termed as burrowing animals, this is so because of their ability to dig holes in soil especially that resembles tunnels. The holes are dug to reach the plant roots and bulbs that are the main diet of the animals. Voles diet includes mostly small plants and roots but they can also eat dead mice and rats. Another important constituent of the diet is nuts, voles are able to digest almost all varieties of nuts and can live on a nut-based diet without developing any serious health conditions. Voles prefer eating succulent root systems that are found under the soil, the second preference of the voles are bulbs. Voles are also considered agricultural pests because they eat and girdle till the plant is completely dead. The burrowing ability of the voles also helps them in detecting and eating the underground bulbs. Although the diet includes primarily the above-mentioned food sources, voles are also seen eating some fungi and members of the insect family. Thus the diet of a vole can be considered as an omnivorous diet.

Habitat and Distribution of Voles

Voles are the most common mammal found in the Northern Hemisphere, they are the largest group of mammals that are found in the United States of America. Vole meaning can be defined as the terrestrial animal which belongs to the order Rodentia and shares similarity with the members of the order like rodents, lemmings, and hamsters. Since voles are classified as an abundant genus of mammals their habitat is very diverse, they can survive in varying temperature and environmental stress conditions. Voles are found in habitats near sea level to the habitat near the mountains, the forest that is seen as the habitat of vole include the following, prairies, steppes, semi-deserts, alpine and subalpine meadows, treeless tundra, and several types of forest, including cloud, deciduous, and coniferous.

Voles are widely distributed in the Northern hemisphere they are very commonly found in the following areas In North America they range from Alaska southward to the mountains of Mexico and Guatemala. In regions like Eurasia, they are distributed across the British Isles and across Europe and Asia. The countries of the Asian continent that contain the population of voles include the following, China, Taiwan, and Japan. Voles are not an isolated population except for African voles that exist as an isolated population in coastal Libya.

Voles are considered terrestrial mammals but there are few exceptions to this generalization. The Arboreal red and Sonoma tree voles belong to the species called Arborimus longicaudus and A. pomo, respectively are inhabitants of the humid coastal old-growth forests of northern California and Oregon. Voles are known for their burrowing capabilities and they live on land, usually by digging holes on land but these exceptions are generally seen living on the nest. They build nests on the tops of Douglas fir, grand fir, and Sitka spruce trees. The diet of these voles is also adapted according to the habitat, the diet of these voles mainly includes outer parts of conifer needles particularly Douglas fir. 

Another exception to the terrestrial habitat is the sei aquatic species known as M. richardsoni. They are commonly known as American water voles, they are inhabitants of areas near clear springs. They are very good swimmers, they live in burrows but their burrows can be at water levels or submerged. The diet of American water voles consists of roots, rhizomes, and preformed buds of perennials. 

Predators 

Since voles are considered agricultural pests they are mostly terminated by farmers to prevent their crops, apart from humans the list of the natural predators of voles is also very long. Some of the natural predators of the voles are listed below:

1.  Martens

2.  Owls

3.  Hawks

4. Falcons

5.  Coyotes

6. Bobcats

7.  Foxes

8. Raccoons

9. Snake

10. Weasels

11. Domestic cats and lynxes

Some of the less common predators of the voles include owls, there are some species of owls that predate on voles. Examples of such species are as follows, the short-eared owl, the northern spotted owl, the saw-whet owl, the barn owl, the great grey owl, and the northern pygmy owl.

Lifespan of Voles

The life span of voles ranges from species to species but the average lifespan of the vole can be termed as three to six months for smaller moles. The larger moles can live up to 12 months. The mortality rate of the voles is very high; it is estimated that about 88% of voles die during their first month.

Mating System

The voles are both polygamous and monogamous based on their species. The mating system and pattern vary from species to species. Examples of monogamous species of voles include the following, the prairie vole, the woodland vole. The example of polygamous vole includes the following species,  meadow vole, water voles. The choice of homogamous or polygamous mating system depends on the presence of resources. It is seen that when the resources are homogeneously distributed the species opt for the monogamous mating system. Similarly in the case of scarce or heterogeneous or clustered resource distribution the species opt for a polygamous mating system.

It is also important to note that the polygamous mating system is generally of the polyandry type, where a single male mates with different females. The mating is based on asserting dominance. The dominance of a male is established by the territory. The female choice is based on the territory. In a polygamous mating system, parental care is negligible, especially since the male members of the species do not participate in raising the young one. One of the main reasons for a polygamous society is the drastic difference in the sex ratio of males and females.

In monogamous species, a pair mates for the complete life span. Parental care is provided by both the male and female members of the species. The operational sex ratio in the monogamous population is approximately equal. Monogamy is preferred when resources are spatially homogeneous and population densities are low. 

There are no evident examples that show inbreeding depression or inbreeding among the species of voles. One important thing about voles is their high fecundity. Voles have a number of unusual chromosomal traits that are not seen in mammalian species, some of them are as follows.

1.  Some of the species have been found with 17 to 64 chromosomes.

2.  In some species, males and females have different numbers of chromosomes. 

3. The genetic material that is only found on the Y chromosome (found in males) is found in both males and females.

4. In some of the species, the Y chromosome is entirely lost, the example of such includes Microtus oregoni, commonly known as creeping vole.

The common question that comes to mind when discussing vole is “what is a vole?” Vole meaning is referred to as a terrestrial mammalian animal that belongs to the order Rodentia and shares similarities with rodents and hamsters. The animals are characterized by their detention and smaller but straight bodies. Another common question is “do voles have eyes?” This generally arises due to the exceptionally smaller size of eyes and ears when compared to their fellow order member rodents and lemmings. Voles do have eyes but they are very small in shape. Voles are found on a variety of landscapes but they are majorly terrestrial mammals, some of the exceptions are the American water voles that are defined as semi-aquatic species. The diet of the voles is mainly based on plant roots, bulbs, and nuts, but they can also eat small insects, fungi, and dead mice. There are various natural predators of animals including cats, foxes, and some owls. The life span of the animal varies with species. For smaller species, it is 3 to 4 months while for larger it is about 12 months.