Squirrels, belonging to the rodent family Squirrel family, refers to a large class of rodents with fluffy long hairs on their tails, with about 58 genera and 285 species in existence, distributed throughout all continents outside Antarctica (introduced species in Oceania).
Contrary to most people's impressions, squirrels that live on trees, have large furry tails, and can nibble on pine cones are actually just a small branch of the squirrel species. From snow-capped mountains at an altitude of more than 6,000 meters to tropical islands in the Pacific Ocean, from the Western Hemisphere to the Eastern Hemisphere, in addition to areas with extremely harsh climates and extremely simple vegetation near the polar or driest deserts, species of the Squirrel family are active in various terrestrial habitats, and some also play an extremely important role in ecosystems.
squirrel
origin
Fossils of the earliest known squirrel species come from Eocene strata. It was a long time between 65 million and 35 million years ago. At that time, dinosaurs had just become extinct, mammals had not yet gained control on land, the Tibetan Plateau had not yet become land, Europe and North America were still connected by land, and South America was a huge island. The most primitive squirrels lived in North America and were morphologically close to today's squirrels. Fossils of a series of squirrel species have also been found in the late Eocene strata of North America, unlike any other type of squirrel. The unusually rich fossil squirrel species in North America show that the squirrel family originated in Ephemeric North America and radiated to continents beyond Oceania in the long years that followed, evolving species of different morphologies and adaptations to various environments in the process. Among the existing rodent squirrel suborder species, the sleeping mouse family, which is mainly distributed in Eurasia, and the mountain beaver family distributed in North America, are closely related to the squirrel family. The Squirrel family is the most well-known member of the squirrel family, and it is also the most widely distributed and diverse taxon.
Morphological characteristics
The Eurasian red squirrel (also known as the northern squirrel), which is widely distributed in the temperate coniferous forest belt in northern Eurasia, is a typical representative of the squirrel and the prototype of the well-known squirrel image. The Eurasian red squirrels distributed in the eastern tip of Eurasia have black winter coats and white belly, and the summer coat is brownish red between gray, while the back hair of Eurasian red squirrels distributed in the western tip of Eurasia is brownish red throughout the year. Grayish brownish red is also the main hue of most squirrels in North American forests. The change in coat color of different geographical groups from east to west in the distribution range of Eurasian red squirrels is also a reflection of the historical process of squirrel origin from the North American continent and radiation into Eurasia.
In China, the Taiga forest in the northeast region and Xinjiang is the natural distribution range of the Eurasian red squirrel. The more widely distributed squirrels in broad-leaved forests and mixed coniferous and broad-leaved forests in North China and other places are rock squirrels. Rock squirrels are smaller than Eurasian red squirrels, do not have long hair clusters on their ears, have a grayish yellow color, and are more likely to move down to the ground, especially in rocky areas, hence the name. The chipmunk is also a common squirrel in temperate regions of China. This small animal with black and white longitudinal stripes on its back spends more time foraging on the ground, and often preys on small animals and also eats bark. Red-bellied squirrels are very bold and adapt to disturbed forest habitats, so they can also live well in urban parklands. Red-bellied squirrels live in and around urban parks in and around major cities such as Shanghai, Guangzhou, Chengdu and Kunming, and are the most common wild mammals for urban dwellers in southern China.
Distribution range
It is widely distributed in temperate and temperate forest ecosystems in the Palearctic Boundary, from Iberia and the islands of Great Britain in the west, to kamchatka, Sakhalin in Russia and Hokkaido in Japan in the east, and to the Mediterranean Sea, the Black Sea, northern Mongolia, and northwest and northeast China in the south.
Living environment
Squirrels are mainly distributed in coniferous forests or mixed coniferous and broad-leaved forests composed of pinus, larch (Larix) and spruce (Picea) species. Due to the relatively abundant and stable food source, squirrels can maintain a high population density in mixed coniferous and broad-leaved forests, and can use small woodlands on the outskirts of cities or even cities to become companion animals.
Ecological behavior
1. Rhythm of behavior
Squirrels are active all year round, do not hibernate, are day-to-day animals, and the daily start time of activity is related to sunrise time, while the end activity time is not significantly related to sunset time. The daily activity rhythm of squirrels is affected by climatic conditions, and high winds, heavy rainstorms and severe cold and heat will reduce the activity time of squirrels. The tradeoff between the need for foraging and staying in the nest to conserve energy affects the winter activity pattern of squirrels. In winter, the daily activity rhythm is monomodal, and it will remain in the nest for several days in severe cold weather conditions. In summer, there is a peak in activity in the morning and afternoon. The pattern of daily activity in spring and autumn is between winter and summer.
2. Feeding behavior
Squirrels spend 70% to 80% of their time foraging activities, tending to forage and store in coniferous forests. Autumn squirrels scatter nuts on the ground and fungi on branches. Autumn storage is conducive to squirrel overwintering and second-year fertility. The selection of micro-habitats and the mechanism of re-extraction of squirrel storage have been deeply studied, and have become the hot spots of domestic squirrel ecology research.
3. Community behavior
Squirrels live alone most of the time. Community structures are based on sequences of dominance between the same sexes and between the sexes, and the dominant individuals are usually larger than other individuals. Hierarchical advantages are usually only manifested during the reproductive season. Squirrels use urine and secretions from the mandibular glands to smear on trunks and branches to mark home ranges. The size of the squirrel's home area is related to habitat quality, season, sexual activity and food abundance, and the size of the home area varies greatly in different distribution areas, but usually the male home area is larger than the female, and the dominant individual home area is larger than that of the secondary individual. In food-rich areas, small overlaps occur in the home area.
4. Nesting behavior
Squirrel camp nesting life, you can also use tree holes and bird nests. Each individual usually occupies 2 to 3 nests at the same time. Since the branches and leaves of the fir trees are denser than those of pine trees, in plantations, squirrels usually choose to nest on the fir trees. Nest site selection in natural forests has not been reported. Most of the nests are built on branches 8 to 16 m above the ground, near the trunk or at the fork of the branches, divided into two types of rest nests used during the day and sleep nests used at night, usually spherical in shape, about 30 cm in diameter, the outer layer is made of twigs, pine needles and leaves, the inner diameter is about 12 to 16 cm, covered with soft materials such as moss, leaves, pine needles, hay and bark. In the winter, a microclimate environment is formed in the nest of squirrels, and the temperature can be 20 to 30 ° C higher than that outside the nest, thereby reducing the energy consumed by the body's body temperature regulation and reducing the time exposed to low temperatures and winds outside the nest, which is one of the winter survival strategies of squirrels living in the northern temperate region. In the cold winter, there will also be several squirrels sharing the same nest to maintain body temperature.
5. Reproduction behavior
The reproductive status of squirrels is closely related to the status of food acquisition. It is possible to have two births per year, mating in February, March and July and August, with a gestation period of about 38 to 39 days. But if food is not available, spring mating can be delayed or disappeared. The marriage system is a one-male poly-female system or a mixed mating system. There is courtship behavior before mating, and usually the dominant male will have more mating opportunities. Newborn female rats usually begin to give birth in the second year, and their reproductive ability is closely related to body weight, only female squirrels that exceed a certain weight threshold have fertility, and the larger the weight, the more offspring can be produced. The pups are fed alone by female rats for a period of more than 10 weeks of lactation.
Migration and diffusion
Squirrels do not migrate significantly, but have short-range spread behavior, including outward spread from the wintering ground and outward from the place of birth. Local competition determines the current status of population squirrel ecology and the prospective diffusion distance. Studies have shown that different sexes differ in the spread season, with most male individuals spreading in the spring, while females usually spread in the fall. The spread of female individuals is affected by food, while the spread of males depends on the distribution of females.