Rhombomys opimus

The typical feature is that there are two obvious longitudinal grooves on the upper incisors, which distinguishes it from the members of the genera Short-eared Gerbil and Gerbil. The body length is slightly larger than that of the Tamarix gerbil, averaging about 160mm. The tail length is slightly shorter than the body length, averaging about 150mm, which is about 92% of the body length. The ears are relatively short and folded forward and do not reach the eyes. The back of the body is gray-brown to sandy yellow, with gray-black brushes. The buttocks are dark brown, the shoulders are light gray-yellow, the abdomen is gray-white, and the hair base is gray. The throat is white. The base of the tail is the same color, brown-yellow. The back of the tail begins to grow long black hair from the middle, forming a black hair bundle at the end of the tail. The claws are strong and black. The overall hair color is lighter in winter.

In China, it is distributed in Xinjiang, Gansu, Ningxia, and Inner Mongolia. Abroad, it is distributed in Mongolia, Kazakhstan, Afghanistan, Iran, and Pakistan.

The great gerbil lives in sandy deserts, clay deserts, and gravel deserts below 900 meters above sea level, and chooses environments with shrubs such as Haloxylon ammodendron, Tamarix, Saltclaw, and Nitraria as habitats.

Gerbils live in colonies, often active during the day, and do not hibernate. In winter, the daily activity rhythm is unimodal, and its activity range generally does not exceed 2.5m; in summer, it is bimodal. As the temperature rises, outdoor activities gradually decrease. They do not go out at noon, but after dusk, they gradually go out of the cave to move around, with an activity range of 40~50m, and some can reach 300m. Gerbils have a very high ability to return to their nests. Adult rats can generally return to their original burrows within 100 meters, but young rats are far less conservative about their nests than adults.

The hearing and vision of the great gerbil are very sharp, and they are also alert to foreign objects at the entrance of the cave, and they are always accompanied by lookout behavior, which is sometimes difficult to distinguish from alert. When leaving the cave, the great gerbil first sticks its head out, confirms that there is no danger near the cave entrance, and then drills out of the cave, and then stands on the small platform in front of the cave entrance to look out. The action is similar to alerting, but it does not make a whimper. When eating, the great gerbil will look out while eating, and will immediately switch to alert behavior when there is danger. Observation from a distance revealed that the duration of this kind of lookout behavior of the great gerbils is generally not too long, and then they move, eat, play and other behaviors. Its natural enemies include eagles, tiger weasels and foxes.

Great gerbils usually live in groups, often forming quite obvious cave groups. The distribution of cave groups varies with the terrain. The strip-shaped cave groups are distributed along the valleys, ridge-shaped sand dunes, canal sides and both sides of the road, and the length of the longest cave groups can reach several thousand meters; the semi-fixed sand dunes and block-shaped Haloxylon ammodendron forests with no obvious direction are island-shaped cave groups. Each cave group often has a central area, which is not large in area and has excellent natural living conditions. There are often dense cave entrances here, and the caves are connected, and the rat density is the highest. From the central area to the outside, the density decreases with increasing distance. In early spring, there is a pair of breeding mice in a cave system, and in autumn, there may be more than ten. The structure of the cave is very complex. The diameter of the cave entrance is about 6~12cm, and there are 10~30 cave entrances in a cave system. Some have more than 100 cave entrances, and the cave system covers an area of 2~3hm². The caves are intertwined and divided into 2~3 layers. The first layer is about 40cm from the ground, and each layer is 10~30cm apart. There are granaries and toilets next to the caves. The cave entrances that are frequently entered and exited in winter are mostly near the granaries. The old nests are relatively deep, most of which are located 2~3m underground, and there are sleeping mats made of fine grass and soft hair. The nests are divided into summer nests and winter nests. The summer nests are shallower, and the winter nests are between 1.5~2m deep. There is a granary in the expanded part of the cave. They vary in size, and the largest one can store more than 100kg of grass. Abandoned warehouses are often converted into toilets. In areas with soft soil structure, the cave system often collapses naturally. In areas with relatively solid soil, the caves that have been used for a long time often have tall mounds in front of the cave entrances, which are composed of discarded soil, leftover food and other waste; some mounds are as high as 40~60cm and cover an area of 1~2m². Sometimes the mounds are connected to each other, which can change the micro-topography of the habitat.

The giant gerbil is a herbivorous animal with more than 40 kinds of food, mainly Haloxylon ammodendron, Salsola, Pipa Chai, Salt Claw, Nitraria thornii, Equisetum False, Caragana, and Phragmites australis. In winter, they mainly rely on the food stored in summer and autumn to survive the winter, and also eat seeds and plant stems and barks. The great gerbils do not drink water and completely rely on the water in the food to survive.

The great gerbils reproduce from April to September every year, with the peak period from May to July. They produce 2 to 3 litters per year, with a gestation period of 22 to 25 days, and 1 to 12 litters per litter, mostly 5 to 6 litters. Female mice born in spring can participate in reproduction that year. The young mice overwinter in the mother mouse's hole, separate in the spring of the following year and begin to reproduce.

In China, the number of gerbils is often related to food, and the growth of plants in the desert is closely related to the precipitation from October of the previous year to May of the current year. The number of gerbils is proportional to the precipitation during this period. Therefore, the number of gerbils can be predicted based on the precipitation during this period.

Listed in the 2008 IUCN Red List of Threatened Species ver 3.1 - Least Concern (LC).