Shrew

Shrews are approximately 200 to possible 290 species of small animals constituting the family Soricidae in the order insectivora. They are like a rat in general appearance but have longer, pointed snouts, small ears, and tiny eyes. Their fur is short and dense and usually brown or gray in color. Shrews are found in North and Central America and the extreme northwestern tip of South America, in Eurasia, and in Africa. Most are terrestrial and commonly live near stream or other moist sites. Some species called water shrews are aquatic.

Shrews are the smallest of all living mammals, ranging in size from Savi's pygmy shrew, Suncus entruscus, of Eurasia, which is 60 to 80 mm (2.4 to 3.1 in) long, including its tail, and 1.5 to 2 g (0.05 to 0.07 oz) in weight, to the rat sized. African forest shrew, Praesorex goliath, which reach 290 mm (11.4 in) in length its tail.

Because of high metabolic rate, shrew must normally eat about two-thirds of their body weight in food each day; under certain conditions, such as when the female is nursing young, this intake may be much higher. Shrews feed mainly on insects but commonly take a wide variety of animal foods.

The elephant shrews are mouse to rat size mammals of the family Macroscelididae in the order insectivora. They have long, somewhat flexible snouts, large eyes, and long hind legs. The 16 to 28 species are native to Africa, where they are found from open plaints to forest.

The other shrews are 3 species of aquatic African insectivores classified either as a subfamily of the tenrecs, family Tenrecidae, or as a family of their own, Potamogalidae. They are the largest of the insectivores, the giant otter shrew, Potamogale, reaching about 60 cm (2 ft) in length, almost half of which is the powerful tail.

Rat Mating

Among complex land animals, an elaborate courtship is usual, but rats and other small animals are exceptions. Nevertheless, there is a large literature on the matting behavior of rats, surveyed by Beach, Bolles, Hinde and Larson. When references are not given below, they should be sought in these reviews.

If an adult male, recently deprived of female company, encounters a female be approaches and sniffs her, he may sniff and lick her genitalia, or he may omit this formality and try to mount her. If the female is not in entrus, she does not allow intro-mission: typically she kicks the male off, but she may merely walk away. If the female is in entrus she may herself take the initiative in approaching the male and nosing him. After the first contact she runs a short distance, and pauses; the male follows and mounts her; as the male presses on the female's flanks, she adopts a posture which permits intro-mission, with the coccygeal region raised and the tail to one side. The male performs pelvic thrusts and, if ejaculation does not occur, then leaps backwards. The whole contact takes only a few seconds. If ejaculation occurs, the male does not leap back, but pauses and then usually falls off to one side of the female.

In a typical encounter, about five initial intro-missions occur at short intervals without ejaculation; on the sixth, the female is inseminated, and there is then a refractory period of a few minutes is inseminated; and there is then is refractory period of a few minutes, after which the sequence is repeated, but with fewer preliminary intro-missions before ejaculation. The refractory period lengthen, but ejaculation occur progressively earlier one intro-missions have been resumed. There is consequently an apparent anomaly as the readiness to copulate declines, the readiness to ejaculate increases.

This behavior is characteristic of the whole species Rattus norvegicus; it has been observed in various laboratory strains and much of it also among wild rats. It differs substantially from the mating of some other rodents: the male guinea pig (Cavia) may rest for more than one hour after a single ejaculation. Whatever the species, the whole sequence is highly stereotyped; the typical behavior of each sex provides a clear example of a fixed action pattern.