Nest build fresh nests daily out of leaves and other vegetation in which they sleep at night. They sometimes also build nests during the day for resting in. The smaller species of gorilla build their nests in trees, while the larger are confined to the ground. Nests of the western gorilla, the largest species, measure about in diameter. Some species of frog build nests ranging from simple to modest complexity. Many stream-dwelling frogs lay their eggs in a gelatinous mass which they attach to underwater vegetation. The jelly structure prevents the eggs from washing away. Fish engage in nest building activities
Menstruation (mammal) elephant shrew. Females of other species of placental mammal undergo estrous cycles, in which the endometrium is completely reabsorbed by the animal (covert menstruation) at the end of its reproductive cycle. Many zoologists regard this as different from a "true" menstrual cycle. Female domestic animals used for breeding —for example dogs, pigs, cattle, or horses— are monitored for physical signs of an estrous cycle period, which indicates that the animal is ready for insemination. Females of most mammal species advertise fertility to males with visual behavioral cues, pheromones, or both. This period of advertised fertility is known as "oestrus", "estrus"