Both male and female kangaroos can breed at any time of the year. Females are ready to mate again a few days after they give birth. Males can check if the female is receptive by smelling her urine. Mating is often quick, often lasting 15 minutes. Although they generally give birth to one offspring at time, females can have offspring at different development stages at the same time, because they have a pouch that can keep more than one animal.
Kangaroos have short gestation periods, which last for about 33 days. This can vary slightly according to species. Although the developmental stage in the womb is short, newborns spend about 70 days without leaving the pouch, where they finish their development. Young kangaroos are about one inch long when born but they have limbs adapted to crawl up the mother's body, reaching her pouch, where it attaches itself to a tit.
Kangaroos are marsupial animals because the females have an organ called marsupium or pouch, where they keep their underdeveloped newborn young. Although still embryos at birth, kangaroos have strong jaw muscles, limbs and tongues. After living the pouch for the first time, young kangaroos still come back to the pouch to feed for about one year.
Although females are sexually receptive and can mate soon after they give birth, the development of a new embryo is stopped at ans early stage. The embryo remain dormant inside the womb until her other young is permanently attached to the tit, in the pouch. Only when the pouch is vacated, the dormant embryo continues to develop. This phenomenon is called embryonic diapause. Female also have two vaginae, both functional for mating.
At birth, the two vaginae fuse to form a birth canal.