Reproduction in tammars has been intensively studied. Unlike most kangaroos, they have a strictly seasonal breeding pattern.
Unlike most kangaroo species they have a strictly seasonal reproductive pattern. Just after Christmas, tammars sense the decreasing daylength, and trigger growth of the dormant early embryo that they carry in their uterus. This embryo then develops for about 26 days, so in late January most females will give birth. Birth occurs rapidly. A few minutes before birth the mother to be will sit back with her tail between her legs, and vigorously lick her urogenital opening. Soon the fetus is expelled. It breaks free of the embryonic membranes that have surrounded it in the uterus (womb), and it climbs, unaided by the mother, to the pouch, where it sucks one of the teats into its mouth.
A few hours after giving birth the mother will mate. This will produce a new embryo. The fertilised egg develops over the next 8 days to form a hollow ball of about 100 cells called a blastocyst, about a quarter of a millimetre in diameter. Then, whilst there is a sucking pouch young, this embryo is halted (diapause). By the middle of the year, the short daylength of winter provides a seasonal signal that then keeps the blastocyst dormant until after the longest day, when the cycle of embryonic growth and birth resumes.