structural:scholar_edition, stylistic:style_transfer
Reproduction

Females start to breed when they reach sexual maturity, typically in their second year. At this point, they become fertile once a year, producing multiple ova while in heat. As prey is most abundant in spring and early summer, the devil's reproductive cycle starts in March or April so that the end of the weaning period coincides with the maximisation of food supplies in the wild for the newly roaming young devils.

Occurring in March, mating takes places in sheltered locations during both day and night. Males fight over females in the breeding season, and female devils will mate with the dominant male. Females can ovulate up to three times in a 21-day period, and copulation can take five days; one instance of a couple being in the mating den for eight days has been recorded. Devils are not monogamous, and females will mate with several males if not guarded after mating; males also reproduce with several females during a season. Females have been shown to be selective in an attempt to ensure the best genetic offspring, for example, fighting off the advances of smaller males. Males often keep their mates in custody in the den, or take them along if they need to drink, lest they engage in infidelity.

Males can produce up to 16 offspring over their lifetime, while females average four mating seasons and 12 offspring. Theoretically this means that a devil population can double on an annual basis and make the species insulated against high mortality. The pregnancy rate is high; 80% of two-year-old females were observed with newborns in their pouches during the mating season. More recent studies of breeding place the mating season between February and June, as opposed to between February and March.

Gestation lasts 21 days, and devils give birth to 20–30 young standing up, each weighing approximately 0.18–0.24 g (0.0063–0.0085 oz). Embryonic diapause does not occur. At birth, the front limb has well-developed digits with claws; unlike many marsupials, the claws of baby devils are not deciduous. As with most other marsupials, the forelimb is longer (0.26–0.43 cm or 0.10–0.17 in) than the rear limb (0.20–0.28 cm or 0.079–0.110 in), the eyes are spots, and the body is pink. There are no external ears or openings. Unusually, the sex can be determined at birth, with an external scrotum present.

Tasmanian devil young are variously called "pups", "joeys", or "imps". When the young are born, competition is fierce as they move from the vagina in a sticky flow of mucus to the pouch. Once inside the pouch, they each remain attached to a nipple for the next 100 days. The female Tasmanian devil's pouch, like that of the wombat, opens to the rear, so it is physically difficult for the female to interact with young inside the pouch. Despite the large litter at birth, the female has only four nipples, so there are never more than four babies nursing in the pouch, and the older a female devil gets, the smaller her litters will become. Once the young have made contact with the nipple, it expands, resulting in the oversized nipple being firmly clamped inside the newborn and ensuring that the newborn does not fall out of the pouch. On average, more females survive than males, and up to 60% of young do not survive to maturity. Milk replacements are often used for devils that have been bred in captivity, for orphaned devils or young who are born to diseased mothers. Little is known about the composition of the devil's milk compared to other marsupials.

Inside the pouch, the nourished young develop quickly. In the second week, the rhinarium becomes distinctive and heavily pigmented. At 15 days, the external parts of the ear are visible, although these are attached to the head and do not open out until the devil is around 10 weeks old. The ear begins blackening after around 40 days, when it is less than 1 cm (0.39 in) long, and by the time the ear becomes erect, it is between 1.2 and 1.6 cm (0.47 and 0.63 in). Eyelids are apparent at 16 days, whiskers at 17 days, and the lips at 20 days. The devils can make squeaking noises after eight weeks, and after around 10–11 weeks, the lips can open. Despite the formation of eyelids, they do not open for three months, although eyelashes form at around 50 days. The young—up to this point they are pink—start to grow fur at 49 days and have a full coat by 90 days. The fur growing process starts at the snout and proceeds back through the body, although the tail attains fur before the rump, which is the last part of the body to become covered. Just before the start of the furring process, the colour of the bare devil's skin will darken and become black or dark grey in the tail.

The devils have a complete set of facial vibrissae and ulnar carpels, although it is devoid of anconeal vibrissae. During the third week, the mystacials and ulnarcarpals are the first to form. Subsequently, the infraorbital, interramal, supraorbital and submental vibrissae form. The last four typically occur between the 26th and 39th day. Their eyes open shortly after their fur coat develops—between 87 and 93 days—and their mouths can relax their hold of the nipple at 100 days. They leave the pouch 105 days after birth, appearing as small copies of the parent and weighing around 200 g (7.1 oz). Zoologist Eric Guiler recorded its size at this time as follows: a crown-snout length of 5.87 cm (2.31 in), tail length of 5.78 cm (2.28 in), pes length 2.94 cm (1.16 in), manus 2.30 cm (0.91 in), shank 4.16 cm (1.64 in), forearm 4.34 cm (1.71 in) and crown-rump length is 11.9 cm (4.7 in). During this period, the devils lengthen at a roughly linear rate.

After being ejected, the devils stay outside the pouch, but they remain in the den for around another three months, first venturing outside the den between October and December before becoming independent in January. During this transitional phase out of the pouch, the young devils are relatively safe from predation as they are generally accompanied. When the mother is hunting they can stay inside a shelter or come along, often riding on their mother's back. During this time they continue to drink their mother's milk. Female devils are occupied with raising their young for all but approximately six weeks of the year. The milk contains a higher amount of iron than the milk of placental mammals. In Guiler's 1970 study, no females died while rearing their offspring in the pouch. After leaving the pouch, the devils grow by around 0.5 kg (1.1 lb) a month until they are six months old. While most pups will survive to be weaned, Guiler reported that up to three fifths of devils do not reach maturity. As juveniles are more crepuscular than adults, their appearance in the open during summer gives the impression to humans of a population boom. A study into the success of translocated devils that were orphaned and raised in captivity found that young devils who had consistently engaged with new experiences while they were in captivity survived better than young who had not.