by Abbie Krause
Jump for joy!
No baby shower, announcement or even a baby bump. Plus, Dad had moved out months earlier. So imagine the surprise of zookeepers when little joey made his appearance at the Pueblo Zoo! While this may catch humans off guard a little, the reproductive process of kangaroos is quite unique and fascinating. The process is constant and adaptable to conditions which helps ensure the survival of the species. A mother may be supporting three babies at different stages at any given time – one developing in utero, one in the pouch and one suckling outside of the pouch. Sounds exhausting!
The red kangaroo is an opportunistic breeder, meaning that it is able to breed year-round when conditions are favorable, but often ceasing reproduction during a drought. Though the female red kangaroo is able to become pregnant again within days of giving birth, the fertilized egg only develops to the blastocyst stage and it then goes into a suspended waiting period know as embryonic diapause until its turn comes to fully develop and take up residence in the pouch. When the suckling joey in the pouch reaches about 200 days old, dies or is removed, the embryo in the uterus resumes its development. The new joey is born around 31 days later, within about a day of the first young one permanently leaving the pouch. The baby is about the size of a jelly bean and it climbs unaided through the mother’s fur into the pouch where it attaches to a teat for the next 70 days of development. At about 150 days of development the young joey begins to pop its head out and will venture out for short exploration at about 190 days. It will permanently leave the pouch at 235 – 245 days. All this time, there may be another joey still nursing outside the pouch and another undeveloped one lying in wait. At this pace, a female kangaroo may produce three offspring in only two years!
Knowing a bit more about the process, helps explain the puzzle at the Pueblo Zoo of how the birth of a kangaroo might sneak up even after any male is in the exhibit.
FACT BOX by Greg Rohr
Scientific name: Macropus rufus. Macropus means “long foot.”
Common name: red kangaroo
Description: Being the largest marsupial, kangaroos can stand four feet tall and weigh up to 120 pounds. They have two long hind legs, which they use to hop and for defense. The powerful, enlarged hindquarters enable the familiar leaping mode of locomotion, and the red kangaroo may be able to reach top speeds of up to 40 miles per hour. When threatened, the kangaroo will lean back on its tail and kick with elongated claws. Males tend to be red, while females typically have a blue-hued coat. Red kangaroo’s coloring helps them blend in to the red dirt of the outback in Australia to escape predators. Both have lighter colored underbellies. A male red kangaroo is also much larger and more powerfully muscled than the female, with larger shoulders and forearms, more heavily clawed forepaws, and thickened skin over the belly, which helps absorb the impact of kicks during fight. In the wild, kangaroos live in small groups (5-10) called mobs. When there is more food available, the groups will be larger. A larger group of animals aides in seeing potential predators more effectively than single or paired animals. Males will fight over territory and the right to mate with the females in their mob. During the heat of the day, kangaroos are often found in shade, usually under trees. To keep cool, they will lick their forearms and other body parts.
Diet: herbivorous: the foundation of a red kangaroo diet consists of plenty of grass in different varieties, shrubs, flowering plants and foliage.
Range: kangaroos are distributed throughout the arid regions of mainland Australia, excluding the extreme north, east coast, and extreme southwest of the country.
Habitat: scrubland, grassland, woodland and desert, tending to prefer open grassy plains with scattered trees for shade and shelter.
Reproduction and rearing: The red kangaroo is an opportunistic breeder, able to breed year-round when conditions are favorable, but often ceasing reproduction during drought. The males engage in ritualized ‘boxing’ in order to gain temporary control of females in estrus, wrestling with the forelimbs around the opponent’s shoulders and kicking with the powerful hind limbs. The female usually gives birth to a single young, after a gestation period of around 32 to 34 days. At birth, the newborn weighs a mere 0.0017 pounds, and takes about three minutes to make its way, unaided, through the female’s fur and into the pouch, where it attaches to a teat for the next 70 days of development. The young, or joey, first protrudes its head from the pouch at 150 days, emerging for short periods at 190 days, and permanently leaving the pouch at 235 to 240 days, although still suckling for another 3 to 4 months . Sexual maturity is reached at around 15 to 24 months.
Lifespan: In the wild, kangaroos live up to 27 years old. In captivity, they can live up to 30 years or more.
Threats: There are no major threats to the red kangaroo, and it remains a widely distributed and abundant species.
Citations: http://www.arkive.org/red-kangaroo/macropus-rufus/