in motion grazing s
Locomotion Kangaroos are the only large mammals to use
hopping on two legs as their primary means of
locomotion. The comfortable hopping speed for a red kangaroo is about , but speeds of up to can be attained over short distances, while it can sustain a speed of for nearly . During a hop, the powerful
gastrocnemius muscles lift the body off the ground while the smaller
plantaris muscle, which attaches near the large fourth toe, is used for push-off. Seventy percent of potential energy is stored in the elastic tendons. At slow speeds, it employs pentapedal locomotion, using its tail to form a tripod with its two
forelimbs while bringing its hind feet forward. Both pentapedal walking and fast hopping are energetically costly. Hopping at moderate speeds is the most energy efficient, and a kangaroo moving above maintains energy consistency more than similarly sized animals running at the same speed.
Diet Kangaroos have single-chambered stomachs quite unlike those of
cattle and
sheep, which have four compartments. They sometimes regurgitate the vegetation they have eaten, chew it as
cud, and then swallow it again for final digestion. However, this is a different, more strenuous, activity than it is in
ruminants, and does not take place as frequently. Different species of kangaroos have different diets, although all are strict
herbivores. The eastern grey kangaroo is predominantly a
grazer, and eats a wide variety of grasses, whereas some other species such as the red kangaroo include significant amounts of
shrubs in their diets. Smaller species of kangaroos also consume
hypogeal fungi. Many species are
nocturnal, and
crepuscular, usually spending the hot days resting in shade, and the cool evenings, nights and mornings moving about and feeding.
Absence of digestive methane release Despite having herbivorous diets similar to
ruminants such as cattle, which release large quantities of digestive
methane through
exhaling and
eructation (burping), kangaroos release virtually none. The
hydrogen by-product of
fermentation is instead converted into
acetate, which is then used to provide further energy. Scientists are interested in the possibility of transferring the bacteria responsible for this process from kangaroos to cattle, since the
greenhouse gas effect of livestock methane is a significant contributor to anthropogenic climate change.
Social and sexual behaviour s boxing Groups of kangaroos are called
mobs,
courts or
troupes, which usually have 10 or more kangaroos in them. Living in mobs can provide protection for some of the weaker members of the group. with eastern Australia having larger and more stable aggregations than in arid areas farther west. The kangaroo performing the sniffing gains much information from smell cues. This behaviour enforces social cohesion without consequent aggression. In mutual sniffing, a smaller kangaroo may crouch and quiver its head as a sign of submission. A male will monitor a female and follow her every movement. He sniffs her urine to see if she is in oestrus, a process exhibiting the
flehmen response. The male will then proceed to approach her slowly to avoid alarming her. Another defensive
tactic described by witnesses is catching the attacking dog with the forepaws and
disembowelling it with the hind legs.
Adaptations Kangaroos have developed a number of adaptations to a dry, infertile country and highly variable climate. As with all
marsupials, the young are born at a very early stage of development—after a
gestation of 31–36 days. At this stage, only the forelimbs are somewhat developed, to allow the newborn to climb to the
pouch and attach to a
teat. In comparison, a human
embryo at a similar stage of development would be at about 7 weeks gestation (even in a modern intensive care unit,
premature babies born at less than 23 weeks gestation are usually not mature enough to survive). When the joey is born, it is about the size of a
lima bean. The joey will usually stay in the pouch for about 9 months (180–320 days for the Western Grey) before starting to leave the pouch for small periods of time. It is usually fed by its mother until reaching 18 months. The female kangaroo is usually pregnant in permanence, except on the day she gives birth; however, she has the ability to freeze the development of an embryo until the previous
joey is able to leave the pouch. This is known as
embryonic diapause and will occur in times of drought and in areas with poor food sources. The composition of the milk produced by the mother varies according to the needs of the joey. In addition, the mother is able to produce two different kinds of milk simultaneously for the new-born and the older joey still in the pouch. Unusually, during a dry period, males will not produce sperm and females will conceive only if enough rain has fallen to produce a large quantity of green vegetation. The male has numerous
sweat glands on the
scrotum and a strong
cremaster muscle that retracts the
testes toward the body wall in order to regulate their temperature. The
penis is retracted into a preputial sac which is everted through the
cloaca. Kangaroos and wallabies have large, elastic tendons in their hind legs. They store elastic strain energy in the
tendons of their large hind legs, providing most of the energy required for each hop by the spring action of the tendons rather than by any muscular effort. This is true in all animal species which have muscles connected to their skeletons through elastic elements such as tendons, but the effect is more pronounced in kangaroos. There is also a link between the hopping action and breathing: as the feet leave the ground, air is expelled from the lungs; bringing the feet forward ready for landing refills the lungs, providing further energy efficiency. Studies of kangaroos and
wallabies have demonstrated, beyond the minimum energy expenditure required to hop at all, increased speed requires very little extra effort (much less than the same speed increase in, say, a horse, dog or human), and the extra energy is required to carry extra weight. For kangaroos, the key benefit of hopping is not speed to escape predators—the top speed of a kangaroo is no higher than that of a similarly sized quadruped, and the Australian native predators are in any case less fearsome than those of other countries—but economy: in an infertile country with highly variable weather patterns, the ability of a kangaroo to travel long distances at moderately high speed in search of food sources is crucial to survival. New research has revealed that a kangaroo's tail acts as a third leg rather than just a balancing strut. Kangaroos have a unique three-stage walk where they plant their front legs and tail first, then push off their tail, followed lastly by the back legs. The propulsive force of the tail is equal to that of both the front and hind legs combined and performs as much work as what a human leg walking can at the same speed. A
DNA sequencing project of the
genome of a member of the kangaroo family, the
tammar wallaby, was started in 2004. It was a collaboration between Australia (mainly funded by the
State of Victoria) and the
National Institutes of Health in the US. The tammar's genome was fully sequenced in 2011. The genome of a marsupial such as the kangaroo is of great interest to scientists studying
comparative genomics, because marsupials are at an ideal degree of evolutionary divergence from humans:
mice are too close and have not developed many different functions, while birds are genetically too remote. The dairy industry could also benefit from this project.
Blindness Eye disease is rare but not new among kangaroos. The first official report of kangaroo blindness took place in 1994, in central
New South Wales. The following year, reports of blind kangaroos appeared in Victoria and South Australia. By 1996, the disease had spread "across the desert to Western Australia".
Veterinarians also discovered fewer than 3% of kangaroos exposed to the virus developed blindness.
Reproduction and life cycle Kangaroo reproduction is similar to that of
opossums. The egg (still contained in the shell membrane, a few micrometres thick, and with only a small quantity of yolk within it) descends from the
ovary into the
uterus. There it is fertilised and quickly develops into a
neonate. Even in the largest kangaroo species (the
red kangaroo), the neonate emerges after only 33 days. Usually, only one young is born at a time. It is blind, hairless, and only a few centimetres long; its hindlegs are mere stumps; it instead uses its more developed forelegs to climb its way through the thick fur on its mother's
abdomen into the pouch, which takes about three to five minutes. Once in the pouch, it fastens onto one of the four teats and starts to feed. Almost immediately, the mother's sexual cycle starts again. Another egg descends into the uterus and she becomes sexually receptive. Then, if she mates and a second egg is fertilised, its development is temporarily halted. This is known as
embryonic diapause, and will occur in times of drought and in areas with poor food sources. Meanwhile, the neonate in the pouch grows rapidly. After about 190 days, the baby (
joey) is sufficiently large and developed to make its full emergence out of the pouch, after sticking its head out for a few weeks until it eventually feels safe enough to fully emerge. From then on, it spends increasing time in the outside world and eventually, after about 235 days, it leaves the pouch for the last time. The
lifespan of kangaroos averages at six years in the wild to in excess of 20 years in captivity, varying by the species. Most individuals, however, do not reach maturity in the wild. == Interaction with humans ==