Kangaroos are best known for having pouches that house their developing offspring (called joeys), but that's not the only interesting feature of their reproduction.
Kangaroos are capable of breeding all year-round, though most mating occurs in late spring and early summer. The marsupials typically live in small groups; during the peak breeding months, they come together and form larger mobs that congregate around resources, such as food, water and access to females.
The animals show extreme sexual dimorphism, with males growing to be several times the size of females, said Bill Bateman, a wildlife biologist at Curtin University in Australia. Male kangaroos also develop very large muscles in their upper body, which they sometimes show off by striking poses.
"The females, in turn, may be able to use the big muscles as a way of judging the quality of the males available and preferentially encourage mating with the big guys," Bateman told LiveScience.
A male can tell if a female is in heat and ready to mate by sniffing or tasting her urine — he may even encourage her to urinate by pawing at her tail and face, calling softly or rubbing her urogenital opening.
But males are highly competitive over females and battles are common.
To start the sensual act, "a male will rub his chest on the grass or some bushes, growl and cluck as he stands up onto his toes and tail tip," said biologist Emily Miller of the University of Sydney in Australia. The other male will either bow low and cough (signifying he declines the challenge) or fight back, resulting in a violent boxing match that usually ends when the loser runs away.
After a male has won access to a female, he will grab her at the waist from behind with his powerful arms, hold her still and mate with her for up to 50 minutes. "She often carries on grazing, it’s not very romantic," Bateman said.
Interestingly, females have three vaginas — two for sperm and one in the middle for birthing. Males have long, double-headed penises to inseminate the lateral vaginas. [The 7 Weirdest Animal Penises]
Copulation complete, the male will guard his female for a few hours to make sure other males don't mate with her, too, Miller told LiveScience. He will then leave to mate with other females in his mob.
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