Fauna of Australia species are nocturnal and many arboreal. Two of the five living species of monotreme occur in Australia: the platypus and the short-beaked echidna. The monotremes differ from other mammals in their methods of reproduction; in particular, they lay eggs instead of giving birth to live young. The platypus—a venomous, egg-laying, duck-billed amphibious mammal—is considered to be one of the strangest creatures in the animal kingdom. When it was first presented by Joseph Banks to English naturalists it was thought to be so strange that it was a cleverly created hoax. The short-beaked echidna is similarly strange, covered in hairy spikes
Mammal females mate with (polyandry), or multiple males have exclusive relations with multiple females (polygynandry). It is much more common for polygynous mating to happen, which, excluding [[lek mating|leks]], are estimated to occur in up to 90% of mammals. Lek mating occurs when males congregate around females and try to attract them with various [[courtship display]]s and vocalizations, as in harbor seals. All [[higher mammal]]s (excluding monotremes) share two major adaptations for care of the young: live birth and lactation. These imply a group-wide choice of a degree of [[parental care]]. They may build nests and dig burrows to raise their