Yaminon

BIRD: linking the biodiversity community

Categories: Marsupials | Endangered fauna

Yaminon (Lasiorhinus krefftii), also known as the Northern Hairy-nosed Wombat, is the largest of the three modern wombat species, and probably the rarest large mammal in the world. It is critically endangered, with an estimated 113 individuals remaining.

It is a large, thick-set creature, up to almost a metre in length and weighing between 20 and 32 kg. The fur is soft, shiny, and mid-grey to brownish. Like all wombats, it is nocturnal and crepuscular, spending the day in a deep complex of burrows. Yaminon feeds almost exclusively on native grasses, usually quite close to a burrow entrance, and although as many as 10 Yaminon will share a burrow complex, it is generally solitary. Females give birth to a single young, usually in spring or summer, and in good conditions are able to raise two young every three years.

Apparently never common, it was first described in 1869 from a fossil found in New South Wales. Live Yaminon were not found until 1884. Over time, it became clear that it had occupied parts of northern Victoria, New South Wales and Queensland, but was rapidly declining. Known colonies in southern Queensland, central Queensland, and near Deniliquin disappeared soon after the turn of the century, while the remaining colony (also in the Clermont district of central Queensland, roughly half-way between Longreach and Rockhampton) collapsed to perhaps 20% of its former size.

The reasons for the demise of the southern populations remain unknown, but it seems clear that the primary cause of the northern population's decline was over-grazing in drought years, leaving the wombats to starve.

Preliminary steps to protect the only remaining Yaminon group were not undertaken until 1982, when cattle were excluded from what is now the Epping Forest National Park. The population stabilised and possibly recovered slightly in the following years, and the Queensland National Parks and Wildlife Service instuted a recovery program in 1993.

However, two major threats remained. The tiny patch of suitable remaining habitat is infested with unpalatable African Buffel Grass (Cenchrus ciliaris), leaving less of the native grasses Yaminon prefers to feed on. Secondly, park rangers became aware of a major predation problem. In 2000 and 2001, despite a baiting program, 10% of the Yaminon population was killed by Dingos. To deal with this, a two metre predator-proof fence was constructed around 25 km² of the park in 2002.

Captive breeding and translocation programs, however, have been abandoned for the time being because the population in the sole remaining colony is considered too small to allow the safe removal of the 15 or 20 individuals needed to start a new wild colony, and because more than a decade of captive breeding research with Common and Southern Hairy-nosed Wombats has produced only a handful of successful births.

Researchers at a number of institutions are now working on plans to use Southern Hairy-nose Wombat foster mothers to raise the pouch-young of their northern relatives. It is hoped that this will raise the effective birth rate by allowing Yaminon females to breed more frequently. At this stage, however, there seems to be no answer to the problem of the very small and in-bred gene pool.

Over time, the recovery program aims to build the population up far enough to allow a second colony to be established, which will provide insurance against a single disaster — fire, or infectious disease, for example — wiping the entire population out.