Are Australia's mysterious mammal declines spreading?

ALERT has previously reported on the enigmatic and alarming population declines of mammal species across northern Australia.  Now, it appears the declines could be even more widespread than previously suspected.

Bye-bye beautiful bettong?

Bye-bye beautiful bettong?

To date, the declines of smaller and medium-sized mammals, such as quolls, bandicoots, and native rodents, have been mainly documented in monsoonal forests and woodlands across Australia's top end -- such as those at Kakadu National Park, where the declines have been best studied

Additional research -- including interviews of Aboriginal communities in remote areas of northern Australia -- have shown the declines to be widespread in nature, extending over many thousands of kilometers. 

Now, recent research -- which has yet to be published -- suggests that the declines might even extend to northeastern Australia, to the wet tropical region of far north Queensland. 

In this area, live-trapping and camera-trap studies by Sandra Abell-Davis of James Cook University suggest that the tropical bettong, an endangered wallaby-like marsupial, may also be declining sharply.

Abell-Davis studied three areas that had formerly been live-trapped for the bettongs, using identical trapping methods.  She found that, on average, bettong numbers had fallen by more than 80%.

Abell-Davis emphasizes that her findings, while alarming, are still provisional.  She wants to trap more extensively for the bettong and use novel genetic analyses, to see if its numbers have fallen elsewhere in the region.  In fact, she is looking for volunteers to help with this important field work. 

A number of possible drivers have been suggested for northern Australia's mammal declines, with feral cats and altered fire regimes being among the leading suspects

Other suggested possibilities include foreign pathogens, changing rainfall regimes, overgrazing, foxes, and the introduced cane toad, which produces toxins deadly enough to kill virtually anything that eats it.

Whatever is going on, it raises frightening prospects for an Australian continent that has already suffered massive extinctions of its native mammals.

The mystery of Australia's small mammal declines

Across the top end of Australia, from Cape York to the Kimberly Mountains, populations of smaller marsupials and native rodents are collapsing.  What's going on?

Tapping into traditional knowledge to help solve a mystery (photo by Ian Morris)

Tapping into traditional knowledge to help solve a mystery (photo by Ian Morris)

Several studies in recent years have documented the declines.  A few have shown major changes in a single location, such as Kakadu National Park.  Others have compiled scattered information over a much broader area; one innovative study used interviews with Aboriginal communities to piece together evidence (find study here).

The bottom line: many species that used to be common have become vanishingly rare, or have geographic ranges that are collapsing. 

What is causing all this?  No one is sure.  Some suspect it could be severe overgrazing by livestock, especially during droughts.  During such times the vegetation can become badly damaged--as we're seeing at present in many areas

Others think altered fire regimes are the cause.  And yet others suspect predation by feral cats, with a possible role for lethal cane toads for certain predatory mammals.

Whatever the cause, this might be a new biodiversity crisis for the Land Down Under, which has already lost more native mammal species than any other continent.