A recent spate of “drunken” kangaroos staggering around Victoria, Australia, may have a slightly more sinister cause. It has been suggested that the disorientated and intoxicated marsupials are in fact showing signs of having eaten a poisonous grass that's causing neurological damage.

Wildlife charities and vets in the state have reported a sudden increase in members of the public describing grey kangaroos in the region acting as if they are drunk. However, it seems that the most likely culprit is not a sneaky tipple, but an invasive species of grass known as Phalaris aquatica.

Known to contain neurotoxins, the grass can cause “phalaris staggers” in the kangaroos that eat it, resulting in head tremors, staggering, and collapsing as the animals lose motor function.  

“A kangaroo with full-blown toxicity is just horrible,” Manfred Zabinskas, who works for Five Freedoms Animal Rescue, told Guardian Australia. “Their head flies around like they have got a broken neck; they summersault; they crash into fences and trees… they look like they are drunk.”

The plant is not actually native to southeastern Australia, but was introduced as a pasture crop by farmers. Due to its ability to cope with high salinity, its impressive root system that stabilizes the earth and prevents wind erosion, and its drought tolerance, it has long been popular despite its toxicity.

Even though the plant can and does cause phalaris staggers in domestic animals such as sheep and cattle, historically farmers believed the benefits of the plant outweighed the costs, as they were able to treat the livestock by introducing copper into their diet and moving them on to pasture that does not contain the grass. In more recent times, farmers have moved away from using the plant.

But unfortunately, it is now well-established in parts of Victoria, and there is no one to help the wild kangaroos when they eat the grass. Instead, because the condition is pretty much irreversible, the most humane thing to do is to euthanize the marsupials, otherwise they risk being attacked by wild dogs or foxes.

Whether or not they are genuinely suffering from the poisoning has yet to be confirmed, although researchers at Melbourne University are currently running tests. It has been suggested that a bumper year for the grass may be behind the sudden spike in kangaroos falling ill.

If anyone spots an unfortunate kangaroo suffering from the illness, they are encouraged to report it to the local government before calling wildlife charities.