Is agile wallaby management an oxymoron?

Wildlife management specialist Brett Ottley spoke at a recent field day about agile wallaby management.

In tropical savannas “Macropod densities are generally low (< 0.5 animals km²)…There maybe high grazing pressure from some species (e.g. agile wallaby) in localised areas, such as river frontages (Fisher et al 2004, p29).”

I suggest that in some agricultural situations, particularly on river frontages, where there is abundant water and protein and no population control, 1000 times the number above is not unrealistic. Brett suggested that for every wallaby he saw, there was another 15 nearby. Or at dawn and dusk when they are most active, only about 15-20% would be visible at any one time. Individuals come out and feed for a short time then go back into cover.

The fundamental problem with wallaby management is that there’s not a lot known about them. As a pest there has been little research, so it’s hard to devise management programs to address issues.

For example, the relationship between the number of pests and the impact they cause is unlikely to be linear. Impacts may be reduced sufficiently with minor culling, or only after most of the population is culled. Knowledge of this relationship is a critical part of understanding what needs to be done and the likely cost. But we don’t know how many wallabies would need to be culled to reduce impacts (revisit impacts here).

The effort to get a regional population down to manageable levels with shooting appears too costly. And when the scent of neighbouring animals disappears following a cull, others will migrate into that area where resource availability is now high, increasing survivorship.

So could a scent be used to fool wallabies and keep them away from culled areas? Possibly, but Brett told us how quickly wallabies learn, almost overnight, about what’s going on around them and how to respond. They can learn to cross cattle grids. They avoid open areas if control pressure is high. They remember and react to the shooting methods even where it hasn’t been applied for 12 months. Brett suggested that most people don’t get numbers down enough to discover how smart and wary they can become.

Brett believes that dogs are a significant predator of wallabies and discussed research that he conducted where scats collected from dogs often contained agile wallaby hair. Stopping culling of wild dogs is not an option for most pastoralists, but it does suggest that dogs trained to avoid calves and operated over several properties could be beneficial (e.g. Merrema dogs).