Brushtail possums (Trichosurus vulpecula) dominate dama wallabies (Notamacropus eugenii) and Bennett’s wallabies (Notamacropus rufogriseus) at bait feeders: implications for invasive species management

Context

Dama wallaby (Notamacropus eugenii) and Bennett’s wallaby (N. rufogriseus) are invasive pests on the New Zealand mainland and consequently are subject to ongoing control measures that include deployment of toxic baits in feeding stations.

Aim

We investigated whether behavioural interactions between wallabies and introduced brushtail possums (Trichosurus vulpecula) at bait feeders are likely to reduce the efficacy of this method for wallaby control.

Methods

Wallaby and possum visits and encounters at cereal bait feeders were monitored with trail cameras for several months in dama wallaby habitat near Rotorua, and in Bennett’s wallaby habitat in South Canterbury. The response of Bennett’s wallabies to possum carcases placed at feeders was also assessed.

Key results

The diurnal activity of wallabies and possums at the feeders overlapped extensively, although Bennett’s wallabies exhibited more daytime activity than the other two species. Thousands of visits by wallabies and possums were recorded but close encounters between the species at feeders were infrequent (N = 251). When encounters did occur, the wallaby was usually excluded from the feeder (72% of 229 encounters at Titoki Estate, near Rotorua, and 95% of 22 encounters at Blue Cliffs, South Canterbury) regardless of which species arrived at the feeder first. Zero instances of a wallaby excluding a possum from a feeder were recorded. When possum carcases were placed beside feeders, visitations by Bennett’s wallabies reduced significantly, by 86% during the first week when a possum carcase was present. This effect was short lived, however, because the carcase soon decayed or was scavenged by other wildlife.

Conclusions

Despite their smaller body size, possums are strongly behaviourally dominant over both wallaby species. Consequently, possums may empty feeders of bait before visiting wallabies have an opportunity to feed. Furthermore, interruption and exclusion of feeding wallabies by possums will increase the risk of sublethal toxic dosing and consequent bait shyness.

Implications

Since possums are common throughout most wallaby habitat in New Zealand, their dominance behaviour is likely to reduce the efficacy of bait feeder control of wallabies at many sites. Possum population suppression is, therefore, likely to increase the effectiveness of wallaby bait feeder programs but will be costly to achieve.