Barking up the wrong tree?

3 November 2020

Bark damage is often a clearly visible animal pest sign but identifying the culprit is not always easy – as Roger Young found at his property on the outskirts of Christchurch.

After returning from holiday earlier this year, Roger was dismayed to see a lot of damage on some lowland ribbonwood (Plagianthus regius) trees in his restored wetland. He at first suspected possums because they had repeatedly stripped bark from gum trees elsewhere on his property and he had trapped a good many in that area. Normally, he would have been checking his property daily and would have noticed the damage before it became so extensive.

As soon as he noticed the ribbonwood damage, Roger moved his entire arsenal of possum and rat traps to the vicinity and resumed his normal routine of daily trap checking. From the results, he concluded that rats had probably inflicted the damage rather than possums.

“There was no sign of possum scat near the ribbonwood and there was what looked like the marks of a rat’s front incisor teeth where the bark had been stripped. There are lots of mature cabbage trees on that side of the wetland and the rats love living amongst the old fronds. I’ve previously caught them there but never possums.

“When I put out the extra traps in the wetland, I didn’t catch any possums but got a huge ship rat the very next morning. There’s been no more damage since!”

Roger sent photos of the bark damage to Pest Detective and we consulted some expert advisors. They thought it looked more like possum than rat damage, though the evidence was not conclusive. The clues they considered were:

	Clues that point to possum	Clues that point to rat
Diet	Possums commonly eat bark (often for territorial marking)	Bark is uncommon in rat diet
Claw marks		Claw marks would be expected if possums had done the damage but none were seen
Amount of damage	Larger areas of bark had been than would be expected of rats
Style of damage	The large rough tears and stringy tags were typical of possum damage – they tend to strip off bark by tearing rather than gnawing (as rats would do)
Tooth marks	Looked too big for rat
Trap catch	None caught	Rat caught nearby

Roger is keen to install a camera to identify and target pest animals more precisely in future. He and his wife Kaye started restoring their 1.5-hectare ephemeral wetland in 2014 by planting 5,000 native plants and pest control soon followed, as Roger recalls.

“In 2015, we started trapping around the wetland to make a ‘safe haven’ for native birds and wildlife. I have kept a trap record sheet and, now, five and a half years later, the critter tally is 920. We now enjoy resident bellbirds, fantails and wax eyes, have had nesting king fisher, little owl and pied stilt and hope regularly visiting kereru will take up residency.”

The need to protect this flourishing safe haven keeps Roger out every day checking his traps and looking for pest animal sign.