Detection of rodents at low density

[Dave Houston]

Pete McClelland of Southland recently asked how to detect rodents in low densities (particularly important in places that are supposed to be rodent-free).  Conclusions drawn from the replies he received were;

• Rats will chew anything ! Many food products are good attractants e.g. chocolate, coconut etc but won't last long enough for our purposes (either break down in weather or are totally eaten by rats or inverts).
• You get good incisor marks on soap and wax but doubts on the attractiveness of these substances. i.e. suitability at low densities when there's plenty of natural food.
• The landcare chew cards (corflute with peanut butter) work well but are relatively short term!
• Unbaited/ baited traps give you a carcase but are too bulky to be practical on a large scale!
• The peanut butter flavoured wax tags - either home made or from Pest control research seem to have the most potential - weather well, good attractiveness (theoretically anyway since I can't find any trials at low density) and easy to put out and check in large numbers.

Anyone else have comments on the subject?  Could be a good topic for a wiki page.

[Dave Houston]

Bill Flury has just pointed out a paper in the NZ Journal of ecology that discusses the use of artificial eggs and clay eggs to detect predator activity.

Using artificial nests to predict nest survival at reintroduction sites
Rebecca M. Lewis, Doug P. Armstrong, Michael K Joy, Yvan Richard, Don Ravine, Åsa Berggren and Rebecca L. Boulton

Currently in press but can be found here

[Steptoe]

good attractants e.g. chocolate, coconut etc but won't last long enough for our purposes (either break down in weather or are totally eaten by rats or inverts).

Around our avairys is a constant maintaince program with traps etc...othen going months without a 'hit'

A mix of peanut butter/ coco, and in a thick solid paste of dripping for autumn to spring....summer it tens to melt down, then dry out a bit.

Then ther is the old 'trap'  a bucket of water with polystreene bits floating, a stick up to the center of the bucket ....vermin runs up the stick following the smell, sees the bait , cant see the water, jumps in and drowns....

[Andy Hutcheon]

Peanut butter wax tags (at least at Macraes) are attractive to a variety of invertebrates (weta, crickets/grasshopers, caterpillars and perhaps others). These can remove large amounts of material, and leave markings that are hard to distinguish, with the naked eye, from mouse chew. Magnification reveals the lack of distinctive twin incisors, and with practice you can differentiate with the naked eye after a bit of squiniting and staring most of the time.

Two problems:

Not quick and easy to check.

May lose rodent sign if the inverts turn up afterwards, if tags are left out long term.

[Dave Houston]

It's interesting that Macraes invertebrates like chewing on wax tags - on Rangatira Island where the density of invertebrates such as weta is astounding, the only thing chewing the tags so far have been parakeets.

We also put tracking tunnels out from time to time but they are not very effective as the weta clean up the bait within an hour or two of it getting dark.

[Malcolm Thomas]

Kara Pankerd from the Rotokare Scenic Reserve Trust in Taranaki has been using WaxTags to detect rodents in their Xcluder fenced 230 hectare reserve. She was doubtful about some deep grooves in WaxTags and sent me some samples. I sent them back as mouse bite marks but was a bit dubious about their rounded corners and lack of chisel like form as made by incisors. Kara put a WaxTag in a tracking tunnel and confirmed that the marks were in fact made by weta. Learning curve for me as one who is focused on vertebrate pests and not insects.