Performing predator surveys is crucial for Tiakina Whangārei and our mission to create a predator-free Whangārei. We first need to understand the problem and to do this we conduct thorough surveys throughout our city with the help of our wonderful community.
Mammalian predator surveys were conducted at 15 sites across Whangārei in late September and October 2020 to help paint a picture of where they are and their relative abundance. The Tiakina Whangārei team surveyed 12 sites around the city and NorthTec Environmental students surveyed an additional three sites in the Parihaka Reserve.
Two methods were used to detect and estimate the abundance of predators:
This method was developed by the Department of Conservation. 10 tunnels are spaced out over a transect. Each tunnel has a card with ink in the middle. The edges are baited with peanut butter and whatever runs through leaves footprints. The abundance for each species is calculated from the per cent of tunnels on each transect that are tracked. This method is used for estimating rodent abundance. This survey is done over one night.
This method was developed by Manaaki Whenua – Landcare Research. A card is a small rectangle of plastic corflute that has a tasty peanut lure injected between the layers. They are folded at right-angles and nailed to trees about 30cm above the ground. Animals can be identified from their bite marks. There are also 10 on a transect and this method was specifically designed to detect and estimate the abundance of possums. Abundance is calculated the same as above. This survey is done over seven nights.
The sites we surveyed were in a mix of forest areas, along urban waterway and around mangrove edges. As these were all in Whangārei, the sites were generally close to residential or industrial areas.
Predator control was not occurring at any site surveyed (the Parihaka sites were in areas not managed by the local Parihaka Landcare Group).
Not surprisingly, the results showed that possums were most abundant in areas associated with trees, however, it was not just the larger forest fragments like Parihaka that detected this species. At the Denby Golf Course, 80% (8/10) of cards had possum interference. Also, in the sites adjacent to mangrove forests (like the Waimahanga Track in Onerahi; Kioreroa Road) possums were fairly abundant too. This leads to more questions about how possums use mangrove forests – do they hang around the edges or are they all through them? This is especially interesting for areas like Onerahi where there is a lot of mangrove forest edging the suburb.
Rats were abundant in forests like Parihaka but also common around the urban waterways, like the Waiarohia Stream (adjacent to Western Hills) and the Tawera Stream in the CBD. Interestingly, the stream behind Jubilee Park where we did some trapping for rats a month before the survey, detected very low numbers of rats. This suggests that control in sites like this can have impacts on the rat population.
It was interesting that some of the stream sites that detected rats were not surrounded by what is generally classed as a ‘good’ rat habitat. For example, the Hatea River site was adjacent to Hatea Drive before town and the Waiarohia Stream. This may suggest that these water bodies are corridors for rats to move along, which would allow them to safely penetrate the CBD and residential areas. We will focus on targeting these areas in 2021 as this could potentially have large impacts on the rat population – watch this space!