Citizen Science 2021 - Chew Card Results


Thank you to all those who were involved in the chew card campaign this year!



Link to the running pest abundance maps from 2017 to 2021. Please open this document to have a look at the maps and graphs generated from this year's campaign.


For a more in-depth look at most of our graphs and takes from this years campaign, as well as comparisons to previous years of data, please follow this link here.


For those of you who are new to the chew card campaign, our survey places out corflute cards impregnated with a non-toxic paste along survey lines in over 43 reserves in Kaipātiki. Rats, mice, possums, hedgehog, stoats and even other creatures like dogs and cats leave distinctive marks for us to identify. The results from the campaign allow an in-depth look at where pest control is needed the most, or where an increased diversity of traps is needed. We can also look at more interesting trends, such as how reserves are going over the whole 5 years of the campaign.


We also talk a lot about ‘relative abundance’ (RA). RA is a percentage composition of an organism (i.e a rat) relative to the total number of them in an area. It isn’t an exact count, but does give us a sound scientific base to monitor the prevalence of pests in an area. The LOWER the RA the better as it indicates little to none of that animal in the environment monitored. In general, restoration projects ultimately aim for 5% RA or lower. At this level, many forms of flora and fauna have the best chance for success.


Using these relative abundances we can create some graphs that show each individual pest species impact on different reserves.



Understanding ‘Relative Abundance’


Most of the results below are based on ‘Relative abundance’ which is a percentage composition of an organism of a particular kind, relative to the total number of organisms in the area. It isn’t an exact count, but does give us a sound scientific base to monitor the prevalence of pests in an area.

An example of this in action – is, if you place out 10 chew cards (at the proper spacing), and 7 of them come back with a rat chew, and 2 of them with mice chew, and none with possum chews your relative abundances would be:


Rats: 7/10 = 0.7 or 70%

Mice: 2/10 = 0.2 or 20%

Possum: 0/10 = 0 or 0%


The LOWER the relative abundance the better as it indicates little to none of that animal in the environment monitored. In general, restoration projects ultimately aim for 5% relative abundance or lower. At this level, many forms of flora and fauna have the best chance for success.


  • Figure 1: This graph shows the relative abundance of rat chews in a variety of reserves. From the graph we can see that just under half of the reserves were free from rat chews this year. We do however also see that those reserves that have had rat chews are well past the 5% desired relative abundance. We can use these figures to pinpoint problem areas around Kaipātiki.



  • Figure 2: Here we can see the relative abundance of mice in each reserve. This shows that mice are more prevalent across the board than rats are, as they have given chews in more reserves overall. We again see, much like rats, that mice are mostly well above the desired 5% relative abundance, with only Kauri Point Domain and the Takapuna Golf Course having the 5% relative abundance this year. Despite this, don't forget the amazing reserves that have had no chews this year at all!




  • Figure 3: Here we can see the relative abundance of possum chews per reserve, this shows that possums are a rarer find than both rats and mice, as over 50% of the reserves have had no possum chews at all. The hot spots for possum activity are in Tamahere reserve, Totaravale Reserve, Smiths Bush, and Arcadia Reserve.





  • Figure 4: Finally, we see the relative abundance of the less seen "Other" species in reserves. This includes Hedgehogs, Cats, Dogs, Ferrets, Stoats and more. This year, most of the "other" bites were dog bites and show very little, other there are some wandering peanut-butter loving dogs. However, two of the locations, Glendhu Reserve and Takapuna Golf Course, had Hedgehog bites this year.





We can also look at the relative abundance of pest species across Kaipātiki by looking at all chew cards together, across all years of the campaign.

  • Figure 5: The number of cards that had absolutely no chews from any species increased this year, continuing a five year stretch of similar positive results. Looking at finer detail:

  • The number of cards with no rat chews decreased this year (bad)

  • The number of cards with no mice chews increased this year (good)

  • The number with no possum chews decreased very slightly this year (bad)

The number with no ‘other’ chews (i.e hedgehog, stoat, dog, cat) increased slightly this year (good)

Although this is showing some good results, we have to be careful as this Graph uses and collates together data from all chew cards that went out into Kaipātiki. It is better to look at specifically the lines that went out into the reserves:




  • Figure 6: Unfortunately, the number of entire monitoring lines free from any animal chews this year decreased since the previous year indicating some lines that were previously spotless, were bitten this year. It is worth mentioning that a single chew from any species ‘disqualifies’ the entire line from being free. Therefore, below are some finer details of which lines were free from particular predators:

Number of lines free from RAT chews increased significantly (by 31%) since last year. This shows some lines/areas in reserves are being very well looked after in terms of rat control. (great!)


Number of lines free from MICE chews decreased since last year, although is still higher than our baseline in 2017. This may be accounted for by the decrease in rats meaning mice survive and breed better, or their behaviour at monitoring stations is less inhibited. (bad)


Number of lines free from POSSUM chews decreased slightly from last year. (bad)


Number of lines free from ‘other’ chews (such as hedgehog, stoat, dog, cat) decreased slightly since last year. Hedgehogs and dogs were the only species indicated. (bad)



It is possible that our less than desirable results could be influenced by the Covid19 lockdowns last year, with predator control pulses affected by lockdown directly in April 2020, August 2020, February 2021 and now August 2021.



What can I do now?


Now we know what areas are most at risk and are in need of some TLC - there are four simple ways you can help our native wildlife and forests flourish instead of all these 'strangers to the NZ forest' or pest animals.


1. Join an existing restoration group, and help them check traps or bait stations. Make a big contribution or a small one - become part of a team rostered on and off when a 'Pulse' is on. Email us at enquiries@pestfreekaipatiki.org.nz and tell us which reserve you are interested in. We will link you up with that group and send you other useful information like free training opportunities.


2. Start up a new trapping group! Email us at enquiries@pestfreekaipatiki.org.nz with the reserve you are interested in and we can provide the training and equipment for you to get started. We 'pulse' four times a year so the activity is easy and effective at the same time.


3. Trap at home! We would love to see neighbours with a trap in every 1-in-3 properties across Kaipatiki. Pest Free Kaipatiki thanks to the Auckland Council has funding to assist residents trap or bait at home. You might live in an Ecological Halo and qualify for even more assistance. Email us enquiries@pestfreekaipatiki.org.nz and ask if we can help supply you with a trap. Alternatively visit our PFK Toolshed for information and to pick up a trap. It takes about 16 minutes a year to service one bait station on your property, and a bit longer to check a snap trap. All we ask in return is for you to share what you are catching or how much bait you are using - with an app called EcoTrack or by emailing us your results.

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