Here is an update on the Polhill Reserve from our Halo Hero, Marc

Marc Slade

Marc Slade Photo by: Tim Park

Hi Nick.

It feels like ages since I last wrote, but a heap has happened since then. I will fill you in on a few of the key events:

Volunteers social

Given the number of people who volunteered their time to the project, we decided to hold a social gathering as a way of saying thanks and keeping people updated about what was going on. The hui was a great way of helping people get to know each other and, in the event, provide training on the coming chew card monitoring (see below). We hired Aro Valley Community Centre (kindly donated by Lisa & Geoff Whittle), laid on some baking and invited people to “bring a plate”, fish and chips and a bottle of beer. We had guests; Geoff Simmons from the Morgan Foundation who inspired us by talking about the “Halo Project” and future plans to make Wellington City Predator Free by extending predator control, and Matt Robertson, WCC Park Ranger, who gave an informative briefing on the chew cards. The evening was well attended – thanks to those of you who came. We will aim to hold another get together in the autumn.

Citizen science – In action!

As mentioned in my last entry, a big event last year was carrying out a monitoring exercise to detect the presence or absence of the key predators, and give us some clues around numbers and where they are hanging out. We embarked on this partly because of relatively low trapping numbers, hopefully a good sign showing low numbers of the “big three” – rats, possums and mustelids (stoats & weasels), but potentially showing that the current regime isn’t working as well as it could and needs tweaking. We opted to use “chew cards” (a topic well covered on the Halo website). Chew cards are a relatively simple and inexpensive tool to allow community groups and landowners to detect the presence of pests.

We laid out 120 “cards” (chew cards are small “core flute” cards filled with peanut butter bait, folded in half and nailed to a tree – apparently animals find them irresistible) along all the existing bait lines at 50-meter spacings. Given the bait lines run west to east across the reserve in straight lines irrespective of topography, this was a challenging exercise. We had to put all the chew cards out on the same day, leave them 7 nights and then retrieve them – again on the same day. This was a logistical feat as volunteers needed to measure 50m between cards using lengths of rope, fix the cards to trees, mark the location with a length of orange ribbon and record the card number sequentially all whilst traversing the steep and slippery terrain. Luckily we had a stalwart band of volunteers who carried out this exercise highly efficiently and with barely a grumble.

A bonus was that our project featured on Radio New Zealand’s “Our Changing World” in an item about the Halo effect around ecosanctuaries such as Zealandia. Our feature was followed by Nick talking about the wider project.

The hills are alive – with the patter of tiny feet!

The monitoring exercise proved really useful, as not only was it good for team morale (and enjoyable for those who enjoy sliding down muddy banks on their backsides – luckily a good number of our volunteers!) but it showed us that there are still relatively high numbers of predators in the reserve, despite current trapping and baiting efforts. One of the biggest surprises was the relative abundance of possum chew marks – something we hadn’t suspected given the council’s long running baiting operations using toxins. We also detected weasels, rats-a-plenty, hedgehogs and the ubiquitous mice.

Chew card

Chew card Photo by: Tim Park

A change of tack?

The results of the monitoring help to show us what is actually living in the reserve, its rough distribution and approximate numbers. Using this information we can adjust the way we trap, the type of bait we use and where we place our traps. An example to illustrate this is that despite the regional council targeting possums by putting kilogrammes of the poison Brodifacoum into the reserve’s bait stations every three months we detected relatively high levels of possum “chew” on the cards. There could be a number of reasons for this, but it raises the question – is the current baiting regime actually effective in getting possum numbers low enough to allow the bush and its “manu” (birds) to recover? We will be taking this question to the council and looking at alternatives, including putting in possum traps to supplement the bait stations, and potentially reducing the frequency of using the toxin in the reserve – surely a good thing in terms of the overall “mauri ora” of the place (ecological health). In relation to the other predators detected we may try switching bait or adding additional traps.


Bomarea Photo by: Tim Park

Day of the Triffids – the importance of weeds

While we were recovering the chew cards we noticed a profusion of attractive orange flowers throughout the reserve. Attractive as they are we recognised these as belonging to the highly invasive climber – Bomarea (Bomarea multiflora). Bomarea comes from South America and is becoming an increasingly problematic weed in New Zealand. The Council has previously carried out control of this weed in Polhill, and thought they had got on top of it. The fact that volunteers reported heavy infestations of it in thick bush on both sides of the reserve highlighted, however, that this is not the case.

This discovery is significant as plant pests can be every bit as damaging to native ecosystems as animal pests. Plants such as bomarea, old man’s beard, banana passion fruit and many others can smother forest trees leading to canopy collapse and preventing native seedlings from re-establishing. Controlling weeds is as important as trapping predators in a restoration project such as ours. We reported the sightings to the council and we will now carry out weed “surveillance”– passing on observations to Illona – the Council’s pest management officer.

Anenome stinkhorn Photo by: Tim Park

Anenome stinkhorn Photo by: Tim Park

On a more positive note some of the teams spotted interesting “biodiversity” whilst they laid out the chew cards, including a number of birds; saddleback, kereru, robins, pipiwhareoa (shining cuckoo) but also some fascinating fungus – the bazaar looking anemone stinkhorn.

Kaka nest

In my last blog I reported that we had found a kaka nest in an old pine stump at the edge of the reserve. A number of us monitored the nest daily and WCC installed a “trailcam” to give footage of the comings and goings of the pair of kaka. Matu Booth (Zealandia) and Matt Robertson (WCC) also used a mirror to spot how the nest was doing. After 20 or so days it became apparent that only one out of the five eggs had hatched. From day 1 we had been concerned about the risk to the eggs or the chicks from predators – rats, stoats or cats. We even installed a DOC200 trap in a property close to the nest site. We were all highly excited when we heard that one of the eggs had hatched and at least one chick might make it to swell the number of kaka screeching around Wellington. Unfortunately after a particularly wet week and a windy night Matt discovered that the tree in which the nest was located had collapsed, killing the chick! When he arrived that morning he reported the kaka mother hanging around near the nest looking highly forlorn. Who says animals don’t have feelings?

Sad though this is, it shows that in nature animals tread a thin line between life and death, even without invasive predators. An interesting “afterward” is that three of the unhatched eggs were recovered and an “autopsy” was carried out. It was discovered that the eggs had failed at various stages and some of the embryo had developed with no eyes. Could this be a result of inbreeding caused by the low numbers of surviving birds?

Battle for the birds – The trapping continues

DOC has been in the news recently for increasing its predator control in response to a particularly heavy beech mast this year. This has been dubbed “The Battle for the Birds”. This is a great initiative, but still only covers less than 10% of New Zealand. Meanwhile community groups across Aotearoa continue to control predators on private and council owned land.

As well as the all the other stuff we have been doing its important to report that the volunteer teams are still regularly checking the traps – and we caught quite a few rats and hedgehogs over the holidays. Last week a weasel was seen running across Ashton Fitchett Drive into the bush. This just shows that the predators are still out there and that we need to keep up the effort to restore the dawn chorus in our backyards.

What now?

We will continue trapping but we are also planning to carry out banding and nest monitoring of the NZ robins and saddlebacks in the reserve to see if they are successfully rearing young. We will also begin to develop a restoration plan, seeking to reintroduce some of the missing forest trees and shrubs that would have once graced these slopes – species like tawa, kohekohe, nikau and rimu.

I’ll keep you updated on how we are doing.

Marc  Slade