I am lucky that my parents live right down the road from the Brook Waimārama Sanctuary. This 690 hectare fenced sanctuary is home to many native species and is about to be home to 40 spotted kiwis (Exciting!!!!). Within this Sanctuary there are “wētā hotels” that offers a haven for wētā, although I have also seen a giant leopard slug in there as well. I often visit the Sanctuary, it has a lot of history and diversity. Sanctuaries offer a safe space for vulnerable native species away from large predators. The surrounding predator-proof fence keeps the bad things out and the good things in. Unfortunately, the rest of New Zealand isn’t exactly pest free, with a lot of our native species being hunted down every day by introduced pests.
Predator Free 2050 is an exciting goal that is only 25 years away. With our unique flora and fauna, why wouldn’t we want our beautiful country to be predator free? Predator Free 2050 has a focus on removing several pest species (rats, mustelids and possums). Pest Free Banks Peninsula (PFBP) is a local project focused on protecting our beautiful coast, islands and land within Banks Peninsula. PFBP has several methods and tools to eradicate and monitor pests. A common toxin used by PFBP is brodifacoum.
There are concerns about whether toxins, specifically brodifacoum, is killing our native species. These tasty but deadly treats are targeted at mammalian pests, but native invertebrates have also been munching away at the cereal baits that contain the toxin when they come across it. Brodifacoum-laced baits became a popular pest control toxin in the 1990s.
Quail Island is an island found near Lyttelton. The original vegetation was believed to be a broadleaf-podocarp forest, a rare forest type seen only in small areas around New Zealand. Since 1998 volunteers have been working at restoring the native ecology of the island by regularly planting native trees and targeting pests with toxins. Evidence of native birds breeding would be a good indication that restoration efforts are working and that pest control can make Quail Island a place where native species can flourish.
Brodifacoum bait has been used on Quail Island. It is highly effective at reducing mammalian pests. Its purpose on Quail Island was to stop reintroduction of rodents. Due to Quail Island being close to the mainland, mammalian pest are able to cross over at low tide. This slow invasion prevents Quail Island from being completely predator free.
On Quail Island the brodifacoum baits were found to have been nibbled by wētā and other invertebrates! This discovery flustered scientists. How many other native invertebrates have yet to be identified for consuming the bait?
This discovery led to increasing concern for our wētā species, many endangered or threatened. How many have died due to our toxic baits?
Studies focused on invertebrate consumption of baits have primarily used baits containing 1080. The studies that involve brodifacoum have also only focused on short-term effects (14-21 days) and one-off consumption of the bait. These hungry invertebrates are likely going for more than one course of their bait snack.
Mike Bowie and James Ross wanted to determine whether wētā were regularly consuming these forbidden snacks and whether they would survive when they did. They tested in the field and did a laboratory experiment too. The laboratory experiment consisted of wētā being fed either baits with or without brodifacoum and then monitored for 60 days for insect mortality. The field test involved monitoring traps around Quail Island for invertebrate activity.
Unfortunately, the wētā were hungry. For the field test they found that wētā and invertebrates would line up and wait their turn to eat! The wētā had distinct bite patterns when eating the bait, compared to pests such as mice. Wētā bite marks were easy to identify. In the laboratory test there was no significant difference in mortality of wētā (50% survived that were fed bait, 71% survived that were fed the control ). Mike and James determined more research was needed to be done in order for results to be more conclusive.
So, what does that tell us exactly? The baiting methods we use to get rid of the bad things are also attracting the good things! Our native species are eating the toxins we are using to remove the pests that are eating our native species! We need to find a compromise, a less risky option for our often overlooked native invertebrates.
Brodifacoum is also a risk to birds’ species! If a bird eats an invertebrate that has eaten brodifacoum, they will be affected by the poison as well. Joanne Hoare and Kelly Hare agree with this and suggest using non-toxic or less toxic methods for pests to protect native species. There seems to be a common theme with studies done on brodifacoum… its toxic for every species! There are several concerns, not just about birds and wētā consuming the bait but many other invertebrates and species consuming it as well.
So, to bait or not to bait? Mike Bowie and James Ross showed that although there were no significant differences in mortality through the laboratory test, the wētā were eating the bait in the field test and laboratory test. I believe that in order to protect our native species, a less toxic baiting method should be considered. This will reduce long-term harm to species such as wētā. All though brodifacoum is highly successful at getting rid of pests, it can also harm other species. If there are other methods that reduce that risk, we should start with those methods then move to toxic baits as a last resort option on ecologically sensitive areas, such as Quail Island.
The author, Kayla Valentine, is a postgraduate student in the Postgraduate Diploma of Science at Te Whare Wānaka o Aoraki Lincoln University. This article was written as an assessment for ECOL 608 Research Methods in Ecology.
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