Kia ora koutou
Welcome to the latest edition of Kararehe Kino, which is a little different from its predecessors. Firstly, we have made a subtle change to its sub-title: from ‘Vertebrate Pest Research’ to ‘Animal Pest Research’. This is to reflect the wider scope and context of our contemporary research, which includes work on wasps and other invasive invertebrates and their impacts. Secondly, for the first time in a while, this is an issue without a theme. We felt there were a number of interesting research stories that might not fit into a themed issue but that were really worth sharing with our stakeholders and end-users.
Finally, and on a more personal note, this is my first editorial as leader of the Managing Invasives portfolio within Manaaki Whenua – Landcare Research after stepping into the role following Dan Tompkins’s shift to manage the science strategy for Predator Free 2050. I’d like to acknowledge the great job that Dan did in managing the portfolio and in providing oversight to Karerehe Kino over the past few years. We also managed to squeeze one more article out of Dan before he left. In it Dan describes how PF2050 came about, what it’s trying to achieve, and how this will be rolled out. It is a timely and valuable overview that provides a perspective on much of our work.
Dan’s overview of PF2050 ends with a reference to our national need to control pests in order to protect our imperilled native biodiversity. This is a point that Rachelle Binny and her colleagues expand on in their article describing their attempts to use outcome monitoring data from multiple conservation sites across New Zealand to identify and quantify the benefits of pest control. One of the most challenging aspects of the work for the team was the fact that the sites collect data on different things in many different ways. The researchers highlight the need for some consistency in how biodiversity outcomes are monitored, particularly in the light of the renewed national efforts to control mammalian predators, so that the massive expenditure on programmes can be justified and realistic expectations set.
Rachelle and her colleagues rightly point out that, despite its importance, predation is not the only thing that affects threatened populations or the habitats in which they exist. Ecology is incredibly complex, and unlike in some of the ‘harder’ physical sciences, subtle interactions between species and their environments mean that we must always be on the lookout for unexpected relationships and management effects. Some of these subtleties are explored in two of our other articles.
In one, Deb Wilson and colleagues discuss possible reasons why rat-tracking rates did not increase following possum control on the Otago Peninsula, as might have been expected from similar responses at other sites. In the other, Pablo Garcia-Diaz discusses the impacts of introduced mammals on breeding colonies of two South American seabird populations. It may surprise some people, but Pablo found that rabbits had the most significant impact on the breeding productivity of a burrow-nesting shearwater population. There are interesting parallels in this finding to our own fight against introduced mammalian pests. In the 1970s, production of grey-faced petrel chicks on Moutohorā in the Bay of Plenty was negligible due to the impacts of Norway rats. Rat numbers were sustained on the island outside of the petrel breeding season because of their predation on rabbits.
One of the reasons for enlarging the scope of Karerehe Kino from its original focus on vertebrate pests is to acknowledge the work our researchers do on other invasive animals. In his article, Dean Anderson describes how mathematical modelling helped him to identify the most cost-effective strategy for eradicating electric ants from areas of Queensland where they have become established, probably as ‘hitch-hikers’ on potted plants. Dean notes that the electric ant is considered to be one of the world’s worst invasive species due to its rapid spread from its native South American range.
The rise of new or ‘emerging’ invasive species is addressed by Darren Ward. Darren and his colleagues studied a massive global database to try to understand if patterns in the distributions of emerging invasive species can help to predict future risks. Their analyses showed that many new invaders are being detected, possibly as a result of ever-expanding global trade networks and climate change. This, warns Darren, means there are still large numbers of potential invaders that nations have yet to encounter.
Much of our core research still deals with detecting and controlling vertebrate pests. There is currently a great deal of interest in the use of trail cameras as monitoring devices that don’t require the animal being monitored to interact with them beyond moving within the camera’s field of view. Grant Morriss and Graham Nugent discuss the use of cameras to monitor the effects of deer-repellent-coated 1080 baits on sika deer numbers. They also describe using the collected images to infer changes in possum numbers following control, and also how they might provide insight into interactions between the two species. The use of trail cameras is also discussed by Al Glen and colleagues, who use them on Hawke’s Bay farmland in a study comparing their ability to detect feral cats with that of specially trained detector dogs. They describe the pros and cons of using dogs to detect pests and look at how dogs’ abilities could be used in optimal search strategies.
As well as developing new technologies, it is important to modify and improve existing techniques. In their article, Bruce Warburton and Grant Morriss test a series of modifications to leg-hold trap sets to see if possum capture rates can be increased. They describe how changes to the distribution of the standard lure and the addition of more visual cues had the desired effect. Most of the pest control that we use requires individual animals to interact with a device or a bait. Graham Nugent and his colleagues raise some fascinating questions about how learned aversion and species-specific behaviours can influence the effectiveness of control when comparing variants of the dual-1080 bait drop. Their work highlights the fact that only by understanding these details can we really understand why some baiting regimes are more effective than others and modify management based on reliable information.
Understanding and modifying predator behaviour may also be the key to reducing impacts on threatened prey species when lethal control cannot be used (e.g. where social factors limit the available methods, or overseas, where pests are native species), or has not resulted in complete eradication of the pest. Grant Norbury explains how super-saturating the environment with prey scent cues can lead to reduced predation on the prey themselves as predators learn that the scent more often than not leads to no food reward. As the last two articles show, there is still much to be learned about how pests behave, and about how that knowledge can be used to manipulate those behaviours to our advantage.
Portfolio leader - Managing Invasives