Invasive animals in cities

Predation from invasive mammals poses the single largest threat for the viability of native species in New Zealand, including many of our charismatic birds. To protect our unique flora and fauna, the New Zealand Government has embarked on a strategy to eradicate the most damaging introduced mammalian predators across the country by 2050. One of the greatest challenges associated with the Predator Free New Zealand initiative is to develop effective monitoring methods that help guide and assess eradication attempts, particularly within cities.

Involving the public in scientific research and using modern technologies are crucial to better understand invasive species and protect New Zealand's unique wildlife.

Victor Anton, Victoria University of Wellington

Using remote cameras

The research undertaken by Victoria University of Wellington researchers used remote cameras to estimate the abundance and distribution of invasive mammals in Wellington. Remote cameras are increasingly used worldwide to investigate the behaviour and population dynamics of an array of animals, but the use of these cameras in cities is low when compared to other ecosystems.

After setting up cameras in Wellington and comparing the data recorded by remote cameras with other more traditional wildlife monitoring methods, the researchers discovered that cameras are well suited for simultaneously monitoring multiple species of invasive mammals in New Zealand’s urban areas. One of the benefits of using these cameras is the increased number of days the devices can be active in the field without needing manual maintenance.

Getting round the camera limitations

A potential constraint on the use of remote cameras is the large number of images they may collect and the time and effort then required to classify the species present in the images. To overcome this issue, the researchers created a citizen science website where anyone could help identify the animals recorded in the photos.

Due to the potential of non-experts misclassifying various animal species, the classifications supplied by the public first needed to be compared with those provided by professional ecologists. The results of this comparison were extremely encouraging – classifications from citizen scientists agreed with those of professional ecologists up to 97.6% for some species. The researchers said this was an amazing result as it meant that the large number of photos that were collected (over 160,000) could be processed much faster and the results were still reliable.

As well as the comparison between experts and citizen scientists, the researchers evaluated several new approaches to maximise the effort of volunteers without compromising their accuracy. For example, they discovered that highlighting animal movement based on a series of three successive photographs increased the accuracy of individual citizen scientists by 7.8%. It was also discovered that weighting the citizen scientist classifications based on self-assessed confidence levels could reduce the number of volunteers required to adequately classify each photograph from three to two.

Outcomes

Using the species classifications provided by citizen scientists enabled the researchers to evaluate differences in numbers of mammalian predators between residential and forested areas.

First, they found that possums and rabbits were more abundant in forested habitats but also occurred in residential areas. To efficiently control the number of these species, the researchers suggest that urban conservation managers should target forested sites but also consider residential areas as potential sources of reinvasion.

Second, the researchers say that the large number of sites occupied by cats and hedgehogs in the study urges a review of current policies for management of free-ranging cat populations and hedgehogs, as both species can pose a major threat to endemic species in New Zealand.

Third, a common approach to prevent invasive species from reaching high densities is to concentrate management efforts on specific times of the year, but based on the numbers of invasive species recorded in urban environments, the researchers suggest that management control throughout the entire year may be needed in cities.

Overall, the research highlighted the:

• benefits of engaging the public in scientific research

• advantages of using remote cameras to monitor pests in urban environments

• importance of considering timing and location for controlling invasive species in New Zealand cities to ensure effective conservation management.