Hedgehogs pose one of the greatest threats to our unique and threatened ecosystems.
Description
The hedgehog is an unmistakable, small nocturnal mammal. It is grey-brown in colour with its back and sides entirely covered with spines.
Hedgehogs are mainly insectivorous, however they will eat almost any animal substance and some plant material. They find much of their prey by smell.
Hedgehogs are widespread in Aotearoa, occupying grassland, braided riverbeds and drier forest habitat.
Hedgehog densities are highest in farmland, lower in river braids and lowest at high altitudes and in high rainfall forest. Even at relatively low densities of six individuals per km2 on river braids, they can cause significant losses to ground-nesting bird colonies.
Hedgehogs are mountain climbers and have been recorded roaming the hills up to 2,000 metres above sea level.
They are able but reluctant swimmers, and the same can be said for their fence climbing and rock hopping abilities.
The threat
Our most underrated predator
One hedgehog can cause an entire colony of endangered black-fronted terns to abandon their nests.
Analysis of hedgehog gut contents and a growing catalogue of camera footage tell a compelling story. Hedgehogs hoover up countless endemic birds’ eggs and chicks, lizards, and invertebrates.
In braided river systems they feast on the eggs and chicks of banded dotterels, black-fronted terns and pied oyster catchers. Our critically endangered kakī (black stilt) struggles to survive in the wild due to hedgehogs and other predators plaguing their habitat.
Hedgehogs have a voracious appetite for invertebrates and take many local endemic species. They are known to eat the rare giant native centipede, wētā and other rare insects.
They eat the native snail Wainuia urnula. Lowland populations of Powelliphanta snails may also be severely affected, particularly the Patarau and Otaki sub-species. Only smaller (juvenile) snails are eaten, but this severely affects recruitment and population recovery.
Hedgehogs also prey upon lizards, particularly in cooler periods when lizard activity slows. Skinks are particularly at risk. Beetles are a key prey in many studies. In suburban areas and on farmland they eat beetle larvae and earthworms.
It is possible that hedgehogs also prey on endemic frog species, as they are known to take introduced frogs and their range overlaps with some New Zealand frog species.
In forests and drylands, they eat native grasshoppers and wētā, lizards, frogs, eggs, and chicks of ground-nesting birds and scavenge on carrion (dead animals).
Pests, not pets
Despite the clear evidence of the harm they do to our natural environment, many people still believe hedgehogs do not fit into the same category as stoats, possums, rats and feral cats.
As with our other predator species, the choice is between our native taonga and endemic species or introduced pests.
Hedgehogs cannot coexist with our endangered species. Removing them from the environment is an essential step to saving what makes Aotearoa unique.
Why we can't ship them ‘home’
Hedgehogs are listed as ‘Least Concern’ on the IUCN Red List, whereas many of the species they prey on in Aotearoa are endangered or even critically endangered.
In Europe, their total population totals around 500,000 individuals. Habitat loss poses the greatest threat to hedgehogs in Europe, followed by predation and road kills, so bolstering their population with individuals from Aotearoa would not solve the underlying issues surrounding their decline.
Although transporting hedgehogs’ ‘back home’ is not an option, studying their behaviour and movements in Aotearoa can help with hedgehogs’ conservation efforts overseas. Conservationists in Aotearoa are sharing knowledge with conservation groups in Europe to help protect hedgehogs where they are native.
DOC's work
DOC has known of the impact of hedgehogs for some years, with time-lapse video footage providing evidence of their direct predation on ground-nesting birds in braided river systems.
As a result, many ground-set trapping programmes will have hedgehogs as part of their catch. These include programmes in open country like Central Otago, braided river systems in South Canterbury or forest ecosystems all over the North Island.
In the long-term, hedgehogs will need to be removed entirely from our environment, much like stoats, possums and rats.
With knowledge of barriers to hedgehog movement, we can focus landscape control on areas of high conservation priority that are bordered by features that slow reinvasion. Borders include mountain ranges above 2,000 m, existing rabbit fences, and rivers and lakes.
A landscape-scale tool for controlling hedgehogs is currently being researched and developed. Traps need to be at such a high density that they are not feasible, and current toxins are not manufactured to target hedgehogs.
On a smaller scale, dogs, thermal imaging, spotlighting and intensive trapping are all effective tools for finding and removing hedgehogs from the environment.
You can help
You can control hedgehogs in your area.
Signs hedgehogs are present
Prints are five-toed, resembling a large rat print. Forefeet are much broader and shorter in length than the hind feet, meaning there are two distinctly different prints left by the one animal.
Droppings are black (with a dark greenish colour to fresh droppings), 30-50 mm long and 7-10 mm wide. They are usually dryish, and usually contain tightly packed recognisable fragments of invertebrate exoskeletons (for example beetle carapaces, head or body segments).
Movement and snuffling can often be heard before a hedgehog is sighted.
Control methods
Traps
DOC250, 200, and 150 traps are all capable of humanely killing hedgehogs. Bait selection and trap aperture size are important, as well as trap placement and timing.
The entrance to the trap should be 80 mm x 80 mm to allow the largest hedgehogs to squeeze through. In areas with pets this is the ideal size opening to prevent anything larger (like cats or dogs) getting in.
Goodnature A24 traps are effective backyard traps that can kill hedgehogs. They are self-resetting and only require a dollop of bait such as peanut butter in the top. Follow the manufacturer’s instructions for safe handling and installation.
Some backyard traps such as Victor rat traps may catch and kill hedgehogs but are not recommended for anything larger than a rat. If you find a hedgehog alive in your trap, it must be euthanised humanely.
Baits
Where you live and what hedgehogs eat in your area will determine what bait they are most likely to go for. They can have expensive tastes, preferring salmon above most things, but will also go for rabbit meat, eggs, mayonnaise, peanut butter, dairy, or anything fatty.
It is worth changing bait types by adding an additional bait to the trap before removing another bait type. For example, if you want to test eggs as a bait but you have been using rabbit meat, add an egg with fresh rabbit meat before phasing out rabbit meat completely. This means the new bait won’t be completely unfamiliar to sceptical individuals.
Where and when to trap
Hedgehogs like to travel along fence lines, buildings and anything obstructing their path. When trapping, this can be used to your advantage.
Place traps along these features so hedgehogs naturally choose to walk into the entrance. ‘Run-through’ style traps are good for this, where hedgehogs can see an exit point on the other side of the trap. Making the trap plate level with the floor of the trap will also encourage hedgehogs to enter.
In the North Island hedgehogs can be trapped all year round. In colder southern regions they hibernate from mid-April to mid-September.
It is best to open traps at the same time as hedgehogs wake from hibernation. They will be hungry and more likely to enter a trap at this time. It is also important to start trapping them before ground-nesting birds lay their eggs.