Hedgehogs were first brought to New Zealand by acclimatisation societies to remind settlers of their homeland, but were later introduced in greater numbers to control garden pests such as slugs, snails and grass grubs.
Today, hedgehogs are abundant throughout New Zealand, and pose a significant threat to many of our native species.
In many areas of New Zealand, there are now estimated to be between 2 and 4 hedgehogs per hectare (and in some areas as many as 8!)
The hedgehog is an unmistakable small nocturnal mammal, grey-brown in colour with its back and sides entirely covered with spines. They are 150-250 mm in overall body length and reach a maximum of around 1 kg, but their weight can drop dramatically during winter hibernation.
Though males tend to be slightly larger than females the difference in size and weight is not obvious.
Hedgehogs rely on their spines for protection and roll into a tight ball when threatened.
In winter, hedgehogs hibernate. Winter dens are under tree roots or deep dry litter, in rabbit burrows or other dry refuges. Male hedgehogs begin hibernation much earlier than females.
Then in spring, as early as September, the long breeding season starts, yet young may be born as late as May. Two litters can be produced per year, each of 4-7 young; however juvenile mortality is high. The young are independent after about 7 weeks.
Hedgehogs’ preferred habitat is lowland pastoral areas, and they become less common with increasing altitude. Although previously thought to be mostly absent from extensive forest, recent studies show they are regularly trapped within large forest tracts (for example in Trounson and Rotoiti), and are found above the bush line in extensive forest areas such as the Kawekas. Home ranges are not defended and can overlap with many others. Hedgehogs will usually have several daytime nests, which are sometimes used by other hedgehogs when not occupied.
Hedgehogs are mainly insectivorous, with key prey items being slugs, snails and larger insects, but will eat almost any animal substance and some plant material. They find much of their prey by smell.
The extent to which hedgehogs impact upon the New Zealand environment is only recently beginning to be understood in any detail. Here is a summary of findings:
Hedgehogs are proven to be a major predator on eggs of riverbed breeding birds such as banded dotterel and black-fronted tern, and have been known to kill and eat chicks of a variety of ground-nesting birds.
In the MacKenzie Basin (South Island), hedgehogs have been found to be responsible for one in five predator attacks on nests.
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 have been known to 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.
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.
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 in open country like Central Otago; braided river systems in South Canterbury; or forest ecosystems all over the North Island; will have hedgehogs as part of their catch. This will help protect animals as diverse as kaki/black stilt, Cromwell chafer beetle, Grand skin, black-fronted tern and weta.
You can help stop hedgehogs
Don't encourage them into your backyard by creating burrows for them or leaving milk out.
Set a suitable trap for the situation you are in (suburban or rural).
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.
DOC uses the DOC150, DOC200 and DOC250 which are powerful and effective kill traps.
To be safely set, however, traps need to be placed inside a tunnel-like trap-box to ensure that birds, children or pets cannot get access to it. The box also orients the hedgehog in the right direction to be caught in the trap, disguises the trap, and protects it from the weather.
A simple wooden tunnel can easily be built at home.
The tunnel should be placed along a natural runway so that approaching animals must either pass over the trap or turn back. Suitable sites are along fences, hedges or the banks of a stream, in bush among tree roots, beside fallen logs or in dry culverts. The entrance must be cleared of leaves and weeds.
It is preferable to bait traps, though a well-placed trap can still catch hedgehogs without bait. Fishy cat food or freshly killed rabbit or chicken is excellent but does not keep well. A longer-lasting alternative is an egg which can be left whole or broken. Alternatively two eggs can be used. Make a small hole in one egg to provide a scent and leave the second egg whole to provide a long-lasting visual lure.
Setting the trap can be a little tricky, so make sure you follow the manufacturer's instructions and take care with fingers.
It is recommended that you lay traps for hedgehogs at the beginning of the birds’ breeding season, when hedgehogs may be at their most damaging, and in the autumn, when adult females can be targeted. Male hedgehogs begin hibernation much earlier than females, who delay hibernation to build up food reserves after the breeding season.