With New Zealand's predator free aspirations focused on rats, stoats and possums, hedgehogs may be a forgotten predator causing tomorrow's endangered wildlife.
The European Hedgehog was introduced into New Zealand from Great Britain starting in 1869 when the Canterbury Acclimatisation Society released a pair at Lyttelton. Introductions continued until the 1890's to remind the colonists of their British homeland and as a biological control agent to eat slugs and snails in gardens.
While hedgehogs no doubt do eat slugs and snails in gardens they also eat a lot else besides, including the eggs and young of ground nesting birds, large invertebrates such as weta and native lizards. Their impact is particularly severe in open habitats, such as riverbeds, where birds may nest in colonies and offer easy pickings for these nocturnal hunters.
Over the past 150 years hedgehogs have been actively translocated and have naturally spread throughout New Zealand and now occur in urban, rural and wilderness habitats below the snow line, except for the wettest parts of Fiordland. They were released in the North Island in the early 1900's and were also introduced to Rakiura Stewart Island and the Chatham Islands.
Hedgehogs can breed twice per year and they have between four and seven young at each breeding attempt so their potential rate of increase is very high. In cool and cold parts of the country hedgehogs hibernate during winter but they may remain active all year in warmer areas. They probably reached their maximum abundance during the 1950's when estimates suggested they were 50 times more numerous than in Britain.
Hedgehog density can vary from as low as two individuals per hectare up to eight per hectare. They are predated by wild pigs, dogs, mustelids (stoats and ferrets) and probably feral cats. Harrier hawks are commonly seen scavenging road killed hedgehogs.
Many people's views of hedgehogs link back to their childhood and memories of Beatrix Potter's famous illustrated children's book, "The Tale of Mrs. Tiggy-Winkle". This is the story of a hedgehog washerwoman from the Lake District who did the laundry for neighbourhood animals.
This benign, anthropomorphic view of hedgehogs may be appropriate in Britain, where the species is a native animal and under some conservation pressure. However, this characterisation is misplaced in New Zealand where hedgehogs are an invasive predator that are having demonstrable impacts on native wildlife.
Despite this, hedgehogs may be the forgotten predator as they do not feature as part of the objectives of Predator Free New Zealand. While not as high profile as rats, stoats and possums, they are likely pushing today's rare species towards becoming tomorrow's endangered species so their control should be seen as a fence at the top of the cliff rather than an ambulance at the bottom. After all, an ounce of prevention is said to be worth a pound of cure.
What's in a Name?
The familiar saying "A bird in the hand is worth two in the bush" warns about the risks that come with trying to achieve more by challenging the status quo.