Hedgehogs Eating Birds' Eggs, Native Insects and Lizards

Forest and Bird, Issue 306, 1 November 2002, Page 10

Hedgehogs Eating Birds' Eggs, Native Insects and Lizards

—DEAN BAIGENT-MERCER

found the hedgehog which ».. changed my mind on a deserted road in Golden Bay. The back half of a native lizard poked out of its mouth, jiggling a bit as it was eaten. Until then, P’'d thought fondly enough of this creature introduced by British settlers, and the largest of the European hedgehogs. The first hedgehogs were introduced by acclimatisation societies — as early as 1869-70. ‘Later on, in the 1890s, settlers brought more out because the place got over-run with slugs and snails — which they’d brought here previously anyway, says Dr Bob Brockie, who in the 1970s studied the ecology of hedgehogs in New Zealand for his PhD. "This time they did quite well. ‘Soon after their introduction, people used to pick them up and take them to other places. Whole boxes of them were put on trains and guards would drop them off at stations along the way to help spread them all around the country. Hedgehogs spread first in the South Island. Some were taken to the Chatham Islands in 1906, and to the North Island in 1907Long regarded as a benevolent animal which ate garden pests, hedgehogs were spread widely through New Zealand in the 1930s and 1940s. As lately as 1996, somebody released them on Motutapu Island, in the Hauraki Gulf. Research in the 1990s, however, has shown them to be significant pests, eating birds’ eggs, native insects and lizards. Hedgehogs are most abundant in warm lowland areas. Usually the higher and further south you go, the fewer there are. Hedgehogs have made it to most environments, from sand dunes to mountains, with one record of a solitary hedgehog walking across the face of the Tasman Glacier.

‘In cold regions they have to hibernate for six months of the year. says Dr Brockie. ‘Around Wellington they hibernate for June, July and August’ Hedgehogs hibernate in natural holes in the ground, under toetoe clumps, roots of trees, sheets of corrugated iron, in dry corners under buildings, and in rabbit burrows. In the frost-free Far North, few hedgehogs hibernate. While classified as Insectivores, hedgehogs are now known to eat a much more varied diet. Historically, hedgehogs have been recorded scavenging shrimps washed up on beaches, dead possums and sheep, and even cannibalising on ‘hedgehog pizza’ road-kills. So it comes as little surprise that hedgehogs have been found to eat a variety of native animals. Most of the early studies on hedgehog diet were done around cities and farmland. From the early 1990s, a new generation of researchers began to document the impact of hedgehogs on native birds and invertebrates in a variety of ecosystems. Over five years Dr Mark Sanders and a team of researchers videoed bird nests on the braided riverbeds of the MacKenzie Basin, in South Canterbury. Thousands of film hours revealed hedgehogs venturing out into open riverbeds where they were responsible for 10.5 percent of predation of banded dotterel eggs and 28 percent of the endangered black-fronted tern. The hedgehogs ate the contents and carefully licked out the eggs. ‘Analysis of hedgehog guts showed that as well as invertebrates, hedgehogs also take lizards and chicks, says Dr Sanders. ‘In the last 10 years we’ve really changed our tune on the ecological impact of hedgehogs, says wildlife researcher, Dr John

Dowding. "What we thought were bumbling curiosities has been radically transformed, North of Auckland, in the sand dunes of Tawharanui, 400 hedgehogs were trapped over two years to protect nests of threatened New Zealand dotterel — but there was no relenting, the hedgehogs just kept coming. ‘During predator trapping to protect ground-nesting birds, the hedgehog is far and away the most abundant predator caught, says Dr Dowding. "This may have implications for more common birds such as oystercatchers and terns.’ Hedgehogs are enthusiastic reproducers. Most will have three litters each year (or four in the frost-free north) of five or six youngsters. They are known to swim and are capable of climbing a few metres up trees. Chris Berry studied hedgehog impacts within native forest at Boundary Stream ‘mainland island’, in Hawkes Bay. Here he found 5.5 hedgehogs per hectare and estimates a nightly hedgehog feed to consist of 150 grams of invertebrates. Overall,

this would mean hedgehogs would eat 825 grams of invertebrates per hectare, each night at Boundary Stream. He also discovered that hedgehogs and North Island brown kiwi have a 70-80 percent overlap in preferred foods. Predators of native kauri snails in Trounson Forest in Northland, have been studied by Natasha Code; she noted hedgehogs preying upon these uncommon snails. Since 1990 data has emerged to show that hedgehogs eat significant numbers of groundnesting birds’ eggs and a host of native invertebrates such as snails, weta and the larvae of moths. In towns and on farmland, hedgehogs seem harmless, cute and fascinating, but they are shaping up to be serious predators of native animals in bush and nature reserves. Back in Golden Bay, I returned next day to where I'd seen that young hedgehog eating a lizard. It was still there — only somewhat flatter.