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Hedgehogs pose prickly problem for native fauna

Hedgehogs pose prickly problem for native fauna

Studies by Landcare Research suggest that hedgehogs are responsible for significant levels of predation on skinks and ground-nesting native birds' eggs, and raise suspicions that mature females may be the worst culprits. The work is also building a clearer picture of the extent to which hedgehogs prey on rare native invertebrates.

The hedgehog - friend or foe? Landcare Research scientists have been tracking hedgehogs using spools of thread and radio transmitters, to investigate how they forage. Diet studies have shown that some native birds, skinks and invertebrates are at risk.

Hedgehogs are regarded with benign indifference by most New Zealanders, who tend to see them as appealing creatures that eat garden and pasture pests. Hedgehogs were introduced in the late 19th century and are now widespread, and estimated to number between two and four per hectare in most areas, perhaps reaching as many as 8 per hectare in optimum conditions.

The hedgehog's diet consists mainly of invertebrates, but there is plenty of evidence from their native Europe that they eat other foods, including eggs and chicks of ground-nesting birds. Department of Conservation video monitoring from 1994-99 revealed that hedgehogs were responsible for about 20% of all recorded predation of banded dotterel and black-fronted tern nests in a braided riverbed system in the Mackenzie Basin.

Landcare Research scientist Dr Chris Jones has been investigating hedgehog foraging behaviour in the same area, with particular focus on whether all hedgehogs forage on birds' eggs to the same degree, or whether 'rogue' individuals cause more damage. He attached spools of thread to a sample of radio-tagged hedgehogs and followed the foraging paths revealed by the thread.

"Our initial results show that of ten hedgehogs studied in detail, only one female habitually used the river bed where the birds nest, while the others almost never did."

In upcoming research, Dr Jones will spike chicken eggs with chemical markers and set them on the riverbed, to reveal which individual hedgehogs have a taste for eggs. The culprits will be identified through telltale markings in hairs and whiskers, which show up under ultra-violet light. Repeat offenders will have multiple markings.

Skinks and insects in peril

Along with colleagues from DoC, Dr Jones has also been studying the diet of hedgehogs to determine how frequently they prey on rare native skinks. Skink remains were frequently found in the guts of trapped hedgehogs and around one in every eight hedgehog droppings from Central Otago contained lizard remains. Adult females appeared to be the main culprits. An analysis of gut contents from 615 hedgehogs trapped in the Mackenzie basin showed that native lizard remains (mainly skinks) were present in three times as many adult female guts as adult males. An even more pronounced difference was found in a smaller scale DoC study from Macraes Flat, Otago.

"This level of predation is obviously a threat to skinks, some of which are rare, and most of which already face decreasing habitat and predation from other introduced pests such as stoats and feral cats," Dr Jones says. "The threat to native invertebrates should also be considered * after all, hedgehogs are primarily insectivores.

"In the Mackenzie basin, hedgehog guts were found to contain rare endemic native beetles and weta, with one gut containing 283 weta legs! In Central Otago, hedgehogs consume rare chafer beetles.

Hedgehogs also eat native grasshoppers, many of which are rare and only occur in very limited areas." The threat of the unknown Dr Jones says although current studies are helping to build a clearer picture of their impacts, hedgehogs remain under-researched.

"Stoats, ferrets and possums get all the attention. They are like the bad guys in balaclavas during a bank heist. Meanwhile, hedgehogs are the guys in the background, quietly opening the safe. "Hedgehogs pose a consistent background threat. My goal is to find out more about what that threat entails.

"It may be that whilst all hedgehogs pose a threat, mature females may know how to get the best access to quick and easy sources of high energy, such as eggs and lizards, which are especially important during the breeding season."

Dr Jones says because of this, he would recommend that land owners and conservation managers 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 females can be specifically targeted.

"Males go into hibernation much earlier than females, who must race to build up food reserves after a taxing breeding season and before hibernation."

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