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Jones et al (2013) hedgehog introduced tussock grassland New Zealand

Title: Impacts of introduced European hedgehogs on endemic skinks and weta in tussock grassland, Wildlife Research 40; 36-44.  2013

Authors: C. Jones, G. Norbury and T. Bell

Country: South Island, New Zealand

Background to study

A controlled experiment to investigate the impact of introduced European hedgehogs on two native skink species (Oligosoma spp.) and a large, flightless endemic ground weta (Hemiandrus spp.).

Method

  • Skinks and weta densities were monitored in late November 2005 and again in early March 2006 using 91 pitfall traps laid out in a grid, within six, 0.5 ha adjacent enclosures located within tall-tussock grassland dominated habitat in the South Island, New Zealand.
  • Pitfall trapping lasted for 8 consecutive days, pre and post treatment and skink captures were sexed and classified as adults if their snout-vent length (SVL) >50 mm. Each captured skink was marked using toe clips and densities were estimated using a closed capture models that accounting for time and enclosure related differences in capture probabilities.
  • Between November and March, wild captured hedgehogs were released into the different enclosures at densities of 0.06-9.10 hedgehogs per ha-1 to investigate the influence of different densities on the skink and weta densities.
  • To compensate for the potential restriction of food for hedgehogs within the enclosures, dog food equating to half the daily energetic requirements of hedgehogs were distributed evenly within each of the enclosures each week.
  • Each hedgehog released was fitted with a radio-transmitter and were relocated weekly during the study to check condition and weight loss, with any fatalities or individuals showing deterioration in condition being replaced by new individuals.
  • During weekly checks, hedgehog faeces were collected (n=58) during January and February and any prey remains identified to ascertain whether hedgehogs had predated either skink or weta during the study.

Key results

  • The mean density (per hectare) of common skinks and McCann’s skinks in November was 683 (se = 52.1 267 (se = 25.5) in November respectively which was similar to their estimated density in March after hedgehog density manipulation (common skinks = 777 +1, McCann’s skinks 287 + 29).
  • The proportional change in juvenile McCann’s skinks declined with increasing hedgehog density, as did the proportional change in ground weta’s encountered in pitfall traps.
  • There was a decreasing trend in overall abundance of both skink species with increasing hedgehog density however this effect was not significant but did explain a large amount of variation (64%) in the data once outliers were accounted for.
  • Analyses of hedgehog faeces confirmed that hedgehogs predated both skinks and wetas which occurred within 36% and 34% of droppings respectively, whilst beetle remains were in 55% of hedgehog droppings.

Key messages to landowners and managers derived from these results

  • Hedgehogs may have a negative impact on locally threatened or less abundant species of lizard (through predation of juveniles) or large endemic invertebrates in New Zealand and elsewhere. 

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