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Campbell (1973) hedgehog feeding behaviour New Zealand

Title: The feeding behaviour of the hedgehog (Erinaceus europaeus L.) in pasture land in New Zealand,  Proceedings of the New Zealand Ecological Society 20; 35-40. 1973

Authors: P.A. Campbell

Country: New Zealand

Background to study

A study investigating the size, distribution, dispersal behaviour and feeding ecology of a natural population of hedgehogs occupying pasture land habitat in New Zealand and their impact as predators of pasture pests. 

Method

  • Hedgehogs were captured, marked and recaptured over 2 ½ yrs using spotlight surveys of two four hectare blocks of white clover and ryegrass dominated short grazed and winter irrigated pasture land.
  • Survey blocks were separated into 20 x 20 m grids and the location of each marked individual plotted to calculate minimum summer feeding ranges derived from minimum convex polygons.
  • Hedgehog density/hectare was calculated by season and year using a stochastic capture-recapture model.
  • Prey availability was measured using 12 pitfall traps checked for overnight and weekly captures and by sweep netting once per week, both for one year. In addition, 100 randomly located soil core samples (10 cm depth) were taken every two months to measure presence of grass grub and porina larvae. 
  • Prey eaten by hedgehogs was calculated by assessing the relative frequency of occurrence, scale of abundance and direct counts of prey items identified in stomach contents of 60 individuals captured in pasture habitat and in faecal samples collected from survey grids.
  • The error relating to prey identification from faecal samples was calculated using a controlled experiment of one individual in captivity whose faecal samples were assessed for the presence of 12 major prey items that were made available and in which the quantities of each were known to of been eaten.
  • The role of hedgehogs as pest predators was assessed using the potential daily consumption of grubs per hedgehog per day (detailed in East, 1972) and accounting for density in the study area.

Key results

  • Population size ranged from 30 in the winter when hedgehog mortality was the highest to 64 in March 1971 which equates to a density of between <4 to 8 hedgehogs per hectare.
  • At least 20 hedgehogs over the study period were presumed residents (recaptured 10 – 46 times) and an increase in transient males in the study area was associated with the breeding season.
  • At least six individuals remained in the study area for the entire study period and thus were >3 years old.
  • Mean minimum summer feeding ranges for adult males and females were 2.4 and 2.8 ha respectively and for juvenile males and females were 1.9 and 2.0 ha respectively. The largest range was 4.6 ha and females had slightly larger feeding ranges than males except during breeding when males extended their ranges.
  • 101 potential prey species were identified from pitfalls and sweep netting. No grass grubs or porina larvae were identified in the study area.
  • Major prey items included lepidopteran larvae, earwigs, unidentified beetles, spiders, harvestmen, grass grub beetles, slugs and earthworms and during the flying season of grass grub beetles and porina moths, these species were almost exclusively eaten by hedgehogs.
  • The relative contribution of grass grub beetles and porina moths is underestimated when using faecal samples alone to identify prey items of hedgehogs.
  • At a density of eight per hectare, hedgehogs have the potential to destroy between 10 and 40% of the adult population of grass grub pests during the flying season and have the potential to also exert some pressure on porina moth pest species.

Key messages to landowners and managers derived from these results

  • Surveys estimating hedgehog density must account for transients particularly during the breeding season, thus replicated surveys across seasons is recommended to accurate estimates of density.
  • Dietry analyses using faecal sampling methods need to account for error in detecting species and controlled manipulation of prey and the subsequent recovery of prey items in faeces is useful for identifying error and suitable correction factors.
  • Management that may temporarily reduce the suitability of hedgehog habitat should not be carried out during the breeding season when females reduce their ranges for rearing young.

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