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Doncaster (1994) hedgehog factors affecting local abundance

Title: Factors regulating local variations in abundance: field tests on hedgehogs, Erinaceus europaeus, Oikos 69(2); 182-192. 1994

Authors: C. P. Doncaster

Country: UK

Background to study

An investigation using the augmentation of hedgehog populations to determine how dispersal, mortality and natality is influenced by density.

Method

  • Hedgehog populations were monitored for 6 months at three Oxfordshire sites; two within agricultural land with high and medium badger density and one within amenity grassland with low badger density.
  • Within each site, hedgehogs were located using spotlight surveys and 5 of 10 (low density), 26 of 26 (control) and 38 of 50 (high density) hedgehogs at the three sites were fitted with radio-transmitters. 24 of 26 hedgehogs from the control site were removed and added to the low density population (artificial increase) and were replenished at the control from 24 of the 38 hedgehogs in the high density population (artificial decrease).
  • Fieldwork which involved tracking individuals to obtain at least 1 fix per week per individual was carried out during summer 1992 for 1 month before and 3 months after each augmentation.
  • Hedgehogs not radio-tagged (n=54) were uniquely marked using a microchip transponder.
  • Known fates of radio-tagged individuals were recorded and survival and causes of death compared between the expanded and reduced populations.
  • Dispersal of individuals was measured using location data obtained from radio-tagged individuals and habitat preferences were quantified for preferential use or avoidance with respect to habitats available.
  • Comparisons between growth rates were calculated from rates of change in body weights of males.

Key results

  • A rapid response to manipulations of population size was observed suggesting density dependent regulation in hedgehog populations:
    • Artificially reduced population occupying amenity grassland showed a reduced rate of losses compared to before the density manipulation, and a rapid recruitment of adults (44 new hedgehogs after three months) contributing a 50% increase in the first month.
    • Artificially increased population on agricultural land with high badger density reduced by 65% in the first month with the majority of losses resulting from death (mostly predation by badgers) and emigration (>100 m from release site) and had only 9 new recruits recorded during the study period.
  • The control site was likely to be at carrying capacity in terms of food resources as the population exhibited a low immigration rate, individuals transplanted into the control site exhibited a lower weight gain compared to those transplanted into the increased population and individuals that dispersed from the control showed the best growth rates.
  • The artificially increased population dispersed further than the control and centred their activities around the vicinity of rural houses suggesting they responded to the increased predation risk at this site.
  • Males added to the low density population exhibited an increased growth rate.
  • Predation by domestic dogs was high at the amenity grassland reduced population.
  • Across all three sites, arable land was visited proportionally less frequently than its availability.
  • Woodland habitats in the control site were under-utilised and pasture was the preferred habitat in the agricultural artificially increased population and in the amenity grassland artificially reduced population.

Key messages to landowners and managers derived from these results

  • Badger presence is a major limitation to hedgehog density, particularly in agricultural landscapes where the two species can co-exist. Suitable habitat around rural dwellings may help to provide refuge for hedgehogs from badgers and thus help their persistence within an area and maintain a metapopulation system.
  • Urban habitat, in particular amenity grassland and surrounding pasture are favourable habitat for hedgehogs where their densities are highest. These areas should be maintained/created alongside suitable hibernacula areas including hedgerows

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