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Cassini and Krebs (1994) hedgehog behavioural responses food

Title: Behavioural responses to food addition by hedghogs, Ecography 17; 89-296. 1994

Authors: M.H. Cassini & J.R. Krebs

Country: UK

Background to study

Food availability is expected to be a crucial factor regulating the size of populations and patterns of space use by individuals.  This study is an investigation into the influence of food availability and social oragnisation on the pattern of distribution and abundance of hedgehogs at a local scale.

Method

  • Two part study on sports ground habitat in Oxford which consisted of a) a ten night observational study using visual scans, to determine the location of hedgehogs/30 minute intervals during May 1992 and b) a 24 session experimental study determining the location of marked hedgehogs in relation to supplemented food between 18th July and 13th August 1992.
  • 24 adult hedghogs (15 males, 9 females) were marked for the experimental study using uniquely coloured betalights fitted to tubes fixed to the spines of each animal.
  • Experimental study involved placing 34 food supplements (c. 4g cat food), each placed on circular plastic sheets within one of four sectors of the study site (NW,NE,SE and SW). Experimental phases included a) no food supplemented for 6 days b) food supplemented in a 10x10m grid marked by flags in NW sector for 7 days; c) no food supplemented for 6 days; d) food supplemented in random locations and not marked in NE sector and e) no food supplemented lasting 3 days.  A flag test to determine whether hedgehogs associated flags with food was carried out during no food (c) phase by flagging, but not supplementing with food in the SW sector in a 10×10 m grid.
  • Mean number of hedgehogs per scan and sector was compared between phases and months as was the distribution and aggregation of individuals in relation to different treatments.

Key results

  • Hedgehogs occurred at a mean density of one hedgehog per ha and were comprised of mostly transients which used the area only occassionally (average number of hedgehog days in study area = 3.74) and a few residents that used the area intensively. The distribution and overall abundance of these individuals was stable prior to experimental manipulations.
  • No significant differences between experimental phases but significant differences between sectors relating to food supplementation was observed indicating a significant change in the distribution but not density of hedgehogs in the study area as a whole.
  • The proportion of hedgehogs observed increased in areas supplemented by food but time taken for densities to increase/decrease in response to manipulations varied between sectors.
  • Individual hedgehogs altered their searching behaviour in response to food supplementation, showing a significant increase in the frequency of turns during and after food addition when this was randomly placed within the NE sector.
  • Hedgehogs persisted in their search for supplemented food after it had been removed and learnt the location of food supplemented sectors.
  • The flag test revealed that hedgehogs learned to associate visual cues with food.
  • The mean distance between individuals was 55.9 m and individuals did not aggregate in response to food supplementation but avoided other individuals up to a mean distance of 32.3 m (20-40 m).
  • No significant differences in weather conditions, which can affect earthworm availability, were observed during the study, suggesting the changes in distribution were not due to changes in natural resource availability.

Key messages to landowners and managers derived from these results

  • Food supplementation may provide a useful method for quantifying and monitoring changes in hedgehog abundance within areas.
  • Housing hedgehogs should consider social avoidance between individuals.

 

 

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