Haigh et al (2012) hedgehog investigating detecting hedgehogs
Title: An investigation into the techniques for detecting hedgehogs in a rural landscape, Journal of Negative Results, Ecology & Evolutionary Biology 8: 15-26. 2012
Authors: A. Haigh, F. Butler & R. M. O’Riordan
Background to study
Due to their nocturnal, secretive nature and small size, hedgehogs repeatedly go undetected in an area and this study investigates the effectiveness of five field methods for detecting hedgehogs.
- Five methods: Road kill surveys, questionnaire surveys, footprint tunnels, trapping and spotlighting were employed at up to six study sites in rural habitat in Ireland between April and June 2008 to assess the effectiveness of each method at determining the presence of hedgehogs.
- Sites were selected based on the possible presence of hedgehogs resulting from road kill sightings along a specified route and from questionnaires that identified the frequency, season and habitat of hedgehog sightings. Tunnels, trapping and spotlighting were then used to explore the presence of hedgehogs.
- 45 footprint tunnels baited with cat food were placed along hedgerows and edge habitat over 27 nights and within garden and farm habitat for a further 11 and 24 nights respectively.
- Sixteen rabbit traps were baited with cat food,placed along hedgerows at one site for 11 nights and checked daily at dawn.
- Direct searching using spotlights was carried out 2 hours after dusk for four nights a week, totalling 53 hours over 23 nights across five of the six study sites. In all instances, edge habitat was targetted.
- In addition, the seasonal detection of eight individuals, fitted with radio transmitters (attached using Velcro) as part of a wider study, was used here to a) determine when identifying hedgehog presence may be highest based on activity and b) to test if infrared thermal imagery could detect the tagged individuals.
- 145 hedgehogs were recorded as road kill during 2008 and, during the study period, road kill identified hedgehog presence at three of the six study sites where questionnaires also identified their presence. No live hedgehogs, however, were later detected using any method at these sites.
- Questionnaires had a 40% response rate and identified 10 habitats where hedgehogs were sighted, of which road verges (26%) gardens (25%) and hedgerows (21%) had the highest observation rate. Significantly more observations of hedgehogs were made between May and July (57%) and between midnight and 4am (44%).
- 6% of questionnaire respondents in one study area were unaware of hedgehogs despite their presence and farmer response suggested that hedgehogs used to be, but are no longer, sighted on farms.
- Trapping was unsuccessful at capturing hedgehogs or other animals.
- Footprint tunnels were not used regularly by hedgehogs, taking 48 nights on average to detect presence and at one site were not used at all and were avoided by a tagged individual being radio-tracked. 67% of footprints were from non-target animals and often footprints were obscured.
- Spotlighting was most effective for detecting hedgehogs taking, on average, 4 survey nights. At five study sites no hedgehogs were observed after a total of 53 hours of survey effort over a 23 day period.
- Radio collared hedgehogs had mostly been captured from spotlight surveys and were found to be most active during breeding season when loud vocalisations proved to be a good indicator of their presence.
- Tracking one individual allowed for a mean detection rate of 21 fixes per night and when scanning six individuals a mean of six fixes per night was attained.
- Infrared thermal imagery did not detect any hedgehogs even at a distance of 1 m from a tagged individual.
Key messages to landowners and managers derived from these results
- None of the methods proved to be soley effective at determining hedgehog presence and thus using multiple methods to confirm presence or absence of hedgehogs is recommended.
- Questionnaires and road kill surveys are a useful tool for identifying potential sites for presence and should be followed up using other detection methods, particularly spotlighting during breeding season and between 12 and 4 am when hedgehog activity is highest.