Guidance for detecting hedgehogs using footprint tracking tunnels

1. What they did

Hedgehogs are in steep decline in Britain, with at least a quarter lost between 2001 and 2011, yet they are hard to find because they are nocturnal and inconspicuous. This guide from the People’s Trust for Endangered Species (PTES) sets out a daytime method that anyone can use to tell whether hedgehogs are present or absent on a piece of land, whatever the habitat.

The method uses footprint tracking tunnels: light plastic triangular tunnels holding a removable tracking plate with two strips of “ink” (a mix of vegetable oil and charcoal powder on masking tape), a dish of hedgehog food in the middle, and paper sheets that record the footprints of any animal that walks through. The technique comes from research by Richard Yarnell, Phil Baker and The Mammal Society, funded by PTES and the British Hedgehog Preservation Society (BHPS).

The guide covers:

• Buying or making tunnels, with step-by-step instructions for making your own from corrugated plastic.
• The survey protocol and timeline, with a full equipment list.
• Where to put the tunnels.
• Setting up and checking the tunnels each day.
• Problems and how to deal with them.
• A footprint identification guide of life-size inked prints on paper.
• A recording sheet, health and safety advice, and a “do not disturb” sign.

2. What they found

The protocol

• If ten baited tunnels are set in up to one square kilometre for five nights in a row and no hedgehog footprints are found, the surveyor can be 95% sure hedgehogs are absent. The guide states this protocol was verified in a large field trial.
• The method cannot currently be used to estimate how many hedgehogs there are.
• Surveys can be done any time hedgehogs are active in the United Kingdom (UK), April to October. Each square kilometre takes 6.5 days: 1.5 days to prepare and pack up, and five days of surveying. All fieldwork is in daylight.
• Two people could survey two nearby square kilometre sites in about six days; more than that is not feasible.

Placing the tunnels

• Radio-tracking studies show hedgehogs use linear features to find their way, so tunnels go lengthways along hedges, walls, fences, field margins or the boundary between two kinds of vegetation.
• Tunnels should be spread evenly, at least 100 m apart, no more than two per field, with the entrances flush with the ground, and placed to avoid livestock and the public.
• Hedgehogs prefer to walk on short grass, then long grass, bare soil, crops, and last of all ploughed fields.

Checking the tunnels

• Tunnels are checked and rebaited every day. Morning checks keep prints in the best condition, especially in wet weather; evening checks may stop dogs taking the bait during the day.
• Prints of all animals are labelled and kept, the food is topped up, and damaged sheets are replaced.

Problems

Slugs eating the paper, livestock, wind, theft or vandalism, dogs and badgers can all damage tunnels or prints. The guide suggests early checks in wet weather, pegging tunnels down, signs on public land, and replacing or moving back any lost or moved tunnel and recording it.

Footprint identification

Earlier footprint guides were based on prints in mud, sand or snow, which look quite different from inky prints on paper. The guide shows life-size prints of adult and juvenile hedgehogs (front and back feet), several hedgehogs together, and hedgehogs alongside a cat, small rodents and a bird. It also shows prints of brown rat, domestic cat, grey squirrel, weasel, mink, common toad, polecat, badger, fox, rabbit, moorhen, stoat and unidentified birds.

3. What they concluded

• Footprint tunnels are, in the authors’ words, currently the only statistically robust way to tell whether hedgehogs are present or absent in an area, without the need for night work.
• Because hedgehogs can live at much higher densities in connected urban areas than in the countryside, it matters to know where they are and to consider them in land management and development.
• Since this is a new technique, the identification resources for animals other than hedgehogs will keep changing, and the guide points readers to the latest version online.

4. How tracking was or was not used

The whole method rests on tracks: animals walk over the ink and leave footprints on paper, and the surveyor identifies them. Presence or absence of hedgehogs is decided only from footprints. The guide includes an identification section for inked prints on paper, which look different from tracks in natural ground.

5. Tracker or observer certification

Not reported. The guide is written for anyone, including volunteers, and no training or test of footprint identification is described. The identification guide does not say who identified most of the prints; the polecat prints were verified by Johnny Birks (Swift Ecology), and the mink prints came from a captive animal at Wildwood.

6. Other technologies, skills or innovations

• Low-cost tunnels made from corrugated plastic, with home-made ink from vegetable oil and charcoal powder, and a sponge in a small pot used as an ink applicator.
• Velcro to fix the tracking plate, food dish and signs, so plates can be swapped between tunnels.
• A Global Positioning System (GPS) unit is recommended for mapping tunnel positions.

7. Implications for conservation (from the paper)

• Hedgehogs are declining across rural and urban areas at a rate the authors call unsustainable, and their future in the UK is increasingly uncertain.
• Hedgehogs eat a wide range of invertebrates and are indicators of a healthy natural environment.
• A reliable way to show absence as well as presence means hedgehogs can be considered in land management and during development.