Hedgehog Friendly Campus is a programme delivered by our core staff at SOS-UK and is partially funded by public donations, and the British Hedgehog Preservation Society. As part of Hedgehog Awareness Week earlier this month, we're excited to share the programme's mission of empowering students and staff to protect hedgehogs and other wildlife whilst educating their local communities. In this special guest blog, Project Coordinator Henrietta Pringle from PTES discusses the brand new National Hedgehog Monitoring Programme!
Want to join in on creating a hedgehog-friendly world? Reach out to the team at info@hedgehogfriendlycampus.co.uk to find out how you can get involved!
A new national Hedgehog survey
Despite being one of the nation’s most-loved mammals, we lack robust knowledge of hedgehog population trends and their abundance across the country. What we do know makes for fairly grim reading; according to the most recent State of Britain’s Hedgehogs, published in 2022, we’ve lost up to three-quarters of our hedgehogs from the nation’s countryside over the last two decades. The picture in urban settings is looking brighter with signs that populations in our towns and cities are stabilizing, or even recovering after a long period of decline. However, as with most mammals, the picture for hedgehogs is far from clear, as the data underpinning current estimates and trends have limitations. People’s Trust for Endangered Species and The British Hedgehog Preservation Society, in partnership with Nottingham Trent University, Zoological Society of London, London HogWatch, Durham University and MammalWeb, are launching a new National Hedgehog Monitoring Programme (NHMP) to help bridge this gap.
Why do we need to know how many hedgehogs there are?
Population estimates should act as a foundation for conservation efforts, as they provide a baseline against which we can compare future trends and measure progress. Put another way, monitoring hedgehog numbers, and how they change over time, gives us warning if the population is in trouble. For surveys that tell us only where hedgehogs are present, we don’t know how that population is faring until it has disappeared, when it’s too late. Armed with information on number of hedgehogs, and crucially where, or in which habitats they are declining (or indeed recovering), we can inform targeted conservation efforts.
Why don’t we already know how many hedgehogs there are?
Being nocturnal, surveying hedgehogs is challenging. Traditional methods are labour intensive (e.g. searching by spotlight), or require capturing hedgehogs to mark them to make them individually recognisable once released. While the surveys that employ these methods provide local population estimates, these are small scale studies, so we can’t assume these numbers are representative of trends across the country.
National hedgehog data come from ad hoc records, where members of the public report their sightings (Hedgehog Street’s Big Hedgehog Map). Although these records are valuable in telling us where hedgehogs are, they don’t necessarily tell us where hedgehogs are absent. Because these records don’t have any associated effort data (how long the animal was looked for, or if it was looked for at all), we don’t know whether gaps in the map reflect true hedgehog absences, or an absence of people looking for hedgehogs. The way to overcome this is through standardised surveys, where everyone adopts the same methods, employing the same amount of effort so we can be more sure that variation in results is due to real variation in hedgehog densities.
Hedgehog data from standardised surveys do exist, where surveyors monitor the same route or site for a set period of time on a regular basis (e.g. BTO’s Breeding Bird Survey, PTES’s Living with Mammals). However, these often rely on spotting signs of hedgehogs (e.g. droppings). Whilst this is very useful in providing data at a national scale and from the same sites every year, many hedgehogs will be missed. That’s why we’re piloting the NHMP, a new standardised national survey dedicated to hedgehogs.
What’s different/new about this survey?
The availability of affordable, good quality trail cameras has opened up new monitoring possibilities for nocturnal species and those harder to detect by traditional methods. The NHMP is a national camera-trapping survey which uses robust analytical method that allows estimation of population density from imagery. Previously, estimating population density using cameras has only been possible for species with recognisable unique features (e.g. tigers with their stripe patterns). For other species where individuals cannot be identified, camera-trapping has provided simply more and better data on presence or absence.
The NHMP uses the Random Encounter Model (REM), which eliminates the need to recognise individuals. Instead, the number of times a species of interest is detected by cameras across a site is converted into a population density by taking into account the animal’s speed of movement, its activity rate and the detection zone of the camera. To calculate these parameters, at each camera siting, we create a map of the field of view, to relate pixel position to the animal’s real world position on the ground. The method has been tested on tigers, wild boar and deer, and small-scale studies have shown that REM-derived hedgehog population estimates are comparable to those derived from more traditional methods. Recent adaptations of the REM method mean that we can now apply this to a citizen-science programme.
How can you help?
The NHMP relies on volunteers to deploy cameras at a network of sites across the country, in a range of habitats. At each 1km2 site, 30 cameras are set up, and left for 30 days. We’re working with organisations across the country to act as regional hubs that can coordinate the monitoring at several sites. NHMP sites so far include several university campuses: Nottingham Trent, Durham, Lancaster, Sheffield, Cardiff, Sussex and UCL, so there will be opportunities to help with camera deployment at those sites, as well as with local Mammal Groups and Wildlife Trusts.
One of the challenges of the project will be dealing with the volume of images that are captured by the cameras. Before the data can be analysed, all the images with hedgehogs (or other species of interest) will need to be identified. Thirteen sites were surveyed last year, generating over 2 million images, so left to one or two project staff members, this would take months of processing time alone! Instead we’re using MammalWeb, an online platform for collaborative monitoring of mammals using camera traps. New AI tools will be used to filter out images that contain humans and any blank images caused by false triggers, but we need help from the public to identify the animals in the remaining images. You can sign up to MammalWeb now and view images from our pilot sites deployed last year. By tagging the species you see, you can directly contribute to this ground-breaking project, from the comfort of your home! It’s a really fun process and can get very addictive! As well as hedgehogs, we’ve had sightings of stoats, badgers, buzzards and barn owls, so you never know what you might see. The first images from this year’s sites are being uploaded as we speak. To find out more and to sign up, visit this website.
