When large tracts of forest are swallowed up by urban sprawl, or when households replace tall grass with artificial turf or rehabilitate buildings to repair cracks and crevices, wildlife populations are deprived of potential sites to rest, breed and winter. For this reason, conservation groups are urging homeowners to create wildlife-friendly habitats on their own land whenever possible.
One artificial refuge that has graced gardens for a long time is the bird box. It is estimated that there are 4.7 million of them in gardens across the UK. Some studies have reported that nest boxes (or bricks) can help birds produce more chicks and increase their populations compared to birds nesting in areas without artificial shelters.
But whether and how animals actually use these retreats depends on their design, location, and wider landscape conditions. In the wrong environment – or with the wrong design – wildlife can be harmed or put at increased risk of being caught by predators.
Relatively little is known about what makes a house a home for species other than birds, or how effective artificial refuges are for species conservation. Still, garden centers and other retailers offer a wide variety, ranging from ceramic houses for toads to wooden and concrete roosts for bats. Many of these are made and installed with mammals in mind.
One such mammal is the nocturnal, ground-dwelling hedgehog. Hedgehogs have experienced a long-term decline and are listed as Vulnerable on the UK Red List of Mammals: In some parts of the countryside, numbers may have fallen by as much as 75% in the last 20 years. Hedgehogs often use residential gardens where populations exist, and here the public – through the provision of nesting boxes (or “hedgehog houses”) – could play an important role in their conservation.
In a recent study, I found that you may be able to improve the chances of a hedgehog taking up residence in your garden nest box by, among other things, carefully considering where you position them and leaving out food and bedding.
The hedgehog census
Charming images and videos of hedgehogs using nest boxes (both homemade and store-bought) abound on social media. Yet very little is known about how best to select, craft, or install these sanctuaries. That’s partly because people are advised not to disturb nesting hedgehogs.
To solve this problem, researchers from the University of Reading (including myself) and specialists from the conservation campaign group Hedgehog Street launched the Hedgehog Housing Census: an online questionnaire that collected information on how nest boxes are used in the UK.
More than 5,000 surveys were returned. Using this data, we examined how hedgehogs use boxes for different types of nesting. Hedgehogs typically build different nests to rest during the day, raise young and hibernate over the winter, and may move between more than one nest at a time. For each nest type, we modeled how the use of a nest box appeared to be influenced by its design and dimensions, as well as garden and environmental characteristics.
For most seasons, the study showed that hedgehogs were more likely to have used a nest box that contained food – such as B. meaty animal feed – and bedding were provided. Some gardeners left heaps of dry leaves in a corner of the garden for hedgehogs to collect and drag into the box.
Hedgehogs were also more likely to use nest boxes where there was access between the front and back yards, emphasizing the importance of connections between habitats. This can be done by cutting a hole in the bottom of a fence or leaving a gap under a gate to form a hedgehog road. In addition, the likelihood of a hedgehog inhabiting a box tended to increase when placed under shelter such as shrubs or on hard surfaces such as patios and entrances faced away from wide open spaces.
The presence of dogs only seemed to have a negative impact during the sensitive hibernation period, which typically occurs between November and April. Surprisingly, badgers or foxes didn’t seem to deter hedgehogs from nesting in a box, although few people reported seeing either species in their yard. We also found that nest boxes were used more frequently during hibernation when the nest boxes were south-facing and less than five meters from a building. This may be because these spots were warmer, and cozier nest chambers help hedgehogs use less energy during hibernation. However, too warm and hedgehogs could wake up more often. The optimal nest box temperature for hedgehogs – and the design features that might affect this – is not well understood.
The census also revealed where in gardens hedgehogs may prefer to build their own nests. Respondents to the survey reported 2,546 other nests used by hedgehogs in their gardens, including nests hidden under vegetation such as long grass or shrubs (46%), sheds (21%), piles of wood (15%) and compost heaps (6th %) ) and decking (6%).
Nest boxes – and gardens more broadly – provide important nesting habitats for the declining hedgehog. But there’s still a lot we don’t know about how these artificial havens compare to natural nests. This is an area that researchers need to delve deeper into by unraveling how nest box design affects occupancy and by attempting to assess the consequences of using artificial shelters on hedgehog health, behavior and abundance to understand. For now, it’s clear that simple actions can improve a hedgehog’s chances of using a nest box – a potentially critical part of encouraging recovery of this species.