Design for Biodiversity

A Technical Guide for New and Existing Buildings

Kelly Gunnell, Carol Williams, Brian Murphy

• Publisher: RIBA Publishing
• Year: 2019
• ISBN:
  9781000705126
• Edition: 1
• Topic: Architecture
• Subtopic: Architecture générale

The built environment has the potential to have a major impact on biodiversity, not least with the increasingly demanding requirements to design more energy efficient and airtight buildings, leaving less space for species to inhabit. The construction industry has an important role to play in ensuring that buildings are designed and refurbished in a way in which biodiversity can be enhanced.

Through written guidance and architectural drawings, this book advises on how to incorporate provision for biodiversity within developments. With sections on different building-reliant species, general principles for design, ready-made products that be incorporated into designs, and legislation, policy and regulations, this book is an invaluable resource for all architects, ecologists and anyone involved in designing or briefing for biodiversity in buildings.

Chapter One
Biodiversity and the importance of buildings

1.1 Building-reliant biodiversity

As our buildings and developments have crept over the landscape, some animal species have adapted to share our built structures with us in order to survive, and have done so for a very long time. Some of these animals have come to depend on buildings for their survival. We term them ‘building-reliant species’. This book focuses on how to maintain and enhance our buildings for building-reliant species, such as some bat and bird species. However, there are a large number of other organisms, such as some insects and plants, that make use of our built structures and we can easily enhance buildings to meet their needs.

As our landscape is set to become increasingly urbanised over the next 50 years it is more important than ever to ensure there is provision for wildlife in our built environment; for building-reliant species, their very survival depends on it.

This chapter gives a general introduction to the ecology of bats, birds, invertebrates and plants and the ways in which they use buildings.

1.2 About bats and buildings

1.2.1 Bats worldwide

There are over 1,200 species of bats worldwide, which make up a fifth of all mammal species. Bats can be as small as a bumble bee or as large as a small dog. On a global scale, bats are one of the most widely distributed groups of mammals. They are found across every land mass, apart from the Arctic, the Antarctic and a few isolated oceanic islands. There are bats in the far north of Scandinavia, as well as in the deserts of south-west USA.

Bats are most numerous in the tropics. The majority eat insects, but some feed on pollen and nectar, while others eat fruit. A few highly specialised species feed on fish, frogs and even on other bats. There are also the three species of vampire bats, found in Central and South America, that feed on blood. Globally, bats play a vital role in our environment, being responsible for seed dispersal, pollination and pest control in forests, in agriculture and in the wider landscape.

Approximately 25% of the world’s bats are threatened with extinction.

Natterer’s bat in brickwork

1.2.2 Bats in the UK

Seventeen species of bat breed in the UK. They are all small, nocturnal and eat insects, although the habitats in which they find their insect food and the types of insect they eat vary between species. All the UK bats have reasonable eyesight, but when flying and looking for insect prey in darkness it is their ears that are most important. To navigate and hunt for insects they use echolocation; by shouting at a high pitch (above our hearing range) and listening for the returning echoes, the bats create a very clear picture of their surroundings and of the location and direction of movement of insects.

The insects on which British bats feed cover a wide range, depending on the size of the bat species and the habitats in which they feed. The hunting methods of UK bat species therefore vary depending on the habitats in which they specialise. The larger UK bats can feed on beetles as big as May bugs and dung beetles, while the smaller bats are likely to feed on smaller insects, such as gnats, crane flies and midges, of which a single bat can consume around 3,000 in one night. Unsurprisingly, bats are most likely to be found feeding over habitats that support a good number of insects, such as any body of water, native woodland, hedgerows, unimproved meadows and grassland, mature gardens and grazed pasture, where dung fauna are important. Table 1.1 gives a summary of the annual cycle of UK bats.

Table 1.1 Annual cycle of UK bats

Season	Activity
Autumn	The young born this summer are feeding independently All bats are feeding to put on weight for the winter Mating begins
Winter	Hibernation (consisting of prolonged bouts of torpor) Bats (particularly small species) feed during mild spells
Spring	Hibernation ends and females become pregnant In late spring females gather in maternity roosts, which need to be warm Non-breeding adults are found as individuals or in small numbers in cooler roosts
Summer	The young are born Each mother has a single baby which suckles for four to five weeks

Bats do not make nests but use existing spaces to roost. These roosts must have the right climatic conditions, they must be dark and they must be free from disturbance. Bats use roosts to shelter during the day, to hibernate, to raise young and for mating. Roosts vary in size; some are used by a single bat and some by hundreds. Bats use different roosts at different times of the year, and they tend to return year after year to the same roosts in buildings, which they may have been using for generations. Bats are long lived, with some UK bats having been recorded living into their thirties in the wild. However, having only one young per year means that bat populations are very slow to recover from any changes to the environment that adversely impact them, such as the loss of prey species or the loss of roosts, which threaten their ability to survive or breed.

All UK bat populations have declined considerably during the past century. In recent years some species have shown small increases in population, but more sustained increases are needed before any populations recover. The declines were largely due to human factors – such as the loss of feeding habitats; the use of pesticides and intensive farming practices, which reduce the abundance of insects; and building and development work, which affects roosts – and these declines are the reason why all UK bats and their roosts (even when bats are not present) are now protected by law (see Chapter 2).

Brown long-eared bat

1.2.3 Importance of buildings for bats

All UK bat species will make use of buildings on occasions, but for some species buildings are essential as roost sites. This situation has arisen over a long period of time, as tree cover and the availability of caves, which would have provided natural roost sites, have become scarce. Hundreds of years ago bat species adapted to share our built structures with us.

One of the factors that make buildings suitable for bats is the ability of built structures to provide a stable microclimate. Temperature plays a key role in roosting ecology and selection. That need differs based on the time of year and the sex and species of the bat. For several weeks in the summer, female bats choose somewhere warm to gather in maternity roosts, such as in a roof space heated by the sun or in features in a wall that is south-facing. At the same time, non-breeding adults find cooler roosts, such as north-facing features, where bats are found in small numbers or singly. In the winter, bats of both sexes choose somewhere cool with high humidity to hibernate. This is generally in underground sites, such as caves and tunnels but also cellars and ice houses.

Lesser horseshoe bats in roof void

Bats are often found roosting in buildings. Both new and old buildings are used by bats, although a greater number of roosts and wider range of species are found in older structures. Some species will roost in internal spaces, such as within the roof void or within a cavity wall, but others will tend to use external features, such as hanging tiles, weather boarding, fascias, soffits and barge boards. Bats do not take any material into the roost with them, nor do they chew wires.

When considering the roosting habits of bats in buildings, it is useful to make an arbitrary division between those crevice-dwelling species that roost in external features or that only require a small crevice type of provision within the structure, and those bats that require flying space within the building. A further distinction is needed within the group of bats that require flight space, based on access to the roost: this is because horseshoe bats have different needs to all other UK bat species.

The greater and lesser horseshoe bats are the only two species of bat in the UK that have adapted to hanging free by their feet when roosting. These two bat species, which have a very close association with buildings, are among our rarest species – whose numbers have suffered the steepest decline, although both species have shown signs of a reverse of that trend in very recent years (see Bat Conservation Trust, 2012). Their range within the UK has also been constricted and they are currently only found in Wales and south-west England. Horseshoe bats’ adaptation to hanging free by their feet has resulted in a specialisation of their leg structure, which means that they are unable to crawl very effectively – unlike all oth...