Many different types of animals, including birds, insects and small mammals can be encouraged to nest, roost or hibernate in urban sites by providing suitable homes. These artificial structures provide alternatives to homes in dead wood, mature trees, banks and other natural features that are often in short supply in the urban landscape. The cover provided by gardens, railway banks and other urban green space, together with higher temperatures and good food supplies can make some urban areas more inviting to wildlife than intensively farmed countryside. As well as their intrinsic value and interest, many of these species are ‘gardener ’s friends’, keeping in check slugs, snails and troublesome insects such as greenfly, and contributing to a more balanced ecosystem.
The construction of animal homes is a popular project with children. Many types of homes can be constructed out of scrap materials, or it may be possible to get donations of wood and other materials from local suppliers. Homes can be sited in school grounds, wildlife areas, private gardens or attached to buildings. Any site where there is a food supply and safety from predators or human disturbance may be successful.
Bird boxes
Properly designed and sited nestboxes can be extremely successful in allowing many species to nest and rear young. Such boxes are often much more suitable than natural sites, and are chosen by birds in preference, possibly due to better protection from predators which boxes offer.
Note the following:
- Wooden boxes should be made from wood that is preferably 25mm thick, with 17mm thickness the minimum. This thickness provides essential insulation from extremes of temperature. The construction must allow for sufficient ventilation and drainage.
- Thin plastic, wooden or hardboard boxes, sometimes seen on sale, are much too thin to provide sufficient insulation.
- Possibly the best boxes on sale are those made from ‘woodcrete’, which is a mixture of sawdust, concrete and clay. This material has excellent thermal properties and is virtually everlasting. Their quality is reflected in their high price of £20.00 upwards. For supplier see here.
- The size, aperture and siting of the box will determine which species are attracted. A ‘tit box’ is the easiest to construct, and in nearly all areas will be used by tits or other small birds. Open-fronted boxes should attract robins and other species. Creating artificial nesting sites for birds of prey is a more complex project, as the boxes are larger and more difficult to construct and attach. Sites must also be chosen carefully, and not all areas will support these species.
Wooden nest box for small species
This shows the basic design for a wooden nest box. The front opening can either be round, for tits and nuthatches, or open-fronted for other small birds. Use any untreated timber of adequate thickness, in a plank about 150mm wide, at least 17mm thick. The diagram shows the cutting pattern from a metre length of wood. If a longer piece of wood is available, the box can usefully be made taller by increasing the front, back and sides by 50mm. Pallet wood can be used, but the planks will have to be doubled up to give adequate thickness.
The hole should be 30-35mm diameter. Nuthatches may make the hole smaller by using mud. For an open-fronted box, cut the front panel in half.
The joints should be as shown, so they are exposed. Joints in contact with the tree or other support tend to stay damp. The nest is always made furthest away from the hole, so this design gives maximum depth front to back, keeping the nest well away from predators. nail together with panel pins, to prevent splitting the wood. The hinge can be made from a strip of cycle tyre stapled to the wood, or from sticky carpet tape. The open fronted box can have a nailed top, but still use a strip of tyre or tape to keep the box dry.
Siting nest boxes
- Nest boxes should be sited away from direct mid-day sun, and away from wet westerly winds. A south-east orientation is usually best.
- The height of the box is not significant, provided it is higher than 1.6m to be safe from ground predators. Where human interference may be a problem, site the box where it can only be reached with a ladder. Marsh and coat tits seem to like low boxes, only 600mm or so above the ground, concealed by foliage. Some woodcrete boxes are designed for hanging free from hooks or branches, which birds like, presumably because they feel safe from predation.
- If fixing to a living tree, attach with aluminium nails. These won’t rust, and can be removed even after many years. If left in the tree, aluminium nails will not damage any chain saw used on the timber. nest boxes can also be attached with twine or straps around the tree, but these must be checked each year and loosened as necessary to avoid strangling the tree.
- Open-fronted boxes need very careful siting if they are going to be used, as they give little protection against cats, squirrels, crows and magpies. Conceal them among shrubs and climbers. A ‘cage’ of 50mm chicken wire around the nest site may encourage birds to use the box.
Nest boxes are most likely to be used between late April and mid-June. Most small birds lay one egg a day for up to 14 days, with incubation taking about another 14 days. Some birds may have second broods. Remove old nests in autumn to prevent parasites persisting, but do not use any insecticide.
Larger bird boxes
Many other types of birds can be encouraged to nest by providing suitable boxes. Species include owls, kestrels, stock doves, jackdaws, house martins and swifts. kestrels are now common in many urban areas, and you may be lucky enough to attract a pair to nest on your site. The box should be open fronted, to the dimensions shown, with a lookout perch. kestrels like to nest high up, and the box should be over 7m from the ground, either attached to a building or tall tree. Site facing south-east, with a clear flight path.
The side batten type, with its deep recess, may also attract tawny owls, barn owls, little owls, mallard, stock dove and jackdaw. When fitted to a tree or pole, a side batten box is easy to inspect as a ladder can be rested next to the box.
The back batten type is only likely to attract kestrels, and allows easy viewing of the birds’ activities. Grey squirrels may take over both types of boxes. Prevent access by choosing isolated trees or poles, and then fitting a collar around the trunk or pole.
For further details see Nestboxes, du Feu, Chris, British Trust for Ornithology.
Bat boxes
Eleven of Britain’s fourteen resident bat species have been found to roost in bat boxes, and six species have used them for breeding. As many as 60 bats have been found gathered in a ‘nursery roost’ in one box, where the mothers gather to rear their young. The box should be large enough to allow a maternity colony to cluster together to keep the babies warm. The box may be used throughout they year, except in very cold weather (below -4°C).
Use untreated rough sawn timber, which allows bats to cling and crawl into the box. The timber should be at least 25mm thick, and the box carefully constructed to be rainproof and draught-free. Cut to the pattern shown, from a plank 150mm wide and 1100mm long. Fix together with waterproof glue and screws. The lid can be hinged and secured with hooks and eyes, or snapped into a groove on the back plate. ‘Woodcrete’ boxes can also be used, and in one study of bat behaviour, were found to be preferred to wooden boxes.
Site the boxes as high as possible in sheltered areas, where they are exposed to the sun for part of the day. There should be a clear flight path to the box entrance. A large tree can house up to three boxes. Attach with aluminium nails or straps. Boxes should not be disturbed, so check for occupancy by watching at dusk for bats to emerge.
Bat boxes are likely to be particularly valuable at sites where there is an ample food supply of insects, perhaps near a pond or waterlogged ground, but few existing mature trees or buildings for roosts.
The Bat Conservation Trust publishes a wide range of information, including details on improving bat habitats in gardens, protecting bats in churches, and various activities and projects for children.
Hedgehog houses
Suburban areas with gardens provide good hedgehog habitat, with plenty of cover and food available. In these sort of areas, hedgehog houses have a good chance of being occupied during the winter by hibernating hedgehogs.
Hedgehogs make hibernation nests of dry leaves, grass, bracken or other material, in dry snug sites under hedgerows, in hollows in banks, under piles of brushwood, bonfires, under sheds and so on. They can be encouraged by providing a sturdy box about 400mm square and 250mm high, with an entrance about 150mm in diameter and two side air vents, about 50mm in diameter. Very thick cardboard boxes or other unwanted containers are suitable, so long as they are reasonably sturdy. The box should be sited in a sheltered site, with the entrance facing south, preferably tucked under a hedge, large shrub or shed. Put some shredded newspaper and dry grass inside the box to start the nest. Cover the box with dry grass and leaves to insulate it, and then cover the mound with a thick plastic sheet, leaving the entrance accessible. Anchor the sheet down around the edges to keep the house snug and dry through the winter. Don’t disturb the box until late spring, when it can be checked for signs of occupancy. Renew the box as necessary.
A more permanent structure can be built of sound timber, stone, brick, paving slabs or other demolition material. The roof of the house must be removable to allow cleaning. If the mound is likely to be climbed on, you will have to make sure the structure is strong enough to withstand it. The mound can be disguised and access discouraged by growing ivy, dog-rose or similar over it.
Small mammals, reptiles and amphibians
Nooks and crannies in which these animals can hide, rest and hibernate are easily provided in a wildlife garden or habitat creation project. Almost any material which provides cover and shelter will be suitable, and the problem may be on some ‘derelict’ sites to improve the appearance of the site without clearing away many of these valuable features. Piles of rubble, timber, brushwood, broken down walls and rubbish can all provide cover, but may not look attractive. Balance these needs by building dry stone walls, revetments, Cornish ‘hedges’, rockeries and other built features, incorporating plenty of holes and hollows. Pile brushwood or timber in places where they will not attract arson. Any timber, building materials, drainpipes or items such as old flowerpots which can be safely left on the site can be stacked fairly neatly, and then simply left undisturbed. Sheet material such as old lino, carpets or corrugated iron will attract many types of small animals to shelter beneath. Leave some around if possible, in both sunny and shady sites. An anchored ‘trapdoor’ is very useful for sites visited by school groups. If the materials are available, a more attractive habitat can be provided by an area of raised stone or slab paving. Construct it on a sand base with blobs of mortar to secure the slabs, which will allow space for animals to burrow beneath. On the raised edge, leave plenty of gaps for access.
Invertebrates
Various materials can be used to provide nest sites for insects that are beneficial in gardens and wildlife sites.
Lone insects
Cut a plastic drainpipe to a length of about 180mm, and seal the end with a circle of polystyrene, wood or similar, taped to secure. A catering-size tin or clean paint-can may also be suitable. Using a hacksaw, cut bamboo canes of internal diameter 5-8mm into lengths slightly shorter than the pipe. Pack the canes tightly into the pipe so that the canes touch the blocked end. Site horizontally, as shown, in sunny positions in hedges or shrubs, or attached to tree trunks or fences.
Many insects make use of holes in timber, which in natural conditions are made by beetles for their brood cells. These holes can easily be simulated by drilling holes in timber posts or blocks. Fine-grained softwood or hardwood is suitable, depending on what is available. Drill as many holes as you like, of diameter 5-10mm, to the depth of the drill, but without going right through the wood. If drilling through hardwood, you will new, sharp drill bits, and take it slowly to avoid overheating the bit. Round or square posts of non-treated wood can be used, approximately 2m long by 100mm square, set firmly into the ground about 600mm.
Alternatively, use timber of 50 x 50mm or larger, cut into lengths of about 150mm. Drill into the end grain as shown. These can be sited individually, or taped together into bundles. Attach the blocks to walls, fences, or wedge them in the branches of shrubs and trees, in sunny, sheltered positions. Blocks can also be hung from branches of trees, on walls or buildings.
nests can be made of other hollow materials, including dry, hollow plant stems such as hogweed, bundles of straw, corrugated cardboard and drinking straws. Pack these into sections of drainpipe or plastic drinks bottles with the top cut off. Green lacewings, which predate on aphids, are especially welcome in gardens. Make a home by cutting the bottom off a plastic drinks bottle, and inserting a roll of corrugated cardboard, cut about 25mm shorter than the bottle to keep it dry. Leave the bottle top on, and hang the bottle near a window or external light which will attract the lacewings. Position it by August, and leave in place over winter.
Bumblebees may form colonies in suitable sites where there are plenty of food plants available. A variety of containers can be used, so long as they are dry, insulated, ventilated and left undisturbed. The container can be placed above or below ground, with the entrance protected from mice by 10mm wire mesh. An old mouse nest placed inside will encourage nesting. Alternatively, some down from an old pillow is suitable, but don’t use kapok, as the bees get tangled up in it. Sometimes bumblebees or wasps will colonise a bird box, using the remains of the previous year’s nest.
