Why These Summer Visitors Need a Hand

Swifts and house martins arrive each spring from central and southern Africa, crossing deserts and oceans to raise a family in the British summer. Both are aerial insect-eaters, and both have become far scarcer in recent decades — swift numbers have more than halved since the mid-1990s, and house martins are in steep decline too.

The reasons are practical rather than mysterious. Renovated roofs, sealed soffits, PVC fascias and tidier eaves have removed the crevices and overhangs these birds rely on. Meanwhile, the insects they feed on have thinned out, and dry summers leave house martins short of the wet mud they need to build. The good news is that a single household with the right setup can genuinely add nesting places to a street or village.

Telling Your Swifts From Your House Martins

It pays to know which bird you are trying to help, because their housing needs are quite different.

• Swifts are dark, cigar-shaped birds with long scythe wings, usually seen screaming in fast parties high overhead on summer evenings. They never perch and never land on the ground. They arrive in early May and are gone by mid-August.
• House martins are much smaller, with glossy blue-black upperparts, a brilliant white belly and a white rump that flashes as they fly. They arrive from mid-April, often raise two or three broods, and may still be around into early October. They build cup-shaped nests of mud pellets plastered under the eaves, and they like company — colonies of a few pairs are typical.

If you already have either species nearby, work with the wall they are using. Birds return to the same colony year after year, and new boxes placed close to occupied nests are far more likely to be found.

Swift Boxes: High, Dark and Unobstructed

Swifts need height and a clear drop so they can launch themselves into the air. Aim for a box fixed under the eaves at five metres or more above the ground, on a wall with open space in front — never above a balcony rail, hedge or fence that would block the exit path.

• Choose a box with an internal floor around 30cm by 15cm and a shallow oval entrance roughly 6.5cm wide by 3.5cm high, placed near the bottom edge of the front panel.
• Site it in shade, ideally on a north or north-easterly aspect. Swifts suffer badly in boxes that bake in afternoon sun.
• Fit a nest brick, or a box fitted flush into the wall, if you are building, extending or re-roofing — integral nest places last for the life of the building.
• Be patient. It can take a few seasons before a new box is found. Playing swift calls near the box on summer evenings during May and June can help passing birds notice it.

House Martin Cups: Shade and Good Neighbours

House martin nests sit tight under the overhang, protected from rain, usually between two and six metres up. Ready-made cups in the same position work well, and they are best fixed in groups of three or four, spaced about half a metre apart, under a wide eave on a shaded wall.

Avoid a south-facing wall that takes the full midday sun — young birds can overheat in a shallow cup. Put up a small droppings board about 40cm below the nests to catch the mess, and clean it once the birds have left. Do not paint or repair fascias and eaves between April and September if you can help it.

Mud on Tap

House martins need a steady supply of wet mud in late May and June, and each nest takes hundreds of beakfuls. In a dry spell, a tidy garden can be a builder's yard with no materials.

• Leave a patch of bare, clay-rich soil in a border and keep it damp with a watering can each evening.
• Make a shallow muddy puddle in a tray or an old washing-up bowl sunk into the ground, topped up daily.
• A pond with a gently sloping, unlined edge gives the same result and benefits everything else in the garden.
• Avoid sandy or gravelly soils for nest-building — add a bag of clay or topsoil to a corner if your ground is light.

Insects, Timing and Living Alongside Them

A nest is only half the job; the birds need food within a short flight of home. Plant native flowers such as ox-eye daisy, knapweed, bird's-foot trefoil and clover, let a patch of grass grow long, and put a small pond in a sunny spot. Above all, stop using insecticides, including on roses and fruit trees — every aphid is a meal for a growing brood.

Once the birds move in, the main task is simply to leave them alone. Keep ladders, drills and window cleaners away from active nests, and remember that swifts and house martins are protected by law while nesting. Starlings and house sparrows may investigate your boxes; this is normal, and swift boxes with a low entrance are less attractive to them.

Finally, enjoy the noise. The screaming parties over a summer evening, and the chatter of a busy colony under the eaves, are among the best signs that a British garden is doing something right.