Why Swifts Are Struggling

Swifts are the last of our summer migrants to arrive and the first to leave, appearing over British towns and villages from late April and gone again by the middle of August. They spend almost their entire lives on the wing, feeding, sleeping and even mating in the air, and they touch down only to breed. That single need — a dark, safe cavity in a building — is becoming harder to find. Renovations, roof repairs, loft conversions and modern building methods have sealed up the gaps and crevices under eaves that swifts have used for centuries. The result is a serious decline: swift numbers in the UK have fallen by well over half in the last three decades, and the species is now red-listed as a bird of the highest conservation concern.

A garden nest box will not solve that on its own, but it is one of the most direct and effective things an individual can do. Swifts nest in loose colonies, so every occupied box helps to keep a local population going — and once a pair takes to a site, they tend to return year after year.

Choosing the Right Box

Swifts cannot perch. Their tiny feet are built for clinging to vertical surfaces, not for landing on a branch, and they enter the nest by flying straight at the entrance and slipping inside. That means an ordinary garden bird box is useless to them. You need a purpose-built swift box, and it should have:

• A shallow, wide entrance — roughly 65 mm across and 30 mm high — set at the bottom of the front panel, not a round hole.
• A long, narrow internal space, around 30 cm long, 15 cm high and 15–20 cm wide, so the birds can shuffle along rather than turn around.
• No perch below the entrance, which would only give predators a foothold.
• Ventilation and drainage, plus a removable front or side panel so you can inspect and clean it.
• Durable materials — exterior-grade plywood, or a wood-concrete composite, which lasts far longer and holds a steadier temperature.

Some designs include an internal baffle or a short entrance tunnel, which keeps the nest chamber dark and discourages starlings and sparrows from taking over.

Siting and Fitting the Box

Height and aspect matter more than anything else. Fit the box as high as you safely can, ideally at least five metres above the ground, and tuck it under the eaves or tight against the wall just below roof level. Swifts need a clear, unobstructed approach, so avoid positions where trees, wires or a neighbouring wall block the flight line in.

Orientation makes a real difference. A box facing north or east stays cooler, whereas one in full sun from midday onwards can overheat, especially in a hot July. If you must use a south or west wall, choose a spot shaded by the eaves or by foliage. Try to keep the box away from directly above a door, window or path, because the droppings below an active nest are considerable. Never mount a swift box on a tree — it needs the solidity and shelter of a building.

Encouraging Swifts to Take Up Residence

Patience is essential. Swifts are strongly faithful to their nesting sites, and young birds spend their first two or three summers prospecting for a place of their own. A new box may sit empty for a season or two before anyone moves in.

You can speed things up considerably by playing swift attraction calls. These are recordings of swifts screaming in flight around a colony, and they draw curious birds down for a look. Play them from early May through to early August, in short bursts at dawn and dusk, at a volume that mimics a real group of birds rather than a loudspeaker. Stop as soon as birds begin investigating regularly, and never play calls where swifts are not already seen overhead.

Inside the box, add a shallow layer of dried grass, a few feathers or a purpose-made nest cup. Swifts do gather nesting material, but a small amount of soft lining gives them a head start and makes the cavity feel more like a nest than a box.

Looking After the Box Through the Year

Once swifts have left in August, the box can be left undisturbed until winter. A quick check in late autumn or early spring is plenty: clear out any old nesting material, remove debris or dead insects, verify that the drainage holes are clear, and repair any cracks or loose fixings. Do not use insecticides or wood treatments inside the box.

Keep an eye on the entrance for signs of squatters. Sparrows and starlings will happily move in, and while they are welcome in their own right, they will block swifts out. If a wasp nest appears, leave it until the colony dies off in autumn before clearing it away.

Small Changes That Make a Big Difference

Swifts hunt on the wing, taking tiny flying insects — aphids, beetles, flies, midges — high in the air. Anything that reduces insect numbers reduces their food supply, so cutting out garden chemicals, leaving a patch of long grass, and planting nectar-rich flowers for pollinators all help indirectly. A garden pond, however small, will produce insects too.

It is also worth looking beyond the box. If you have a loft, a loose tile or a gap under the eaves that is not causing a problem, leaving it be could preserve a natural nest site. New extensions and roofing work can be an opportunity to fit an integrated swift brick into the wall itself, which lasts as long as the building. And if a neighbour fits a box too, so much the better — swifts prefer company, and two or three occupied boxes on one street are far more likely to draw in new pairs than one on its own.

Even if your box stays empty the first summer, keep it up. Swifts are long-lived and loyal, and the birds prospecting your roofline this year may well be the ones nesting there the next.