Wildlife Crafts: Build a Weatherproof Kestrel Nest Box for Your Garden

Few birds give themselves away as readily as the kestrel. A bird hanging into the wind over a roadside verge, head locked on the grass below, is a kestrel more often than not. If you have rough, tussocky ground within a field or two of your garden, it is worth giving one somewhere to nest. Kestrels do not build nests; they want a cavity, a ledge or an old crow's nest, and those are in short supply in a tidy landscape. A well-made box, fixed high enough and sited with a bit of thought, can fill that gap for years. It will not work everywhere, though, so read the siting notes before you pick up a saw.

An Honest Test of Your Site First

Kestrels hunt voles, mice and large insects over rough grassland, field margins, young plantations and unkempt verges. If your view is mown lawn, tarmac and close-board fencing, a box will most likely sit empty or be claimed by stock doves.

The strongest candidates are gardens on the edge of farmland, allotments with scruffy corners, smallholdings, school grounds with a wild area, or anywhere with a paddock, railway embankment or set-aside strip nearby. Watch for hovering birds through the winter. Kestrels hold territories all year, so a bird working the same patch in January is a good sign. It is also worth asking about neighbouring land — permission to mount a box on a barn gable is often easier to get than people expect.

Dimensions and Materials

The traditional kestrel box is tall and narrow, with a round entrance hole near the top of the front panel. A hole of about 75 mm suits a kestrel and is too small for a barn owl or tawny owl, which keeps your paperwork simple and avoids turf wars.

• 18 mm exterior-grade plywood or 20 mm rough-sawn softwood — roughly 1.5 m² in total
• Galvanised or stainless steel screws, around 40 mm, plus exterior wood glue
• Roof covering: an EPDM offcut, roofing felt, or a piece of slate
• Fine mesh for ventilation slots, and 6 mm drainage holes in the floor
• A brass hook and eye or turn button for the access panel
• Water-based exterior stain for the outside only — never creosote or solvent preservative inside the box
• Dry wood shavings or coarse sawdust for the base

Cutting list

• Floor: 300 × 300 mm
• Back: 300 mm wide × 450 mm high
• Sides: two, 300 mm deep, 450 mm high at the back tapering to 380 mm at the front
• Front: 300 × 380 mm, with a 75 mm entrance hole centred about 90 mm below the top edge
• Roof: 360 × 400 mm, so it overhangs on every side

Building the Box

1. Cut the panels and dry-fit them. Predrill every screw hole, especially near the edges of plywood.
2. Cut the entrance hole with a 75 mm hole saw, or chain-drill and file it smooth. Rough edges wear feathers.
3. Cut three or four narrow ventilation slots high in each side, then staple mesh over them from the inside. Drill four 6 mm drainage holes in the floor corners.
4. Glue and screw the back, sides and floor together, keeping the inside free of protruding screw tips.
5. Fit the roof with a slight fall towards the back, so rainwater runs away from the entrance rather than into it. Fix the covering now, with clouts that do not poke through into the nesting space.
6. Make one side hinged for cleaning, and add a batten over its top edge to stop rain running in. A hinged roof works too, but it is heavier to manage one-handed on a ladder.
7. Sand sharp edges, leave the inside bare, and add no perch — kestrels do not need one, and it gives predators a foothold.
8. Spread about 50 mm of dry shavings in the base. Kestrels bring no nesting material of their own; they scrape a hollow in whatever is there.

Weatherproofing Without Trapping Damp

A sealed box sweats. Air has to move through it, which is why the ventilation slots and floor drainage matter as much as the roof. Treat the outside with a water-based exterior stain so the timber can still dry out, and leave the inside untreated.

Pale colours are better than dark ones. A dark box in full sun can become uncomfortably hot, and heat is a bigger killer of chicks in a British summer than most people assume. Check the roof covering each autumn; a leaky roof is the single most common reason these boxes fail after a few seasons. If the box sits on a pole, make sure water cannot run down the pole and into the floor — a small drip collar, or simply raising the box on battens, sorts it.

Mounting: Height, Aspect and Fixings

Three to five metres above ground is the sweet spot. Higher on a building gable is fine; anything below two metres is a cat's playground.

Face the entrance between north-east and east. That keeps it out of the prevailing south-westerly rain and away from the fiercest midday sun, while still giving the birds a clear flight line. Keep about a metre of clear air below and in front of the entrance so nothing can launch at it from a branch.

Fix the box with two brackets rather than one so it cannot rock in a gale, using galvanised or stainless steel fixings. On a tree, strap or bracket the box rather than nailing into the trunk, and check the fixing each year. On a post, a treated 75 mm timber or a scaffold pole with a smooth metal collar at about 1.5 m will deter most climbing predators.

Cleaning, Timing and the Law

Open the box in late October or November, once the breeding season is well over. Clear out old pellets, fur and insect debris, and replace the shavings with fresh dry material. Wear gloves and a dust mask; dried droppings and old nest material are unpleasant to breathe in. Kestrels generally lay from April into May, so any maintenance should be finished by the end of February.

If a bird is sitting, close the box and walk away. Kestrels, their nests and their eggs are protected under the Wildlife and Countryside Act 1981, and disturbing an active nest is an offence. If you need to work near one — roof repairs, tree surgery, a survey — take advice from a licensed ecologist or the relevant statutory conservation body before you start.

Jackdaws, stock doves and grey squirrels will all investigate a vacant box. Clear out an empty box in early winter, before the nesting season begins, but once anything is nesting in it, leave well alone.

Details That Make the Difference

Keep a simple record: the date you put the box up, what used it, how many young fledged. Two years of notes tells you more about your site than any general advice can.

If nothing has shown interest after two full springs, the problem is almost certainly the setting rather than the box. Try another position with more open hunting ground,

Photo: MabelAmber / Pixabay