Two small brown birds are hopping about under the feeder, and you are not quite sure which is which. House sparrows and dunnocks share the same patch of lawn, the same appetite for small seeds and crumbs, and the same general look: a brownish bird with a shortish tail and a busy manner. Get your eye in, though, and they are as different as two garden birds can be — one loud, stocky and sociable, the other slim, grey and secretive.

Why these two get muddled

Both birds are roughly sparrow-sized, with the dunnock slightly the smaller and slighter of the two at around 13–14 cm against the house sparrow's 14–16 cm. Both spend much of their time on or near the ground, both eat seeds and small invertebrates, and both have brown, streaky backs that blend into soil, twigs and dead leaves. Seen briefly through a kitchen window, in poor light, at a distance, they can look interchangeable.

They are not close relatives at all. The house sparrow is a weaver finch, a colonial seed-eater built for cracking grain. The dunnock is the only British member of the accentor family, a group of small, quiet, ground-dwelling birds of scrub and hedgerow. Once you know that, the differences in shape and behaviour start to make perfect sense.

House sparrow: stocky, noisy and sociable

• Build: chunky and full-bodied, with a large head, short tail and a hunched, almost neckless look when perched.
• Bill: thick, deep and conical — a proper seed-cracking tool.
• Male: grey crown, chestnut-brown nape, black bib and greyish cheeks.
• Female: plain buff-brown, softly streaked, with a pale stripe behind the eye and no grey on the face.
• Voice: constant chirruping, cheeping and chattering, especially in a group.

House sparrows are rarely alone. They arrive as a gang, squabble over the feeders, dust-bathe in dry soil, and roost together in dense cover. They are tied to buildings for nesting, tucking into gaps under eaves, loose roof tiles, vents and old martin nests, and they will readily use a sparrow terrace or a cluster of boxes. They are also, sadly, far less common than they were a few decades ago, so a busy flock is worth celebrating.

Dunnock: slim, grey and quietly mouse-like

• Build: slender and neat, with a fine, pointed bill and relatively thin, pinkish-brown legs.
• Plumage: slate-grey head, face and breast, contrasting with a warm brown, dark-streaked back.
• Movement: creeps and shuffles low along the ground, often with a nervous flick of both wings and a twitch of the tail.
• Voice: a thin, high "tseep" contact call, and a bright, hurried, tinkling song delivered from a hedge top.

Watch a dunnock for a minute and the word that comes to mind is discreet. It works the shadowy edges of borders, slips beneath shrubs and rarely flies up to a hanging feeder. It is often in pairs, and in spring its song is one of the earliest and most persistent in the garden — a rapid, cheerful jumble that lacks the rich, rolling phrases of a robin.

Behaviour clues that settle identification

When plumage is ambiguous, let the bird's habits decide it for you.

• Company: a crowd of chirruping brown birds means house sparrows. One or two silent birds under the hedge means dunnocks.
• Feeding position: sparrows pile onto hanging feeders, bird tables and rooftops. Dunnocks pick over the ground, the lawn edge and the ground tray.
• Feeding style: sparrows grab, husk and bicker; dunnocks peck delicately at small seeds, crumbs and suet granules.
• Movement: sparrows bluster and hop, half-opening their wings in scraps. Dunnocks shuffle, crouch and flick.
• Noise: if the garden sounds busy all day, that is the sparrows. If it goes quiet and then a thin note comes from deep in the shrubs, that is the dunnock.

Telling a female house sparrow from a dunnock

This is the pairing that trips most people up. A female house sparrow is plain buff-brown and unstreaked beneath, but she keeps the thick, deep bill and the chunky, big-headed shape. A dunnock has a fine, narrow bill, a distinctly grey face and breast, and clear dark streaking across the back. Juvenile sparrows in summer can look frustratingly dunnock-like — streaky and plain — but they still have that heavy bill and sturdy build. If in doubt, wait for the bird to turn side-on: the bill profile gives the game away almost every time.

Making your garden work for both

• Keep a ground feeding tray or scatter a little seed and suet crumb under a shrub, well away from the cat's favourite ambush point.
• Leave a strip of leaf litter, moss and untidy hedge base — dunnocks feed and nest low, and a neat, bare border offers them nothing.
• Plant or keep dense low cover such as ivy, hawthorn, berberis or honeysuckle for nesting and shelter.
• For sparrows, provide holes: a sparrow terrace, a cluster of small boxes, or safe gaps under the eaves.
• Offer sunflower hearts, millet and mixed seed for the sparrows, and small amounts of mealworm for the dunnocks.
• Keep feeders clean and rotate feeding sites so the ground beneath does not become sour.

Give it ten quiet minutes with a cup of tea and the birds will sort themselves out for you. The chunky one with the thick bill and the loud opinion is a house sparrow; the trim grey one slipping quietly along the border is a dunnock. Once you have made that distinction, you never really lose it — and you will notice far more of what is going on in your garden as a result.