Getting to know the dabblers

Dabbling ducks feed by tipping forward on the surface, head and neck below the water, tail in the air, rather than diving. On a British reservoir, gravel pit or flooded meadow in winter, four species turn up again and again: mallard, gadwall, pintail and teal. Learn three things about each — bill shape, speculum colour and feeding posture — and you will be able to name most of the ducks in front of you, even in flat winter light.

The speculum is the patch of coloured feathers on the trailing edge of the wing. It is often hidden while a bird sits on the water, so train yourself to check every duck that stretches, flaps or rises. That brief flash of colour is one of the most reliable field marks you have.

Mallard: the yardstick

The mallard is the duck everything else gets compared with, and it is worth learning properly rather than dismissing. The drake is unmistakable: glossy green head, chestnut breast, grey body and those curled black feathers above the tail. The female is mottled brown with a dark eye stripe, and is easily confused with several other brown ducks.

Bill shape: the drake's bill is a plain yellow-orange with a black nail at the tip. The female's is orange with dark markings along the top. Both are broad and heavy.

Speculum: iridescent blue-purple, boldly bordered with white on both the front and rear edges.

Feeding posture: a deliberate, heavy upender, tail high, often in the shallows or on flooded grass. When a group of mallards tips up together, it is a good sign you are in the right sort of wetland.

Gadwall: the understated grey duck

Gadwall is the one many birdwatchers overlook. The drake is finely vermiculated grey-brown with a black rear end and a chestnut patch on the shoulder. Look for the steep forehead and the rather small, dark grey-black bill, which is shorter and more delicate than a mallard's.

Speculum: a clean white panel, shown by both sexes. That white wing patch is the clincher. The female gadwall resembles a small, dark female mallard but has a whiter belly and the same white speculum.

Feeding posture: gadwall often feed at the surface with just the head submerged, picking food from the top layer of water rather than plunging deep. They frequently work in pairs or small parties, and can look almost dainty beside a big drake mallard.

Pintail: the long-necked one

The pintail is the elegant one. The drake has a chocolate-brown head, a white stripe running up the back of the neck, a grey body and that long, pointed tail. The bill is slate-blue with a black line along the top, a very useful mark at range. The female is slender and grey-brown, with a grey bill, a long neck and a pointed tail of her own.

Speculum: dark green-bronze with a white trailing edge, and the drake also shows a pale cream or buff panel on the inner wing bordered with black.

Feeding posture: the pintail's long neck lets it upend in deeper water than most dabblers. Watch for birds swimming forward with the head just beneath the surface. They often feed further out than mallards, so scan the open water as well as the margins.

Teal: small, quick and noisy

Teal is our smallest duck, and once you have the size in your eye, you rarely mistake it. The drake has a chestnut head with a green eye patch, a grey body and a bold vertical white stripe on the breast. The bill is short and dark grey-black.

Speculum: dark green with a buff or cream border, shown by the female as well as the drake.

Feeding posture: teal prefer the shallowest margins, dabbling in mud or dipping just below the surface. They can upend, but usually do not need to. A flock takes off almost vertically, and the whistling call of the drake is one of the sounds of a British winter marsh.

Sorting them on the water

Put the three marks together and most birds resolve quickly.

• Bill: mallard yellow-orange, gadwall short and dark, pintail slate with a dark top line, teal short and dark.
• Speculum: mallard blue-purple with white both sides, gadwall plain white, pintail green-bronze with a white trailing edge, teal green with a buff border.
• Posture: mallard a heavy upender, gadwall a surface dabber, pintail a deep upender, teal a shallow margin feeder.
• Size and shape: teal tiny, pintail tall and slim, gadwall compact and steep-faced, mallard bulky.

Visit the same hide through the winter and you will start to recognise individuals by their habits as much as their plumage. Take your time, check the wing-stretchers, and let the posture tell you what you are looking at before you reach for the speculum.