Canada Goose

Start with the head. A black head and long black neck carry a white band that wraps under the chin like a strap, all above a brown body. Only two other geese share that pattern.

Size helps too. At 75 to 110 cm, it is on average the largest of the true geese. Males average 3.9 kg and females 3.6 kg, and the female, about a tenth smaller, looks virtually the same.

Odd birds turn up. Some have a brown or pepper-speckled neck, thought to be leucistic; others show dark cheeks or a white forehead.

The Barnacle Goose is the look-alike you are most likely to meet. It is clearly smaller, with a tiny stubby bill, more white on the face, a black breast and a silver-grey rather than brown body.

Cackling Geese have counted as a separate species since 2004, and in Britain since 2005. Most are much smaller, the tiniest barely bigger than a Mallard, with a stubbier neck and bill. The smallest Canada Geese overlap with the biggest Cackling Geese, so a mixed flock can still defeat you.

The ‘honk’ belongs to the male. The female's ‘hrink’ is similar but shorter and higher, so a pair calling together gives a two-tone exchange. Researchers recognise ten calls in all, each tied to a different situation.

A hiss is a warning. An agitated goose opens with a high hiss, then stands tall, spreads its wings and may charge, pecking or striking with the wings. Parents with goslings will do this to people.

For a long time the geese stayed on country estates, kept for ornament and shooting. In 1953 the British Isles held between about 2,670 and 10,090 birds, depending on who counted, and in the 1970s they spread across the countryside.

Numbers reached roughly 60–64,000 by 1990, then 82,000 by 1999. Moving pairs away from farmland in the 1950s and 1960s only seeded new colonies. The Midlands and the South East remain strongholds, but moorland, upland waters and towns now have geese too.

Reservoirs and flooded gravel pits created nest sites, the Mute Swan is its only serious rival, and most European birds have lost the urge to migrate. Big flocks can push native ducks and swans off nest sites, overgraze water plants and enrich the water with droppings.

Pairs form in the second year and usually last for life. The nest is a shallow hollow lined with plant matter and down, normally on raised ground near water.

The female incubates for 24 to 32 days while the male stands guard. Adults moult their flight feathers during breeding and are grounded for 20 to 40 days, flying again at roughly the moment their young do.

Goslings walk, swim and feed themselves from hatching. Look for a family in single file, one parent at each end, and for crèches where several broods merge. In Europe, mink, otters and Mute Swans take eggs and young.

Present all year, since most birds in Britain no longer migrate. Spring and early summer are the nesting and gosling months, when parents defend nest and goslings most fiercely.