Birds
Swan
Cygnus · also called swans
A swan is a bird built right up against a physical limit. At 12 to 15 kilograms the largest species are about as heavy as a flying animal can be, which is why a swan has to sprint across the water to get airborne. On the water, though, that size makes it the dominant bird of the pond — a long-necked grazer that will hold a territory and defend its family against almost anything.
Overview
Swans are the genus Cygnus, six or seven species across the temperate and subarctic Northern Hemisphere plus South America and Australasia. They are the largest waterfowl, close relatives of geese and ducks in the family Anatidae. Northern swans are all-white as adults; the black swan of Australia and the black-necked swan of South America break the pattern. All feed mainly on water plants.
The neck
A swan has 22 to 25 neck vertebrae — against seven in a giraffe — and uses that reach to pull up plants over a metre down by upending, deeper than a dabbling duck can manage without diving.
Family life
Swans usually pair for years, often for life, renewing the bond each spring with synchronised displays, and both parents incubate and guard the brood. Cygnets swim within a day but ride on a parent’s back for warmth in the first weeks. A defending adult hisses, spreads its wings, and strikes with the bony wrist knob — enough to knock a person down or swamp a small boat, though the “can break your arm” claim is not well supported.
Flight, and the lack of it
A heavy swan needs a 30 m water runway to take off. During the annual moult every swan drops all its flight feathers at once and is grounded for weeks, and a few species barely fly at all.
Status
Swans as a group are Not Evaluated. Most are secure or increasing — the mute swan is common and locally invasive in North America, and the trumpeter swan recovered from near-extinction to tens of thousands. The main threats are lead poisoning from spent shot and fishing weights and power-line collisions.
Swan: common questions
Do swans really mate for life?
Mostly, though it is a strong tendency rather than an absolute rule. Swans form pair bonds that commonly last many years, and a large share of pairs stay together until one partner dies, then the survivor usually finds a new mate. The bond is renewed each breeding season with courtship displays, and staying paired has clear advantages, since an experienced pair that already knows a territory raises more young. Divorce does occur, most often after a season in which the pair failed to breed successfully, and rates vary between species and studies. So the popular image of lifelong swan devotion is broadly accurate but not universal.
Can a swan break your arm?
Almost certainly not, despite how often the claim is repeated. A swan defending its nest or cygnets is genuinely intimidating, hissing, rearing up, beating its wings, and striking with the bony knob at the wrist joint, and it can bruise you, knock you down, or capsize a canoe. But its bones are light and partly hollow and its wing is not built to deliver a bone-breaking blow to a human. The realistic risks are falling awkwardly while backing away, being pushed under the water, or being repeatedly struck about the head. The sensible response is simply to leave the area, especially during the spring and early summer breeding season.
Why do swans need such a long runway to take off?
Because they are close to the maximum weight at which flight is possible. Lift depends on wing area and airspeed, and a 12 to 15 kilogram swan does not have enough wing to leap into the air from a standstill the way a small bird can. Instead it must build up speed, and it does this by running across the surface of the water while flapping hard, using its large webbed feet to push off each stride, often for 30 metres or more before it has enough airspeed to lift clear. This is also why swans favour large open lakes and why they can become stranded on small ponds, wet roads, or playing fields that look like water from above.
What is the difference between a swan, a goose, and a duck?
They are all in the waterfowl family Anatidae, arranged roughly by size and proportion. Swans are the largest, with very long necks, heavy bodies, and, in the northern species, all-white adult plumage. Geese are intermediate, with shorter necks, stouter legs set forward for walking and grazing on land, and no strong colour difference between the sexes. Ducks are the smallest and most varied, with short necks, and in many species males and females look very different. Swans and geese tend to have long pair bonds and biparental care, while many ducks pair only for a season and the female raises the brood alone. The three groups grade into one another and are not sharply separated.