Ask an expert: swan behaviour

John asked: why do swans roll to the side when in the water.

Mute swans, our most common UK species of swan, are usually found on lakes, rivers and canals. Yet despite their size, they are without doubt a highly graceful species on water. Though they look rather ungamely and awkward on land, swans acan engage in some rather bizarre looking activity whilst in the water and I suspect this is what John may have witnessed.

It is rare to see an unkempt swan, and in order to keep their feathers in tip-top condition swans regularly bathe and preen. Using an oil-producing gland at the base of their tail, swans use their bills to spread this oil throughout their feathers to keep them waterproof. This activity involves much wiggling about, as well as throwing their head back across their body to get to those trickier to reach feathers. When bathing swans may splash about or simply open their wings and dive underwater, before rolling along the surface of the water. To dry themselves off, swans simply flap their wings and shake their bodies.

Most swan courtship display is also carried out on water and is equally noticeable . The pre-mating display, for example, involves synchronised head dipping, preening and the rubbing of back and flanks. Once mating has occurred, the pair will rise out of the water together, their necks extended and chests touching, before engaging in up/down and side to side bill movement. This is followed by further bathing, preening and ends with a flourishing tail wag. Outside of the breeding season, chin lifting with an erect neck is often a good indicator of a family greeting. In antagonistic behaviour where a threat is perceived by either the male or female, the head is laid back, secondary feathers are raised and the neck feathers are fluffed up. Wing flapping can also serve as a threat display. Such behaviour is common place throughout the breeding season, as well as when such birds are approached by a potential predator.