Swans do not have many natural enemies, and are well equipped to defend themselves against most predators.
Threats to mute swans
The main predators are foxes, which from time to time take birds roosting in accessible places.
The main threats come from pollution of freshwater areas, lead weights previously used by anglers, fishing tackle, and overhead power lines. Vandalism is a problem in some areas.
A swan requires grit to break down food and may inadvertently take the small lead shot previously used by anglers as weights until its use was banned. Once retained in the gizzard, the shot will gradually be absorbed into the body and eventually lead to poisoning.
Although the use of lead shot as a fishing accessory is now illegal, a residue of lead is still to be found in some freshwater environments. This may cause a threat when old lead is exposed or brought within reach by receding water levels or disturbance of the sediments.
Entanglement in fishing tackle can also be a problem. Swans can swallow hooks ( the extraction of which is a potentially lethal operation for the birds) and nylon line presents its own problems. Anglers are encouraged by council bye-laws and the Anglers Code of Conduct not to discard used tackle but to take it home and cut it up or burn it.
Collision with overhead power lines is a major cause of swan mortality. If swans are regularly in collision with local overhead cables, speak to the Wayleave Officer of the relevant electricity company to see whether the cables can be made more visible to the swans by attachment of swan deflectors.