Swans are among the largest and most recognizable waterfowl, known for their powerful presence on lakes and rivers. Successful reproduction requires an intensive commitment from the adult birds, spanning territory establishment, nest construction, and the lengthy process of incubation. Incubation is the period of intense focus where parents sit on the eggs to protect and warm them until they are ready to hatch.
Defining the Incubation Period
The incubation period is the time required for the embryos to fully develop. For the common Mute Swan, this period spans between 35 and 42 days. The female, known as the pen, maintains the necessary temperature and humidity by pressing her specialized brood patch—a featherless area of skin—directly against the eggs for maximum heat transfer. She also regularly turns the eggs with her bill, ensuring they are heated evenly and preventing the embryo from sticking to the shell membrane.
A typical clutch size ranges from five to nine large eggs, all of which must be kept at a consistent temperature. Incubation officially begins only after the final egg in the clutch has been laid, which synchronizes the development of all the embryos. This ensures that all the young swans, called cygnets, hatch at roughly the same time, allowing the family to leave the nest together.
The Nesting Cycle Leading Up to Incubation
The actual sitting period is preceded by a preparatory phase that takes several weeks. Swans select a nest site close to the water’s edge, often in a concealed area among tall reeds or dense vegetation for protection. The pair then constructs a massive, platform-like nest from materials like reeds, grasses, and sticks, which can take up to ten days. The male, or cob, typically gathers the bulk of the material while the pen arranges it into the final structure.
Once the nest is ready, the female begins the egg-laying process, producing one egg approximately every 24 to 48 hours. The pen performs some brief, intermittent sitting during the laying phase. However, the constant, dedicated period of incubation only starts once the entire clutch is complete.
Parental Roles During Incubation and Hatching
During the weeks of incubation, parental roles are clearly divided to maximize the safety of the nest. The female performs the vast majority of the sitting, often remaining on the eggs almost continuously, only leaving briefly to feed or preen. Because she rarely leaves, the pen can lose a significant amount of her body weight over the course of the incubation period.
The male does not possess a specialized brood patch like the female, but his role as protector is paramount. The cob aggressively guards the territory, patrolling the surrounding water and driving away any perceived threats. He remains close to the nest to ensure his mate’s safety and will occasionally sit on the eggs for a short time if the pen needs a break.
Post-Hatching Duties
Once the cygnets hatch, usually within a single day, the parents shift their focus to brooding the young and leading them into the water within 48 hours. Both the cob and the pen then share the duties of feeding the young by pulling up underwater plants and providing constant defense for the family.