Size: Male swans are typically larger than females. This difference is most noticeable in the mute swan, where males can be up to 20% larger than females.
Neck length: Male swans also have longer necks than females. This difference is most noticeable in the black-necked swan, where males can have necks up to 20% longer than females.
Bill color: Male swans typically have a brighter bill color than females. This difference is most noticeable in the trumpeter swan, where males have a bright orange bill while females have a more muted orange bill.
Head shape: Male swans often have a more angular head shape than females. This difference is most noticeable in the whooper swan, where males have a more square-shaped head while females have a more rounded head.
Body shape: Male swans typically have a more muscular body shape than females. This difference is most noticeable in the black swan, where males have a broader chest and more muscular wings than females.
It is important to note that these are just general trends and there is some variation within each species. For example, some female swans may be larger than some male swans, and some male swans may have a shorter bill color than some female swans.