There’s a Shelduck walking on mud at RSPB Lodmoor. It’s sinking gently, despite its webbed feet, into the black ooze. It’s a heavy duck:
Shelducks were previously called Sheldrakes, at least they were until the late 19th Century. Quite what changed their sex remains a mystery to me.
The males and females appear identical to humans.
I’m sure Shelducks and Sheldrakes know the difference.