Two very different adult sizes in one breed
A fully grown Muscovy drake commonly weighs 10 to 15 pounds, while a fully grown hen weighs about 6 to 8 pounds, roughly half her mate. No other common domestic duck shows such a gap between the sexes. The drake is a long, horizontal, broad-breasted bird with a bare red face and heavy legs; the hen is a comparatively neat duck who happens to share his colouring and caruncles. Anyone choosing the breed should picture the drake's size first, because he sets the requirements for space and handling.
A perching duck built on a different plan
Muscovies descend from a tree-perching South American species, and their adult build still shows it. They carry strong clawed feet for gripping branches, broad wings they genuinely use, and a long tail quite unlike the upturned tail of pond-bred ducks. That ancestry explains both the drake's muscular weight and the breed's surprising agility: a 12-pound drake can still get himself onto a low roof or fence rail, and hens fly considerably better than that.
Housing and handling for the largest backyard duck
Pens for adult Muscovies need stout construction. Gates, latches, and fencing that would shrug off a 5-pound duck get leaned on, perched on, and tested by birds two to three times that weight. Low, wide roosts suit their perching instinct better than floor-only housing, and they should be built to take a drake's full weight without springing. For handling, slide one hand under the breast and support the body properly; a big Muscovy lifted carelessly by the legs or wings can injure itself struggling, and his claws are not decorative.
A slower road to full size
Muscovies take their time compared with fast-growing meat ducks. Hens approach adult weight over their first breeding season, while drakes keep adding breadth and mass well past the age when a Pekin would be finished. Judging a young drake at four months against the full 10-to-15-pound range will undersell him. Steady growth, good feather, and bright behaviour matter more than hitting a number early, but a bird of either sex that stops growing entirely deserves a check of feed quality and worm burden.
One flock, two pen problems: hens that fly, drakes that lean
The size split creates opposite management problems under one roof. Hens at 6 to 8 pounds, with those broad perching-duck wings, can fly out of pens that hold every other duck breed, so Muscovy keepers either net the run, clip one wing, or accept hens roosting in the rafters and trees. Drakes present the reverse problem: too heavy to fly meaningfully, they test fences by weight, shoulder through weak gates, and can be injured if they attempt drops from perches a hen takes easily. Setting low roosts the drake can hop onto, rather than high ones only hens can reach, keeps his joints and feet out of trouble.
Keeping weights straight across a mixed flock
In a flock where the biggest bird weighs more than double the smallest, memory is a poor record keeper, and weight changes in an individual bird are easy to miss. Noting each Muscovy's settled adult weight, and rechecking the drake before breeding season and the hens after sitting, gives you a baseline when a bird later looks light. KinsLe's Pet Passport gathers every bird's identity, adult weight, and health notes into one portable packet, so the drake's 14 pounds and the hen's 7 never blur together when records are needed.