Are Muscovy males bigger than females as ducklings?

Hello! So, two weeks ago now I adopted two Muscovy ducklings. At the time they were approximately a week old, and I had selected them based on their foot/leg size vaguely hoping to have a male and female but not really counting on my questionable method.
Recently I noticed one of the two (the presumed female) has been sleepier than the other, plopping down for a nap during outside time while the chicks and other duckling played and explored. I started paying ridiculously close attention for any sign of illness, and I have discovered that she is quite a bit lighter in weight than her presumed-male counterpart. "He" has indeed developed thicker legs than her and seems to be bigger every time I check on the brooder. She eats and drinks and flaps and runs around, but the fact that she is smaller, growing slower and is more prone to naps and yawning has me a little worried!
My question to you wise duck experts is, could at least the weight difference be caused by gender? Is a sleepy three-week-old something to worry about or am I just overreacting? My chicks are always funny about naps when they are that age but somehow I feel like my little ducks are more delicate! (Help me)
Any sage words of advice are much appreciated.
(Chocolate is "male" yellow/white is "female," and the pictures do not illustrate what I'm talking about at all but they're really cute so enjoy)

Yes,drakes are largeer than femals,even as ducklings,drakes grow faster than a duck.They end up as twice the same size of ducks

Actually i've had many females be bigger than males as ducklings and then even a few be bigger at juvenile development, but they around the end they stopped growing and the males grew much bigger than them in the end, so no, not all male ducklings are bigger than females. A lot of the time you just have to wait if you can't tell by personality

The size of the duckling is limited to the size of the egg - not the gender of the duckling. Initially ducklings grow at the same rate, but then Muscovy drakes hit a growth spurt.