You can usually tell by if it is a loud quacker or if it whispers. Loud ducklings are usually female and the drakes are quieter. Eventually the drake feather will curl up and that is the best way to tell. Cute duckling
You might want to see if you can get your duckling another duck buddy his/her own age. Ducks like to be in groups, and while chickens are better than no flock at all, your cute little Pekin may have identity issues when it gets older. If it turns out to be a drake, it could try to mate the chickens, which could kill them. They also love to muck up the water; chicks are much tidier.
I raised my muscovy duck Ivan with chicks his own age. He grew much faster than they did and at first was their "protector." But then he became mildly aggressive; by then the chicks were big enough to go to the "Big Chicken" pen. Ivan never became friends with the Pekin ducks that were slightly older and he shows almost no interest in the muscovy hen I got to be his girlfriend. He prefers to hang out with chickens during free range time, and often challenges the top rooster in a most brutal way, evn though I think I made it clear to Ivan that the hens are not his. He needs to be completely supervised when with them. He is also very bonded to me. It's very cute the way he follows me around and relaxes in my lap, but I can't help but feel Ivan just doesn't know how to be a duck.
So if possible, please get your adorable duckling a buddy; it doesn't have to be another Pekin but one about his/her own age is good. It shouldn't matter if they both turn out to be males if there's no female to fight over. If you end up with a male and a female you can have baby ducks or just take the eggs. And two females mean lots of eggs to eat.
Ducks are soooooo much fun, as you can tell from this forum.
As for sexing by quack sound, try picking your duckling up and listening to its protests. It's getting to the age where its quack is evolving from a baby squeak. The girls will have more of a honking sound as their voices are changing. The males have a wimpy little quack that doesn't generate much volume.
thank you, I am going to go back and get another one, she is so sweet and folows e everywhere. I am in love wirh her already.My kids named him/her mingming. Right now she is still peeping like a chick but louder and higher pitched.