Do you have a muscovy? I wouldn't try trimming the nails there is alot of blood if you cut the quick. you could try filing I have never done it with any of mine. https://www.backyardchickens.com/t/750869/raising-and-caring-for-ducklings#post_10611711 heres a great link on raising and care of ducklings.
Grit not pebbles, or sand. can you find play sand the kind that you put in a kids sand box? or bird grit doesn't your parakeet have to have grit? mine did.
Day old magpies.
Sounds like you have adults, when she lays an egg take it and either eat it or bake something with it, you can use them the same as chicken eggs, Do you have a secure building for them to sleep in? Ducks make nice tasty dinner for alot of animals including the family dog or neighbors dogs so protecting them during the day and especially at night is very important, How long have you had them? they need clean bedding and plenty of clean fresh water deep enough to dunk their heads into to wash out their noses and eyes, never feed them without giving them adequate water to wash it down, they like water to bath in so a plastic kiddy pool will make them happy just try to keep the water clean which is really hard since they like to make it muddy in the first 15min you gi ve it to them, [just their nature] They need fresh nutrious feed appropriate for their ages, alot of us feed and all flock food and laying ducks need extra calcium and we use Oyster shell given separate from their feed. are they living inside a pen? or can they free range around your yard or acreage?
