There are a lot of ducks with ducklings at the moment in the park near my house, but one duck wanders around with 13+ ducklings. Can they lay that many eggs at one time or is she looking after ducklings that don’t belong to her? They are all the same species but not the same size, which suggests that some are younger than the others.

why-animals-do-the-thing:

I can’t give you a specific answer without knowing your location and the species of duck, but it looks like most species of common ducks in the US and UK lay an average of 8-10 eggs, with some laying almost double that. It makes sense to lay so many, if you think about it, because ducklings are fairly helpless fluffy snack-sized nuggets for the most common predatory animals. 

It doesn’t sound like it’s common for wild ducks to adopt orphaned ducklings, according to the rehabber sites I found – apparently you can sometimes get domestic ducks to foster abandoned ducklings, although you have to have babies of almost the exact same age. 

Mama ducks have a lot of babies. 13+ is vaguely unusual but not too out of the ordinary.