Lethargic ducklings dying!

[SoggyForks]

One of my fawn and white runner ducklings is being super lethargic. I had another one acting this way the other day and she died - does anyone know what to do? She doesn't feel very warm so I brought her inside but I don't know what's happening!

 

[SoggyForks]

Update - she's a bit more lively but still very tired. Any advice would be helpful. I have her with some wet foot and water and a heating pad.

 

[SoggyForks]

Update: she died peacefully in my arms a couple of minutes ago.

 

[Wyorp Rock]

I'm sorry to hear about your Duckling.

I don't know anything about Ducks, do you have any others that are having issues? If so, @Miss Lydia or @Jenbirdee may be able to offer some care tips.