Cause of death to my chick?

[Tinychickenfarm]

This is day three with new chicks and ducklings. We bought 11 chicks and three ducklings and have been keeping them together in a very large brooder tote.
This is my second time brooding chicks.
They are under a heat lamp and seem to have the appropriate temperature in their brooder. I have a starter crumble and water available to them 24/7.

Yesterday evening, I noticed one of my chicks was acting lethargic. It looked like she was starting to fall asleep while standing like they sometimes do when they are this young, but this was how she stayed. Did not wake up and become active like the other chicks do.
Even when she would take a couple steps, she kept her eyes closed and seemed to be off balance.

I mixed up some chick saver electrolytes and got her to drink a fair amount of this by dipping her beak in.

Today she seemed about the same. I put her in a separate box so she was not bothered by the other chicks and ducklings and softened the starter crumble for her to drink/eat.
She took one bite this morning, but the rest of it has just been me getting her to drink the broth of it.

She seemed to be doing about the same today. Mainly sleeping standing up, but then an hour ago I noticed she laid down. It seemed that she was breathing slightly quicker/bigger breaths, but it did not seem labored and no noisy breathing.
I don’t believe she was too warm. The other chicks are under the same heat and doing great.

I heard some activity in her box and it was a single flail, a few seconds apart, about three or four times.
After that, she was gone

This is my first time with a chick death, so I want to try to figure out most likely cause in order to prevent any others if possible.

Again- no visible signs of illness that I could tell, besides lethargy and seemingly off balance.


Any feedback is appreciated. Thanks.

 

[Tinychickenfarm]

Update- using the pellets for bedding, and she did seem to be sort of “fluffed up” while standing around.
I did see one poop today, and it looked like normal stool.

 

[coach723]

Chicken chicks and ducklings should be brooded separately. Ducks like water, and tend to make a mess with it, which is not good for chicken chicks, it can lead to illness (a warm, wet brooder is prime for disease) or getting chilled.
Having said that, do you know how old the chicks are? In the first week, and sometimes the second, you can lose them to what is called "failure to thrive". There may be internal issues that are not apparent immediately after hatch, that show up as they start to grow, usually unknown, and they just don't make it. It happens. There is also shipping stress that can happen when they are sent from the hatchery to where ever you bought them. That can be too much for some of them. When they are so small, it's often very hard to know.