Dead 2 week old babies

[sle62]

I just completed my nest check and found 4 dead babies, all about 2 weeks old, with swollen bellies and no sign of trauma. Three were in one condo, together with 3 live babies who look healthy, and 1 in another condo with 4 healthy looking babies. The live and dead ones had their beginning feathers and color. They were still soft, but very stinky. This is the first time in 5 years of seeing this. We had a really nice, cooler spring in SE FL but very little to no rain. and the canals are very low. Anyone have a speculation as to what would have caused this? I am speculating not enough food and water since there are still healthy looking babies in there.