I've been on this site for many years. Over that time, there have been a few cases such as this where the entire flock died suddenly and all at the same time. Fortunately, in most of those other cases, the OP stuck around and provided clues as we offered suggestions. In this case the OP skipped out early, likely because they had no flock left to warrant further participation on BYC. So we don't have all the clues we could have had.
Of those past cases, there was one where an adjacent work shop with gasses and chemicals in use accounted for the sudden death of the entire flock as the toxic fumes permeated into the coop.
Another flock was lost from contaminated ground water from adjacent fracking by petroleum companies. The water was so poisonous they were forced to flee their home for a year.
Another case where all the chickens died suddenly had hung a red heat lamp that was teflon coated to prevent shattering. The poisonous gas killed every chicken, and they were huddled together in one spot just as this flock.
One tragic case involved a coop fire where the chickens all died of smoke inhalation. They were also positioned all together as this flock was, on rooster died trying to shelter the hen next to him with his wing.
In all cases where an entire flock was killed that involved a predator, the scene was one of mayhem, blood and gore and feathers and dead bodies scattered all over. Or just one chicken per night mysteriously disappeared until the cause was discovered to be a stealth predator.
In cases where toxic mold or rat poison was involved, it sickened some chickens, killed some, and left some survivors.
It's my belief that if the OP of this thread were to return, we would likely find out there was some sort of environmental factor involved in the uniform and sudden death of this flock. While it's still a broad category, an environmental cause is the only one where it would be possible for every single chicken in the flock to die at the same time without a mark of injury on the bodies.
I'm even going to stick my neck out and speculate that the OP did finally discover the cause of death and was too upset they accidentally set their flock up to be poisoned and were too embarrassed or grief stricken to continue the thread after losing their entire flock to ignorance or carelessness, deciding to just walk away and put the nightmare behind them.
