Most have generators, but when half the building is demolished you cannot safely run them... and add in the difficulty of getting more propane, or for the bigger ones most are run on diesel..... after storms like that... and you cannot run all the fans on those houses on one generator.. so they have to have one for every house or 2 houses... they use ALOT of electricity... my dairies often have generators so that if the power goes out they can run the milking system.... then as soon as it is shut down they can run the bulk tank cooler and the well pumps for water for the cattle... and then shut down something else to run the silo unloaders to fill the feed bunks... then shut that down to run more well water... and these are generators that are in the 20-80kw..... and they cannot run non-stop....forever....
Those fans are set up for what they call tunnel air flow... and have to exchange a certain amount of air per minute... If the air inlets are blocked or have dirt and debris from a storm, the efficiency is diminished greatly and the birds will not get the air exchange which also translates into cooling...
It is a very complicated and precise configuration when the houses are built... and if anything is off, it can affect the airflow and the heat in the building...
So, to say it is not an easy "they need generators" thing is so true... and I know you were not judging... there is so much that goes into figuring things like that. One reason that the birds are cheaper to raise in places like Fla and Ga is because it is cheaper to cool them with fans/airflow than it is to heat the houses in the winter like here... and once you have the well/infrastucture/ barns/sheds for feed and such, it is cheaper to add another house there than for another farm to start from scratch...
Nearly every single poultry building that is on my different dairies is an older one, and the newer ones are built in pairs now... more efficient to operate... and any that are adding do so in "2's"...
But generators cannot run at full capacity for days on end... and no one I know can afford enough generator capacity to run everything.,...believe me, many have systems that are designed to kick in as soon as the power goes out... but it is a stop gap measure and damage and devastation like from the hurricanes just taxes every single thing they do...