Water

Chickens go through a lot of water--or a lot of water goes through them. It stands to reason, especially for layers, since an egg is mostly liquid, but broilers drink a lot too. I remember reading somewhere that layers who want for water more than so many hours may stop laying abruptly and if the want is longer, they may quit laying for good. I let my broilers run out of water one hot day last summer. Creatures of habit, they drank from the dry bowl as though there was water, raising their heads occasionally to swallow, but there was nothing but air rolling down their extended gullets. I quickly filled the bucket and thanked my lucky stars that none had died. After all, it had been dry only a few hours. The next morning, two big cockerels lay dead in the pen, victims of stress no doubt.
The point is that chickens must never want for water. A chicken that has wanted for water is a time bomb. It may survive the initial stress, but it will always be compromised and is not likely to perform satisfactorily, and if there's anything worse than a broiler dead at 4 pounds it's a broiler dead at 5 or 6 pounds.
The old theory that dinosaurs were cold-blooded reptiles has been overturned. According to prevailing thought on the subject, chickens (along with other birds) are the closest living relatives of dinosaurs. You can't watch chickens dusting themselves without thinking about dinosaurs. The abrupt extinction of dinosaurs 65 million years ago continues to perplex scientists to this day. Some think a meteor or other extraterrestrial object may have struck the earth and put so much debris in the air that the sun was blocked and all plant life died, subsequently killing all the plant eaters. But not everybody is convinced. Even if plant life was disrupted, much of it survived the event or it wouldn't be here today. Other creatures survived too, including some small mouse-like mammals that evolved, eventually, to Homo Sapiens.  In the short term, meat eaters like T-Rex might have survived by eating the dead and dying, but they were driven to extinction too.
Could it be that the catastrophic event put so much dust into the atmosphere that Earth's temperature plummeted for a short period--just long enough to drive the surface temperature down far enough to freeze fresh water on the entire surface--kind of a nuclear winter? If so, sea creatures would likely survive,  in the deep, along with burrowing creatures that could wring enough moisture from the earth to survive, and plant life would begin again to flourish as the dust settled, just as dormant plants re-awaken in the spring. Hunger might have been an issue for some creatures, but creatures that required lots of water on a regular basis would have died out quickly, possibly within days, long before the food ran out. Carnivores, omnivores, herbivores, would have suffered equally at a frozen lakeside--especially those with a low tolerance for water deprivation. I wonder if they went through the motions of drinking to the very end.