Dredging up this thread because I have something important to add that not many people have thought about - how lawn mowers, log splitters, any machine that leaks petroleum distillates onto the soil can kill chickens as easily as if you exposed them to insecticides.
A couple days ago, I lost a four-week old chick. I discovered it just as it was beginning to show signs of neurotoxin poisoning. It was having trouble standing and maintaining balance. Within an hour, it was having trouble holding its head up, and it had lost the ability to drink. In another hour it was having seizures. At that point, I euthanized it.
It hits me hard when I lose a chicken in this way, especially a little chick. I went on a quest to discover how it had been exposed to a neurotoxin after I had ruled out injury that may have caused brain damage and ruled out toxic plants and poisonous insects. I hadn't used insecticides in years.
It took me several hours of wandering around the yard where I'd last seen the broody with her two chicks free ranging earlier. Finally, I all but tripped over the villain - my log splitter.
Machines such as this log splitter leak petroleum distillates, a substance as deadly to all living things as insecticides. They leak because running them causes severe vibration, so tightening fittings is a lost cause. The fluids leak onto the soil underneath, contaminating the grit that chickens eat for their digestion. My little chick wandered under the splitter and randomly selected a few pieces of grit from the contaminated soil. It only took one or two tiny particles and its fate was sealed.
I cleaned up the contaminated soil, placed a drip pan under the leaky fitting, and then secured some steel field fencing around the entire machine, closing off access to any small chicks, including adult chickens.
I'm hoping my loss and heartache can serve as your warning. You might want to identify these machines parked around the area where your chickens free range and either move them or fence them off.