I put them back in their pen just before 6 and by 8 pm one was already stiffening. I suspect diazinon poisoning. I had sprinkled some around the base of the house last week to kill ants. Since then we've had rain but apparently some of the crystals had not washed into the dirt. The birds had foraged under the hollyhocks next to the chimney, when I checked the area, there were still piles of diazinon on some of the dead leaves. If I had raked the area in the spring, this wouldn't have happened. If I'd checked to be sure the diazinon was all absorbed this wouldn't have happened. If I'd waited another week to let the chickens out.... etc, etc.
One of the chickens isn't doing well either. He's listless and breathing fairly hard. I've tried a purgative of molasses water, all I can do is cross my fingers and wait, and hope some of them will survive.
What a lousy way to end the day.