My healthy 3 month old chicken just got very tame, lethargic, fluffed up and then died suddenly in a 24 hour period. I only noticed symptoms for an hour before she died. I am so worried that whatever caused this might lead to more deaths in the flock. I am new at this and have come up with a few possibilities: 1. Weed killer and lawn fertilizer applied to lawn (where chickens graze) in June and Sept respectively. We've had a heavy rain and a lot of sprinkler use since then. 2. Hydrangea and jasmine accessible to birds about 30 min/day. 3. Didn't wash water and food containers with soap/hot water for a few weeks. Just scrubbed well with cold water. 4. They are sleeping in a coop with 100 watt infared bulb with outside temps at 35-40 at night. I leave the window open about 2 inches for ventilation. (4x4' coop with 6 hens) Could any of these have caused her death? Anything I should do for the other chickens to keep them safe? Any advice from the veterans out there would be great. Thank you!