my chickens have an expected life span of about 7 years - could it be old age?  I don't see that the hot weather would do it unless they are in confined conditions and ran out of water.  I have one of those dripping water feeders - it gets dirty in the trough in five seconds.  I also put a bowl of water out in the back yard, they do like to drink a lot and cluster round for a drink of fresh clean water.  I realised that the carpet snake having a nap in my chicken coop had followed a pair of large, maybe marsupial rats in there and eaten one of them the other was there at the feeder the next day.  It was a very attractive little furry animal.  So that's why I'm thinking marsupial, I haven't seen it since.  I don't have any other rats that I know of.  I keep my feed in the house.  Other people use galvanised steel bins.  I had some bits of star picket so I put that round the bottom of the coop to keep the rats out - not that that stopped the chickens scratching out some new holes.  But no further sightings of rats or mice.  Yes chickens are a surprisingly friendly and engaging bunch aren't they.