Help!! my neighbours chicken just died!?

I have been looking after my neighbours 4 chickens for over a fortnight now ... and i have been doing everything they told me to do. I went out to feed them today and to my surprise only 3 came out when i opened the hatch. Normally they are rushing for food. I went to check where the 4th was i looked in the hutch and it was lying there dead. I dont know what to do! they are not back untill the 4th of october and it is the 23 of september. Help Please!!