The likely cause of a house fire that claimed the life a local veterinarian Wednesday is a heat lamp that was being used to keep a box of baby chickens warm inside her house, according to a state official. Melissa Watership, 46, had just obtained the chicks that morning and had put them in a sawdust-filled box in her bedroom, where the fire started, Maine Department of Public Safety spokesman Stephen McCausland indicated in a prepared statement released Friday afternoon.