Hi, our chicken has been lethargic with reduced eating and drinking, reduced droppings, stands away from the flock. For the past several days, we have separated her from the flock. Her tail had been down but it has perked up since being separated, warmed up and given vitamins. She still seems interested in eating, drinking, but in much smaller quantities and tires easily. Upon further inspection, I found what looks and feels like a hard, black tumor attached to the skin on her back. It's solidly attached to her and causes her discomfort when I touch it. Any suggestions for what this might be and how to treat it?