Transpiration and evaporation
Because the mother had red her it means the woman is heterozygous and the man is homozygous recessive so there is a 50% chance of having a child with red hair and a 50% chance of having a child with black hair.
Some abiotic factors that can limit a population are space and weather these are called limiting factors (and how much water is provided)
If want a direct answer it would be the decrease in mice, but if you want to get technical the decrease in grain spills caused mice to leave so that would be the indirect cause