in the evening and all through the night , they would drift to the high ground for their night pasture and then work their way down low by the water and the two burr oaks by mid morning for the heat of the day , fighting off flies , standing nose to tail in the humid air and the shade before starting off their high ground migration again in the soft evening light , working their way slowly , grazing their way along the nice run of flat land by the stream before slowly climbing the hill .