During periods of hot, humid weather, early morning is the only comfortable time of day to be outdoors. With afternoon highs near 100, even the hours near dusk remain unpleasantly warm and it takes several hours of darkness to cool the air into the 70s.
By middle age, most of us have outgrown the late night party life and go to bed early enough to rise at dawn. This offers a clear advantage during the summer months, allowing us to enjoy the best part of the day. Wildlife, never subject to hangovers and late night social events, always take advantage of the cool morning hours and those of us who venture out in the early morning are blessed with their company. Birdsong is almost spring-like during those first hours of the day and both nocturnal and diurnal creatures are usually active.
By mid morning, the heat is building, the birdsong is fading and most wild creatures are heading for cool dens or shaded retreats. While they will venture out again in the evening, their songs will be subdued and their movements less vigorous. Only insects thrive in the heat; the rest of us tend to wilt.