Those really hot days of summer can really drain your energy.  It is tempting to sit in an air-conditioned room rather than go outside to look at birds.  Nesting birds must provide for their young even on those hot days.  Insects are plentiful this time of year, so it's a good time to find protein-packed food to feed their offspring.  Most birds are most active during the cooler hours of the morning and then again in the evening.  During the hottest parts of the day, they take refuge in a shady spot and may be hard to see.  A few birds seem to thrive on the heat and persistently sing all day long.  Dickcissels sing their repetitive songs from the grasslands even in the afternoon heat.  Indigo Buntings are another species that never seems to mind the heat.  Vireos can also be persisitent singers no matter what the temperature.  Soaring birds like Turkey Vultures take advantage of thermals to search for carrion, which is just as active during the middle of the day as any other time!