Here are my tips for finding target birds in the heat haze:
1) Scout for the birds at the time of day you'll be looking for them. It won't do you any good to know where a Yellow-throated Warbler has a territory if he only sings in the mornings.
2) Learn the birds call notes! They often won't be singing, but some creative pishing/screech owling can often get a bird to call in alarm. This works particularly well with Kentucky and Prothonotory Warblers and is often how we get them.
3) If possible, try to find an actual nest. It takes a LOT of scouting, but sometimes you get lucky and it saves you some time.
4) Find as many possible territories for the target birds right along our route as possible. Sometimes you have to visit multiple spots until you hear or see the bird. I often have 5-6 Kentucky spots and up to 15 Prothonotory spots lined up along our route and it can be scary how many we stop at before we get our quarry. It only takes a minute to make a quick check at each spot as long as it's along the way.
5) Keep your eyes open too! It's easy to get so keyed in on listening that you forget to look for the birds. We spend a lot of time in Blue Grosbeak habitat and probably see them as often as we hear them.
6) Look for birds on territory that are unpaired or have lots of established neighbors close by. These birds are the most likely to be singing at any time of day because they're still trying to attract a mate or carve out a territory (ie: desperate!). If you spend a lot of time scouting you'll see patterns to when birds sing and learn to pick out these individuals. It's particularly valuable for Summer Tanager which can be spread out pretty thin. Birds that have already attracted a mate and are starting their nest cycle are the least likely to bother with singing.
7) Make a mental note of every spot where you find your target birds. you never know which ones will decide to sing the afternoon of "game day". Sometimes a spot where you hadn't had that bird for over a week will for some reason hold an individual in full song that afternoon?! I'll take it, and it happens.