Carolina Chickadees got me my year Blue-gray Gnatcatcher, Blue-headed Vireo, and Black-and-white Warbler – and that was only today!
Forest birds are distributed patchily across the landscape, and particularly when dealing with migrants, you often travel through extensive BFZ's (Bird Free Zones) between patches with birds. Paying special attention when chickadees are around helps narrow the search. Black-capped, Carolina and Chestnut-backed Chickadees are catalysts for mixed-species foraging flocks, and during migration birders can hardly do better than hang out with them. [This seems less true with Boreal Chickadee, and I lack sufficient experience to know whether migrants glom onto Mountain Chickadees. Reader insights are welcome!] My oft-voiced rule while leading field trips at migration hotspots like Higbee Beach is to "never walk away from a chickadee."
Never drive past one, either. This spring migration I'm confined to my truck thanks to recent knee surgery. Trying to find arriving migrant woodland birds by vehicle in an extensive, somewhat uniform landscape like Cape May's Belleplain State Forestis a bit daunting, because you can't hear or see nearly as well from inside I car, and there's too much habitat to cover to just stop anywhere.
Luckily, chickadees are vocal. Driving around Belleplain, whenever I hear a Carolina Chickadee, I pull off and kill the engine. After listening passively for a bit, I try some pishing, right from the car (this can work great, with the car working as a blind). Often a migrant associating with the chickadee flock will come in silently or sing in response to pishing, and if your pishing gets the chickadee flock riled up, their antics will virtually always bring the migrants for a look. Today's Blue-headed Vireo never made a sound but came right in, the Black-and-white sang of its own volition after a period of passive listening, and the gnatcatcher, being a gnatcatcher, immediately responded to my pishing and proceeded to mob my truck. None of these birds were in spots that looked different enough to stop "just because," but the word of a chickadee is good with me.