Does Connecticut Warbler return by late May? Is Connecticut Warbler rare?

Although Connecticut Warbler is not rare, its habit of being a stealthy, skulking, "shy" species results it in being heard more often than seen. In addition, it breeds in habitats that are often inaccessible to birders, including spruce-tamarack bogs and muskeg (as well as poplar woodlands and moist deciduous forests) in northern Minnesota, Wisconsin, Michigan, and central Canada. Individuals return as early as early May to, for example, southern Wisconsin, but it's been known to arrive as late as early June in irregular years. In general, as returning migrant, this species is considered a "late" arriving member of the wood-warbler family. Did you know this warbler was not described until Alexander Wilson did so in 1812? A nest for this species was not discovered until 1883, more than 70 years after Wilson's description. Even today, there are few to no rigorous, experimental studies of its general biology from the breeding or wintering ranges.