During summer, in many coastal New England marshes, there reside secretive sparrows once thought to be of a single species known as the Sharp-tailed Sparrow. Genetic research led to the species being split into Nelson's Sharp-tailed Sparrow and Saltmarsh Sharp-tailed Sparrow. Since then, the "Sharp-tailed" portion of the names has been dropped, much to the dismay of those who adore tongue twisters. (I challenge you to say "Saltmarsh Sharp-tailed Sparrow" 5 times fast!)
Nelson's Sparrows breed along the east coast from southern Maine into parts of Canada, as well as in some interior portions of the continent. Only in southern Maine does the species share breeding grounds with the more southerly, and strictly coastal, Saltmarsh Sparrow, and it is primarily in this overlap zone where the two species are known to hybridize.
Nelson's Sparrows (at least typical individuals who breed along the Atlantic) have a yellow-tinged chest with blurry streaks and a bluish bill (vs. Saltmarsh Sparrows who have more distinct streaks on a whiter chest and a yellow bill). That said, there is some overlap, and hybrids (especially in southern Maine) may show a blend of field marks that make species determination impossible.
Visit a Maine saltmarsh on a June or July day and listen for the Nelson's song, which has been described as sounding like a water droplet hitting a hot frying pan. Here's a sample of a bird from the Scarborough Marsh, recorded by Tayler Brooks:
If you're persistent, observant, or just plain lucky, you'll be able to spot the singer on a marsh perch as I was able to do to capture these photos. To view the following images in full-size, click here.