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Editor's Note: Nelson's Sparrow, treated in this account as an inland race of A. caudacutus, is now recognized as a separate species (A. nelsoni). Future revisions of this account will treat the 2 species separately. In addition, revision will sort out the English names of A. caudactus, which is now recognized as the Saltmarsh Sparrow.
The Sharp-tailed Sparrow is a secretive and highly localized species largely restricted as a breeding bird to wet meadows, edges of freshwater marshes, and salt marshes in recently deglaciated regions of interior and Atlantic coastal North America. This species is composed of two distinct groups, a northern one that is widely distributed and occupies three disjunct geographic areas, and a southern one that occurs along the northeast Atlantic Coast where it is in limited contact with the northern group in Maine. Birds in the two groups differ genetically, and males sing different songs.
Across its range, this sparrow is non-territorial and promiscuous, and only females provide parental care. Males occupy large overlapping home ranges, and at least in southern populations, the mating relationship features forced copulations by males. Active males engaged in reproduction greatly outnumber fertilizable females. Adult survival of both sexes and breeding success in southern birds are comparable to values observed in marshland and grassland relatives that exhibit biparental care.
Breeding success in many saltmarsh populations seems limited by storms and especially “spring” (high) tides, which often flood nests. The most successful pairs in these populations are those that renest soon after the flood tides of the new moon; the short incubation and nestling periods of this species allow such pairs to fledge their young before the returning flood tides of the full moon.