Nelson's (Ammodramus nelsoni) and Saltmarsh (A. caudacutus) sparrows are sympatric breeders in tidal marshes of the southern Gulf of Maine. These sparrows hybridize, have different mating strategies, and males do not defend territories or provide parental care. We estimated and compared core area sizes, home range sizes, and habitat use between species and between males and females. We radio-marked 140 sparrows (63 Nelson's and 77 Saltmarsh sparrows) during three breeding seasons (1999–2001) at Scarborough Marsh, Maine, USA. Home ranges of male A. nelsoni were 2.3 times larger (± SE) (119.68 ± 19.43 ha) than those of male A. caudacutus (52.85 ± 8.68 ha). Home range sizes of female Nelson's and female Saltmarsh sparrows did not differ from each other (female Nelson's home range  =  43.58 ± 13.10 ha; female Saltmarsh home range  =  27.81 ± 6.3 ha). More than 40% of male and 18% of female home ranges had two discrete core areas and, in most instances, each core area corresponded to a separate lunar cycle. We suggest that differences in mating strategies, densities, and adaptation to nesting in tidal marshes explain the larger home range estimates for male Nelson's Sparrows. Female and male Nelson's Sparrows' home ranges had more Spartina alterniflora cover and female Saltmarsh Sparrows' home ranges had greater Juncus gerardii cover than random locations. Home ranges of female Saltmarsh Sparrows had less Spartina alterniflora cover and more Juncus gerardii cover than female Nelson's Sparrows. We did not detect any differences in vegetation variables between male Saltmarsh and male Nelson's sparrow home ranges.