In order to successfully complete one brood, Cape Sable seaside sparrows need between 33 and 40 days when water levels do not rise above nest level. If there are less than 40 days where water levels do not drop below the nesting height then sparrows will be unable to breed during that season. If there are 60 days where the tussocks stay dry, the sparrow will be able to complete two broods. If there is greater than 90 days in the dry season, sparrows may be able to complete an additional third brood.
In the late 1970's there were a number of years where the water table was well below the surface. These years provided periods of greater than sixty days for the sparrow to breed. In the years between 1988 to 1992, the number of dry days for breeding was comparable to the late 1970's. The years 1994 and 1996 were some of the wettest on record. During these years most nests in the western sub-population were unsuccessful.