The present and future of the Cape Sable seaside sparrow

Post, William; Greenlaw, Jon

The purpose of this paper is to review the biology of the Cape Sable Seaside, and to discuss its management in light of what, is known about the species as a whole. Seaside Sparrows (Ammodramus maritimus) breeding in the Everglades region belong to a morphologically distinct subspecies (the Cape Sable Seaside Sparrow, A. m. mirabilis). This population is isolated from the other races of the Seaside Sparrow, the closest of which, the Scott’s Seaside Sparrow (A. m. peninsulae), is found 300 km north. Other than appearance, the only significant difference between the Everglades subspecies and its relatives is in habitat use. Unlike other Seaside Sparrows, most of which live in salt marshes, the Cape Sable Seaside Sparrow now appears to be confined to freshwater sites. The history of the Cape Sable Seaside Sparrow is fragmentary. Populations have frequently disappeared, and the same or other populations have been rediscovered in widely separated areas, often many years later. These long-range shifts in distribution, if real, appear to have been in response to the fluctuations that characterize the temporally unpredictable environment of the Everglades. Disturbances such as fire and hurricanes have caused shifts in population distributions, and also long-term modifications of sparrow habitats. Since the research of Harold Werner, initiated in 1970, several studies have been conducted in an attempt to determine the number of sparrows remaining, and to gather information about their demography. Werner estimated that 2,000-3,000 birds remained in 1974-1975. In 1981 the population was again surveyed, and it was estimated that 3,300 male sparrows remained. In 1991 the survey was resumed. Although referred to as the “extensive” survey, it has not completely covered all potential habitats of the species, nor even the original 1981 census points. Data collected from a limited number of birds indicate that the Cape Sable Seaside Sparrow has high reproductive potential: females can produce up to nine fledglings per year. Survival rates are high: on average, at least 60% of adults survive from year to year. Preliminary radiotelemetry studies indicate that juvenile sparrows can disperse long distances from their natal sites. Based on the results of the extensive surveys, claims have been made that the subspecies is decreasing. These results do not fit a population model that incorporates high fecundity and survivorship, as well as extensive juvenile dispersal. This contradiction may be clarified when valid survey data are available, and after more detailed demographic information has been gathered. The main Cape Sable Seaside Sparrow population now appears to live in muhly (Muhlenbergii filipes) prairie east of Shark River Slough. Although the recovery plan states that muhly prairie is the “preferred” habitat of the subspecies, information about nesting habitats that the birds have used in the past suggests that muhly prairie is simply the habitat into which the sparrow has moved most recently. Management decisions to enhance the recovery of the Cape Sable subspecies are based on the results of the extensive surveys, and on the corollary assumption that muhly is the optimum habitat for the subspecies. For the most part, recovery efforts since 1975 have focused on controlling one environmental factor (water level) that affects sparrow distribution in this one habitat type. If the prediction of the government research, that the subspecies may become extinct within 20 years is true, then immediate intervention is warranted. Strategies such as relocation, captive-rearing, localized flood control, and predator control are recommended. Federal agencies responsible for the recovery of the sparrow have been unwilling to take such actions in its behalf.

The present and future of the Cape Sable seaside sparrow

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