Cape Sable Seaside Sparrow

Ammodramus maritimus mirabilis

Description

The Cape Sable seaside sparrow, Ammodramus maritimus mirabilis, is a medium-sized sparrow restricted to a small region of the southern Florida peninsula. They are non-migratory residents of fresh water to brackish marshes. The Cape Sable seaside sparrow has the distinction of being the last new bird species described in the continental United States prior to its reclassification to subspecies status. The restricted range of the Cape Sable seaside sparrow, and the changes in habitat that have occurred as a result of changes in the distribution, timing, and quantity of water flows in South Florida, have led to its listing and continue to threaten the subspecies with extinction.

The Cape Sable seaside sparrow is a medium-sized sparrow 5.1-5.5 in (13-14 cm) in length. Of all the seaside sparrows, it is the lightest in color. The dorsal surface is dark olive-grey and the tail and wings are olive-brown. Adult birds are light grey to white ventrally, with dark olive grey streaks on the breast and sides. The throat is white with a dark olive-grey or black whisker on each side. Above the whisker is a white line along the lower jaw. A grey ear patch outlined by a dark line sits behind each eye. The lores of the head are yellow. The leading edge of each wing has a small yellow patch near the alula. The legs and bill are grey. There are no noticeable differences in markings between the sexes. However, there are significant differences in the sizes of specific body parts between the sexes. Young birds differ from adults in that they do not have whisker marks, lack the yellow lores, and have brown streaking on the back.

Behavior

The Cape Sable seaside sparrow is a non-migratory subspecies. As with many other seaside or savannah sparrows, males occupy and defend their territories during the breeding season. Cape Sable seaside sparrows defend territories centered around their nest sites that are smaller than their home ranges, but may include foraging habitat. Breeding activity by males, particularly singing behavior, appears to decrease with increased surface-water conditions. Singing declines if water levels rise above approximately 3.9 in (10 cm).

The primary song of Cape Sable seaside sparrows is sung by males, and is composed of clicks and trills. The head bobs up and down during the introductory clicks and then tilts slightly up and back as the song is completed with a buzzy trill. The primary song is normally sung from a conspicuous perch and functions to both mark territories and attract mates. The song lasts approximately 1.5 seconds and may be repeated 10-13 times per minute. Singing by males occurs most often during early morning and late afternoon and evening, with unmated males singing the most persistently. As the temperature rises over the course of the day, the time spent singing decreases.

Nesting occurs from late February through early August. The majority of nesting occurs in the spring when marl prairies are dry. Cape Sable seaside sparrows usually raise two broods in a season, although they may raise a third brood if weather conditions allow. Sparrows build new nests for each successive brood. Nest cups are placed approximately 5.5 in (14 cm) above the ground and are constructed with grasses. Sparrows construct their nests with materials that are locally common and sometimes place taller grasses over the nest cup to conceal the nest. Nests are placed in clumps of grasses composed primarily of muhlenbergia and spartina. A typical nest is constructed using sawgrass as the base, and finer grasses for the lining. Most nests are constructed with dead material although one nest observed during the 1997 breeding season was constructed with some live material. Nesting may not be initiated if water levels are at a depth greater than 3.9 in (10 cm) during the breeding season. The end of the breeding season appears to be triggered by the onset of the summer rains. When water levels rise above the mean height of the nests off the ground, sparrows cease breeding.

Cape Sable seaside sparrows often retained the same mate for successive nest cycles but that some individuals changed mates after one nest cycle. Additionally, some males failed to pair during the entire breeding season. Interactions between male and female Cape Sable seaside sparrows include chasing behavior, food begging by the female, males carrying food to the female, and males carrying nest behavior while softly singing. Males chase females as often as they chase males. Often, females have difficulty flying any distance without being chased by a male into the grass.

Cape Sable seaside sparrows lay three to four eggs in each clutch. Incubation has been estimated to take 12-13 days. The young spend nine to 11 days at the nest. Both parents rear and feed the young birds and may do so for an additional 10-20 days after the young fledge. Fledglings often occur in groups of two to seven and are occasionally alone. They are incapable of flight until they are approximately 17 days of age; when approached, flightless fledglings will freeze on a perch until the threat is less than 3.3 ft (1 m) away, and then run along the ground.

There are conflicting data on the reproductive potential of the Cape Sable seaside sparrow. However, the population has the ability to maintain or expand due to the 90% survival rate of males and the potential to produce two clutches of four eggs each breeding season.

Cape Sable seaside sparrows typically forage by gleaning items from low vegetation or from the substrate. The Cape Sable seaside sparrow is a dietary specialist. They commonly feed on soft-bodied insects such as grasshoppers, spiders, moths, caterpillars, beetles, dragonflies, wasps, marine worms, shrimp, grass, and sedge seeds. Significant differences were detected in nestling diet between years and sites, which reflects the patchy distribution of insects and opportunistic nature of the sparrow. The sparrow appears to shift the importance of prey items in its diet in response to their availability.

The Cape Sable seaside sparrow is non-migratory. The fidelity of breeding male sparrows to their territories is high; many male seaside sparrows will defend the same area for two to three years. During the non-breeding season they appear to congregate, and fly short distances within their range. Cape Sable seaside sparrows have never been observed outside of muhlenbergia prairies during the wet-season. Preliminary results of a wintering ecology study report that resighted banded adults during the 1996-1997 wet season moved short distances from the sites they were banded in 1995 and 1996. Lockwood also reported that at the end of the breeding season, sparrows move into denser vegetation and become secretive. Preliminary data suggest that they are most often found in sawgrass sways and smaller hammocks within the breeding range.

Habitat

In the 1930s, Cape Sable was the only known breeding range for the sparrow; areas on Cape Sable that were occupied by Cape Sable seaside sparrows in the 1930s have experienced a shift in vegetative communities from fresh water vegetation to mangroves, bare mud flats, and salt-tolerant forbs such as Batis maritima and Borrichia frutescens. The Hurricane of 1935 is believed to have resulted in the succession of the plant community on Cape Sable from one dominated by fresh water plants to one dominated by salt tolerant plants; as a result, Cape Sable seaside sparrows no longer use this area.

The preferred nesting habitat of Cape Sable seaside sparrows appears to be a marl prairie community that is dominated by muhly grass. These short-hydroperiod prairies contain moderately-dense, clumped grasses, with open space permitting ground movements by the sparrows. Sparrows tend to avoid tall, dense, sawgrass-dominated communities, coastal spike-rush marshes, extensive cattail monocultures, long-hydroperiod wetlands with tall, dense vegetative cover, and sites supporting woody vegetation. Cape Sable seaside sparrows avoid sites with permanent water cover.

Studies completed since the 1970s document that muhly prairies are the preferred habitat of the Cape Sable seaside sparrow and support the highest densities of sparrows. For example, in the 1970s and 1980s, the largest populations of Cape Sable seaside sparrows were supported by muhly prairies. The suitability of this vegetative community for the sparrow is driven by a combination of hydroperiod and periodic fires. Fires prevent hardwood species from invading these communities and prevent the accretion of dead plant material, both of which decrease the suitability of these habitats for Cape Sable seaside sparrows. In the Taylor Slough area, sparrow numbers increased annually in areas that had been burned up to three years previously. Four years after a fire, he expected the suitability of these habitats to decline sharply. Recent analyses suggest that this is a localized response to fire and that, typically, sparrow numbers increase up to 10 years post-fire. The response of the sparrow population following fire is dependant on the rate of vegetation recovery, the soil depth, and the amount of exposed pinnacle rock. At sites where soil depth is 15.7 in (40 cm) or greater, or on soils without pinnacle rock, vegetation recovery is rapid and the birds recovered more quickly following fire. At sites where soil depths are less than 7.9 in (20 cm), and where considerable pinnacle rock occurs, the birds begin to reoccupy sites four years post fire.

Little is known about the wintering habitat of Cape Sable seaside sparrows. Birds have been observed near tree islands in December but may additionally be wintering within the salt marshes of the southern Everglades. Because the birds are secretive by nature, radio telemetry will be necessary to determine wintering habitat.

Distribution

Seaside sparrows are members of the family Fringillidae. There are nine recognized subspecies. Two of the subspecies, the Cape Sable seaside sparrow and the recently extinct dusky seaside sparrow (Ammodramus maritimus nigrescens ), occurred in isolated and restricted ranges. The eight surviving subspecies of seaside sparrow are distributed along the east coast of the United States, from Massachusetts to southern Florida, and along the Gulf coast, from southeast Texas to the west coast of Florida. Cape Sable seaside sparrows have the most restricted range of any of the seaside sparrows, and occur only in the Everglades region of Dade and Monroe Counties in South Florida. They are non-migratory and are isolated from other breeding populations of seaside sparrows. The Scott's seaside sparrow, which is the closest in locality to the Cape Sable seaside sparrow, is located approximately 186 mi (300 km) to the north.

The original range most likely included all suitable habitat in South and southwestern Florida, and extended from Cape Sable (south) to Ochopee (northwest), and east to Taylor Slough and the east Everglades. Presently, the known distribution of the sparrow is restricted to two areas on the east and west sides of Shark River Slough, and Taylor Slough.

Threats

The plight of the dusky seaside sparrow is an important lesson to be learned from and should be considered when developing recovery objectives for the Cape Sable seaside sparrow. The dusky seaside sparrow, like the Cape Sable seaside sparrow, was a victim of our manipulation of the natural hydrologic regime. One of the reasons the recovery plan for the dusky seaside sparrow failed was because it failed to recognize how critical the changes in the natural hydrological regime were to the bird. The recovery plan failed to incorporate the history of water management and the linkage of the U. S. Army Corps of Engineer's Upper Basin Diversion Project to the plight of the dusky. The Upper Basin project narrowed the flood plain of the St. John's River from approximately 20 mi (32.2 km) to barely 2 mi (3.2 km) wide, and citrus and pasture replaced the native landscape.

These problems have a familiar ring when contemplating recovery for the Cape Sable seaside sparrow. In the case of the dusky, none of the recovery objectives were met. We need to be certain that we react differently for the Cape Sable seaside sparrow or we will suffer similar consequences. As of today, the majority of the recovery objectives identified in the Cape Sable seaside sparrow recovery plan in 1983 remain unaccomplished, and population numbers are declining. Flood control for agriculture and urban dwellings has taken precedence over reestablishing more natural hydropatterns in Cape Sable seaside sparrow habitat. The Cape Sable seaside sparrow evolved in a variable environment. This variability allowed an abundance of organisms with different habitat needs to co-exist. For example, the endangered snail kite requires areas of deep water that support apple snails for optimal foraging habitat; the endangered wood stork, requires water levels to drop to concentrate fish during the breeding season. These conditions differ from those breeding conditions required by the Cape Sable seaside sparrow who, as stated above, require less than 3.9 in (10 cm) of surface water to nest successfully; yet these species evolved to co-exist in the Everglades system and could do so because of the large spatial extent and diverse environmental conditions available in the South Florida landscape. If we manage the system to mimic the conditions that historically existed, the needs of the Cape Sable seaside sparrow should not conflict with other native Everglades species.

Historically, the Cape Sable seaside sparrow was found in freshwater and brackish water marshes from Carnestown to the marl prairies adjacent to Shark River and Taylor Sloughs, including the Cape Sable area. This area periodically experiences extensive flooding, fires, and hurricanes which may result in shifts in habitat suitability for the Cape Sable seaside sparrow by changing vegetative composition and structure. Cape Sable seaside sparrows probably adapted to this natural disturbance by varying their distribution within their range as habitat suitability changed.

Cape Sable seaside sparrows were first documented in the Big Cypress basin in 1928 and appeared to flourish there in the 1950s, but were extirpated as a result of widespread frequent fires by the early 1960s. Today, there is uncertainty with regard to the relationship between Cape Sable seaside sparrow habitat use and fire.

Since the 1970s, the Taylor Slough area had been relatively important to Cape Sable seaside sparrows. However, the extent of suitable habitat in the Taylor Slough area is decreasing due to invasion by exotic trees and shrubby vegetation. The limited distribution and habitat specificity of the Cape Sable seaside sparrow make it vulnerable to catastrophic or extreme events. The small total population size and small number of subpopulations also jeopardizes the survival and recovery of the Cape Sable seaside sparrow. If the population size becomes too small to allow birds to recolonize areas that have been locally extirpated, the species will become much more prone to extinction. Competition and predation also threaten the Cape Sable seaside sparrow. Raccoons and rice rats may be the chief predators. Predation by feral cats and dogs, anthropogenic fires, and human land exploitation could have caused the population declines of the sparrow in the Ochopee region.

Conservation and Recovery

South Florida's ecosystems have been severely degraded by the Central and Southern Florida Project which encompasses 17,992.3 sq mi (46,600 sq km) from Orlando to Florida Bay, and includes about 994.2 mi (1,600 km) each of canals and levees, 150 water control structures, and 16 major pump stations. This system has disrupted the natural volume, timing, quality and flow of surface and ground water throughout the Everglades. In recognition of the detrimental affects that this flood control system has had on the ecosystems in South Florida, numerous hydrologic projects, whose purposes are to aid in the restoration of South Florida's ecosystems while maintaining flood control, are in various stages of planning and implementation. These hydrologic restoration projects will provide some of the tools necessary to restore habitat critical to the recovery of the Cape Sable seaside sparrow.

The survival and recovery of the Cape Sable seaside sparrow depends on the restoration of hydropatterns throughout its range, including the redistribution of flows across all of Shark River Slough. This effort will require increasing flows into northeast Shark River Slough and decreasing flows into the area west of Shark River Slough. The U.S. Fish and Wildlife Service believes alternative strategies must be devised to reduce the impacts to Cape Sable seaside sparrows associated with present-day structures and operational schedules, including those associated with flood control. For example, interim measures should include actions that reduce the adverse effects of regulatory releases on Cape Sable habitat and result in conditions that more closely mimic those of the historical system. During periods of drought, rainfall delivery formulas which result in more natural water patterns should be implemented. Vegetative communities within the range of the sparrow have been disturbed as a result of these changes in water patterns, which may be restored with redirected water patterns. Limited information is available about the relationship of the Cape Sable seaside sparrow to fire. Sparrows reoccupy sites with shallow soil approximately four years after a burn, but populations may remain at low densities for up to 10 years. On deeper soils or on soils without pinnacle rock, birds are present the second breeding season after a burn and increase in numbers through the fourth year. Studies need to be implemented to determine whether managed burns are necessary to sustain healthy muhly prairie communities. The original designation of critical habitat was inadequate to cover the full range of the Cape Sable seaside sparrow. When re-designating critical habitat for the Cape Sable seaside sparrow, it will be important to include all potential habitat, including areas not recently utilized by the birds. This will help to incorporate the dynamic nature of the bird and the natural variability associated with the Everglades ecosystem. Because the Everglades is a system that evolved with inherent natural variability, native Everglades species developed traits that have allowed them to respond to varying conditions. In the case of Cape Sable seaside sparrows, birds disappear and reappear from known habitat over time, most likely in response to localized breeding conditions. By incorporating all potential habitat, those areas that may be utilized by Cape Sable seaside sparrows over the long-term will be protected. Most importantly, when re-designating critical habitat, constituent elements must be defined. The primary constituent element for the Cape Sable seaside sparrow should be the maintenance of a hydroperiod that maintains the preferred vegetative communities for successful breeding. During the breeding season, surface water levels should be at or slightly below the surface within the short-hydroperiod prairies, and should be achieved through adherence to a rainfall-driven operational schedule. Adherence to such a regulation schedule will promulgate the restoration of hydropatterns that best support Cape Sable seaside sparrows, in addition to other native Everglades species. Other constituent elements should include necessary vegetative structure, as maintained through appropriate fire management plans, an exotic control program, and a muhly prairie restoration program.

Contact

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

References

Quay, T.L., and E. Potter, eds. 1983. The Seaside Sparrow: Its Biology and Management. Occasional Papers of the North Carolina Biological Survey, North Carolina State Museum.

U.S. Fish and Wildlife Service. 1983. "Cape Sable Seaside Sparrow Recovery Plan." U.S. Fish and Wildlife Service, Atlanta.

Werner, H.W. 1975. "The Biology of the Cape Sable Sparrow." Report. U.S. Fish and Wildlife Service. Everglades National Park, Homestead, Florida.