Conservation and Management

Effects Of Human Activity

Collisions With Structures

Rarely reported hitting human-made structures; about 25 found at communication towers and lighthouses over many years.

Pesticides

Spraying of insecticides implicated in disappearance of A. m. nigrescens from Merritt I., FL, but no data (Sykes 1980). Because the watersheds occupied by A.m. mirabilis are downstream from agriculture, pesticides are a potential threat to that subspecies (Werner 1975).

Degradation Of Habitat

In the next century, a predicted sea-level rise of 2-4+ mm/yr, accompanied by increased storm frequency, would accelerate loss of tidal marshes. The effect would be most severe in the Northeast, where sediment delivery rates are lower than in Southeast (Shriver and Gibbs 2004, Erwin et al 2006).

Main man-made threat is habitat loss through filling, draining, diking, and pollution. By 1938, about 90% of salt marshes from Virginia to Maine were ditched to various degrees (Greenlaw 1992). Wetland loss in U.S. coastal zone has accelerated about 0.5% annually since the mid-1950s.Tidal wetland loss greatest in Florida, Louisiana, New Jersey, and Texas.

In many areas of Northeast, Seaside Sparrow numbers have been reduced because of drying of marshes by mosquito-ditching (Austin 1983, Greenlaw 1992). Ditching eliminates preferred foraging patches ( S. alterniflora, associated mud pools and mudflats), which are replaced by woody species (Iva and Baccharis) and reed (Phragmites), which have relatively low feeding value (Merriam 1983). In the Northeast in particular, Phragmites has expanded its range in response to lowering of water levels, replacing salt meadow grasses and degrading breeding habitats (Paxton et al 2007). Lowering of water levels and invasion of bushes along ditch banks increase access to predators.

In Everglades, Florida, flood patterns have been altered since 1946. The decline of A.m. mirabilis in e. Everglades is related to drying and increased incidence and severity of fires. In contrast, the decline of mirabilis in the western part of its range may be related to abnormally high water levels in the breeding season (Curnutt et al. 1998).

On the Gulf coast, Seaside Sparrows are more abundant in natural tidal marshes than in impounded marshes. Natural marsh vegetation consists of a low (< 1 m), interwoven canopy of Spartina, providing protection from predators; impounded marsh surfaces are usually inundated, thus reducing feeding opportunities (Gabrey et al 2001). Marsh impoundment is believed to have led to the disappearance of the Dusky Seaside Sparrow from Merritt I., FL (Sykes 1980, Walters 1992).

Historically, fires caused by lightning have probably benefited some populations. Periodic but infrequent fires, mimicking historic fire regimes, are beneficial if the timing and extent of burns are tailored to specific localities and habitats (Mitchell et al.2006). In Louisiana, numbers of breeding Seaside Sparrows decreased by 62% in the first year after a winter burn; in the second breeding season post-burn, the population was about 3X larger than it was pre-burn. Gabrey and Afton (2004) hypothesized that the initial population decrease was related to destruction of dead vegetation; sparrow numbers rebounded when sufficient cover became available. In subsequent breeding seasons, Gabrey and Afton (2000) recaptured birds they had banded in unburned marshes, but failed to recapture birds that had been similarly treated in pre-burned marshes. The authors suggested that the fire-displaced sparrows moved to lesser quality habitats; higher population densities in such habitats affected pair bonds and delayed territory establishment and nesting activities.

In Louisiana, wintering Seaside Sparrows were absent immediately after burns, but present in unburned marshes; sparrows reoccupied the burned marshes in second winter after the burn (Gabrey et al. 1999).

Human/Research Impacts

Under controlled conditions, human visitation to nests does not appear to affect reproductive success (Post 1981a). During the era of egg-collecting, the A. m. nigrescens population on Merritt I., FL, may have been reduced by egg collectors. Single A. m. nigrescens eggs brought US$ 20.00 (compared to US$ 0.25 for A. m. maritimus egg; Barnes 1922). D. J. Nicholson and W. H. Nicholson alone collected at least 65 clutches (L. Kiff, S. A. Miller, pers. comm.).

Moderate grazing (1 animal unit/2.5 a) does not appear to be detrimental; winter burning to improve cattle range, when done in small blocks and in mosaic pattern, is acceptable (Holder et al. 1980, Mitchell et al. 2006).

Management

Conservation Status

The Office of Migratory Bird Management considered Seaside Sparrow a migratory non-game bird of management concern (U.S. Fish and Wildlife Serv. 1987). Vulnerability of species varies widely in different regions. Several states classify species, or some of its races, in highest 2 classes of vulnerability. Most coastal states have enacted laws to protect estuarine wetlands; these vary markedly in extent of protection provided (Greenlaw 1992).

This sparrow is adaptable enough to persist in small groups in remnant marshes, but small populations are prone to stochastic extinction. Local losses are cumulative until regional extirpation occurs. This stage has been reached along the Atlantic Coast of Florida (Kale 1983).

Listed as a Federally Endangered species, A. m. nigrescens received considerable attention from state and federal governments, including purchase of 1,820-ha tract to preserve the population on the St. Johns River, FL (Baker 1978). After the American Ornithologists’ Union (1973) reclassified nigrescens as subspecies, federal agencies were unable to continue the recovery effort (Walters 1992). By 1980, only 6 individuals, all males, remained. In order to preserve the genes of this subspecies, biologists captured 5 of the males. One male mated with a captive Scott’s Seaside Sparrow (A. m. peninsulae), and produced 3 fledglings. It was later determined, through brother-sister matings, that first generation hybrids were fertile (Webber and Post 1983).

Measures Proposed

Habitat protection alone may not be sufficient to stem local extinctions. In some cases, management intervention may be necessary. Object of intervention should be creation of mosaic of nesting and feeding sites (poorly drained areas where medium-height cordgrass grows). Managers of altered marshes could block selected ditches to create favorable conditions. On high (supratidal) marshes, shallow pools constructed near spoil islands with nesting substrate (wood vegetation such as Iva) may encourage sparrows to settle.

Most researchers agree on the efficacy of fire as a management tool, although they differ on the details of application. Gabrey and Afton’s (2004) findings are similar to those of Werner (1975): sparrows decrease immediately after a burn, increase 3-4 yr post-burn, but abandon the site after 6 yr. Optimum sparrow habitat might be maintained by burns every 3-4 yr. Curnutt et al (1998), however, found that some populations did not abandon burned areas immediately, but due to the patchy nature of natural fires in Everglades, were able remain on their home ranges after a fire., Latter authors suggested that sparrows will occupy sites that had burned 10-12 yr previously, but numbers were highest where there had been 1-2 fires during previous 10 yr. Taylor (1983), however, posited that A.m. mirabilis numbers do not decline until 8-10 yr post- burning, stating that severity and thus effect of fire on vegetation, was related to soil depth. Burned sites with soil depths > 20 cm had more rapid recovery, and birds recolonized more rapidly. In shallow-soil areas, sparrow densities remained low for up to 10 yr, and densities were lowest after dry-season burns.

Techniques for breeding and rearing sparrows in captivity (Post and Antonio 1981) and for preserving sperm (Gee and Sexton 1983) developed during recovery effort for A. m. nigrescens may be applicable to other populations.