Effects of Human Activity
Collisions with Structures
Pesticides and Other Toxic Chemicals
Tidal marsh sparrows on Atlantic coast are subject to greater mercury (Hg) exposure on breeding than on overwintering grounds (207). Saltmarsh Sparrows bioaccumulate Hg (208) and individuals exhibit body loads averaging 0.7 ppm wet weight in summer and 0.4 ppm in winter (207). Lower loads in winter may depend on dietary shift to greater seed consumption in winter compared to invertebrate use in summer. Winder and Emslie (209) found higher concentrations in Saltmarsh Sparrow than other tidal marsh sparrows, though the reasons for this difference are unknown. Hg levels seen in a large proportion of Saltmarsh Sparrow are similar to those that can have physiological impacts on birds, potentially influencing reproductive success and survival, especially in areas of high contamination (210, 209). No evidence for effects on reproductive success detected, however, in study of 9 sites between New Jersey and Maine (K. Ruskin, unpublished data). No information on pesticides or other toxic chemicals.
Degradation of Habitat
Long-term marsh degradation and loss due to coastal development has presumably affected Saltmarsh Sparrows throughout their range for decades: New Jersey (91), New York (211, 140), Connecticut (76), Massachusetts (212). Coastal marsh area has declined by ~40% in the U.S. North Atlantic since the 1800s (213), and what remains has undergone widespread changes due to altered hydrology, introduced species, pollution, and increasingly sea-level rise. Not all changes have necessarily harmed the Saltmarsh Sparrow as efforts to drain marshes via ditching might have increased areas of Spartina patens meadows and reduced the risk of nest flooding.
Strong population declines since at least the 1990s suggest that recent changes have been detrimental (see Population Status: Trends). Causes of declines uncertain, but apparently linked to tidal restrictions on many marshes, which perhaps reduce sediment flow (74). No evidence for demographic differences between a ditched and an unditched marsh in New Jersey (46), nor for a link between ditching and recent population trends (74), but paucity of unditched sites makes comparisons difficult. Widespread vegetation changes and accretion data also suggest that marshes are getting wetter throughout large portions of the species range (214, 215), which in turn suggests an increased risk of tidal flooding during nesting.
No direct tests, but anecdotal observations suggest that activity around nests during nest building can cause abandonment (CSE, JSG). Telemetry studies have resulted in mortality due to antenna entanglement as birds move through dense marsh grasses and possible abandonment of fledglings with transmitters (216); subsequent field tests suggest that careful choice of antenna material can reduce entanglement problems (CSE).
Recent studies suggest that, under current conditions, there is a low chance of the Saltmarsh Sparrow persisting beyond the middle of this century. The current ~9% per annum decline across the species’ range (74) suggests a 75% population decline between 1998 and 2012. Analysis of vital rates at 21 study sites from Maine to southern New Jersey found that mean growth rates were negative at 17 sites, and that only one site had rates that would allow unambiguously positive growth (201). Two smaller-scale regional analyses also have been conducted. The first found a 95% chance of extinction in coastal Long Island Sound between 2032 and 2056 (188). The second predicted a high chance of near-term extinction at Forsythe National Wildlife Refuge, New Jersey (217). Given the consistency in population declines (74) and population growth rates (201), it is likely that these detailed local studies are representative of populations across the species range.
Even before recent trend and viability analyses were conducted, Saltmarsh Sparrow was listed as Vulnerable on the IUCN Red List (218). Re-evaluation in light of new data suggests species should be classified as Endangered based on a population decline of > 50% within 10 years with no sign that the decline has ceased (CSE, based on criteria in 219). Listed as a Red Watch List species by Partners in Flight (220); as a species of concern by state agencies in Maine, New Hampshire, Connecticut, New Jersey, Maryland, and Virginia; and as a species of Greatest Conservation Need in all states in which it breeds.
Severity of ongoing and projected declines has resulted in suggestion that listing under the U.S. Endangered Species Act may be warranted and a U.S. Fish and Wildlife Service species status assessment is in progress. Atlantic Coast Joint Venture has identified Saltmarsh Sparrow as a flagship species around which to focus conservation actions, and many partner states are developing plans to protect and enhance habitat. Rate of habitat change, however, is high (214, 215) and impediments to inland marsh movement is considerable due to both ecological (215) and human (221) constraints.
Management actions under consideration comprise long-term solutions focused on ensuring that coastal marshes persist in the face of future sea-level rise and short-term solutions designed to “buy time” while longer-term solutions are implemented. Potential long-term solutions include protection of upland areas that marshes can migrate into, clearing of forest and other manipulations in areas adjacent to marshes to facilitate and speed up the migration of marsh habitats, increasing sediment flow down rivers to enhance the ability of existing marshes to build elevation, and living shorelines to help trap sediment and protect marshes from erosion. Shorter-term solutions under consideration include the use of temporary tidal restrictions during the nesting season to reduce nest losses by dampening the most extreme high tides and sediment deposition to build elevation in existing marshes. Restoration activities to keep invasive Phragmites out of marshes are also important, but restoring tidal flow for this purpose has not resulted in improved habitat as the restored marshes tend to be dominated by low elevation marsh plants suggesting that flooding is too frequent for successful nesting (222).
More extreme solutions such as the creation of floating marsh islands and captive breeding also have been discussed; initial experimentation has been conducted on the former (e.g., B. Benvenuti, unpublished data). These options, however, likely to be useful only in worst-case scenarios. Most methods described above remain untested, although pilot investigations for several have begun (CSE). Conservation planning work has also been conducted to identify marsh patches that most birds use (W. Wiest, unpublished data) and most cost-effectively support current populations (B. Klingbeil, unpublished data), and to identify how this set of marshes will change under future sea-level rise scenarios (B. Klingbeil, unpublished data).