The saltmarsh sparrow is a small bird that lives in coastal salt marshes along the Atlantic Coast of the United States. Over the past few decades, the saltmarsh sparrow population has declined dramatically, leading to its classification as a threatened or endangered species in many states. There are several key reasons why saltmarsh sparrows are endangered.
Habitat Loss
The biggest threat facing saltmarsh sparrows is loss of habitat. Saltmarshes are coastal wetlands that form in shallow bays and estuaries where sea water mixes with freshwater. Historically, there were over 2 million acres of saltmarsh habitat along the Atlantic Coast. Over the past 200 years, over 50% of historical saltmarsh habitat has been lost due to human activities.
The main causes of saltmarsh loss are:
- Draining and filling of marshes for coastal development
- Ditching and draining of marshes for mosquito control
- Reduced sediment deposition which leads to excessive marsh erosion
- Sea level rise due to climate change
As saltmarshes disappear, saltmarsh sparrows lose nesting and foraging habitat. Studies have found that saltmarsh sparrow density is directly correlated with marsh size and contiguity. Larger, unfragmented marshes support higher densities of breeding pairs. As marshes shrink and become fragmented, the sparrow population declines.
Nest Flooding
Saltmarsh sparrows nest very close to the ground in marsh grasses. This makes their nests highly vulnerable to flooding, which can be caused by normal tide cycles or storm surges. Research has found that flooding can destroy up to 90% of sparrow nests in a breeding season. Flooding may become an even bigger threat in the future as sea levels rise due to climate change.
Predation
Predators are another threat to nesting saltmarsh sparrows. Common predators in saltmarsh habitats include snakes, raccoons, marsh rice rats, gulls, and crabs. One study in Connecticut found that only 35% of monitored saltmarsh sparrow nests successfully fledged young, with most losses due to predation. Predation pressure may increase as habitat loss concentrates nesting birds into smaller areas.
Lack of Genetic Diversity
Saltmarsh sparrows have low genetic diversity across their entire range. This is likely because they have always had a relatively small global population and low dispersal rates between marshes. Low genetic diversity may make it harder for the species to adapt to habitat changes or new diseases and parasites.
Mercury Contamination
Saltmarsh sparrows may also be threatened by mercury contamination. Saltmarshes accumulate mercury pollution, converting inorganic mercury into highly toxic methylmercury. Saltmarsh sparrows are exposed to this methylmercury through their diet. Studies have found high mercury concentrations in sparrow blood and feathers, which could lead to reduced reproductive success and survival.
Population Estimates and Decline
In the early 2000s, the saltmarsh sparrow population was estimated at around 30,000 breeding pairs. However, surveys indicate the population has declined by over 75% since then. The current population estimate is around 6,000-9,000 breeding pairs. This dramatic decline has led conservation groups to petition for federal Endangered Species Act protection for the saltmarsh sparrow.
| Year | Estimated Breeding Pairs |
|---|---|
| 2002 | 30,000 |
| 2020 | 6,000-9,000 |
Some regional subspecies, like the Cape Sable seaside sparrow in Florida, have fared even worse, with a 90% population loss over the past several decades.
Conservation Status
Due to dramatic population declines, the saltmarsh sparrow is listed as a threatened or endangered species in the following states:
- Maine – Threatened
- New Hampshire – Endangered
- Massachusetts – Endangered
- New York – Endangered
- New Jersey – Endangered
- Delaware – Endangered
- Maryland – Endangered
- Virginia – Endangered
- North Carolina – Threatened
- South Carolina – Threatened
- Georgia – Threatened
- Florida – Threatened
It is currently not protected under the federal Endangered Species Act. However, several conservation groups have petitioned for it to be federally listed as threatened or endangered.
Conservation Efforts
A variety of conservation efforts are underway to try and protect remaining saltmarsh sparrows and stabilize the population.
Habitat Protection and Restoration
Protection of existing saltmarshes from development and draining is a key conservation priority. Habitat can also be restored and expanded by breaching dikes to restore tidal flow and planting native marsh vegetation.
Predator Control
In key nesting sites, predators like snakes, raccoons, and rats can be trapped and removed. Installation of predator exclosures around nests can also help increase nest success.
Public Education
Education efforts focused on private landowners, boaters, and coastal residents can help reduce disturbance of saltmarsh habitats and nesting birds.
Monitoring and Surveying
Continued monitoring and surveying of saltmarsh sparrow populations will be needed to track population trends and assess conservation efforts over time.
Captive Breeding
Some zoos and nature centers have started captive breeding programs to establish a captive “insurance” population of saltmarsh sparrows.
Nest Relocation
Experimental efforts to physically relocate nests to higher elevations have shown some success at reducing flooding impacts.
Reducing Mercury Pollution
Reducing emissions from coal power plants and incinerators can help decrease mercury contamination in coastal wetlands.
Conclusion
In summary, saltmarsh sparrows are highly threatened by habitat loss, nest flooding, predation, lack of genetic diversity, and mercury poisoning. Conservation efforts are underway, but without major intervention it is likely this unique tidal marsh bird will go extinct in the coming decades. Protecting and restoring saltmarsh habitats is essential to preserving saltmarsh sparrows, as well as the many other species that rely on these important coastal wetlands.
