Saltmarsh Sparrow Life History

Habitat

Saltmarsh Sparrows are restricted to tidal saltmarshes throughout the year. For nesting, they generally prefer higher-elevation, drier portions farthest removed from the reach of the tide (known as supratidal areas), though this varies locally. Saltmeadow cordgrass, saltgrass, and needlerushes are key parts of the breeding habitat, but some birds nest in the upper intertidal parts of the marsh, in smooth cordgrass. In winter they use very similar habitats, although their winter ecology in Florida and on the Gulf Coast has not yet been studied. Migrants use tidal marshes near the Atlantic coast. In May and October, grounded migrants often rest on the artificial islands of the Chesapeake Bay Bridge-Tunnel at the mouth of Chesapeake Bay. During strong nor’easters and snowstorms, Saltmarsh Sparrows take refuge in eastern redcedar trees bordering saltmarshes; these dense evergreen trees sometimes also provide overnight roost sites during clear weather in the nonbreeding season.

Food

Saltmarsh Sparrows eat mostly adult and larval insects, amphipods, and spiders, along with some seeds of marsh plants. During the breeding season, they eat almost exclusively animal matter, including tiny fish and mollusks on occasion. All of the insects known in the species’ diet —including flies, butterflies, moths, aphids, grasshoppers, leafhoppers, crickets, weevils, ladybugs, tiger and ground beetles, rove beetles, and click beetles—are closely associated with their saltmarsh habitat. After breeding, local Saltmarsh Sparrows strip seeds of smooth cordgrass from their seedheads. Although most foraging is done on or near the ground, Saltmarsh Sparrows are opportunistic, readily moving higher into marsh vegetation if insects and seeds are available there.

Nesting

Nest Placement

The female selects the nest site, usually in higher (or supratidal) parts of the marsh, above the mean high water zone. This part of the marsh is dominated by saltmeadow cordgrass, which forms a mat (often called “thatch”) on top of which nests are sometimes placed to avoid inundation during high tides. Nests are usually less than 3 feet off the ground. Occasionally they rest on the ground at the base of a clump of needlerush, marsh elder, or other shrub.

Nest Description

The female constructs the nest, which is a simple, bulky cup of marsh grasses and reeds, supported by stems of marsh plants at the sides and often by mats (thatch) of saltmeadow cordgrass below. Females sometimes build a partial dome over the top of the nest. Males don’t help raise young; females normally approach the nest from some distance on the ground, through tunnels beneath the thatch of cordgrass. Nests average 2.8 inches tall by 3.4 inches across, with the interior cup 2 inches across and 1.5 inches deep.

Nesting Facts

Behavior

Saltmarsh Sparrows spend much of their time foraging, especially during falling tide and low tide, when more parts of the marsh are exposed. Most observations indicate that they feed on the ground, where the bulk of the available food consists of insects and other arthropods. These sparrows may even forage at night under the moon. Saltmarsh Sparrows are well adapted to unpredictability in food supplies and put on fat quickly to survive storms with high tides and surges. In spring, when breeding, male Saltmarsh Sparrows move around large areas of marsh, seeking females, and apparently only deliver their quiet song when they find a female. Receptive females solicit copulation, but males often chase unreceptive females and copulate despite resistance on the part of the female.

Conservation

Saltmarsh Sparrow populations are declining rapidly. Rangewide surveys estimated a decline of about 9% per year between 1998 and 2012, indicating an overall loss of 75% of the global population in that time. Partners in Flight estimates the global breeding population is 60,000 and rates the species a 19 out of 20 on the Continental Concern Score. It is on the Red Watch List, Partners in Flight’s highest level of conservation concern. Factoring in the bird’s small population size and declining trend with the reality of rising sea levels, this species is in very real danger of extinction within the next few decades. Among the species’ problems, sea level rise is the most difficult to address: the birds nest in vegetation that stands only inches above the water (nests are often inundated for short periods by high tides), and coastal development will make it difficult for saltmarsh habitat to move inland as sea levels rise. The species is also threatened by further habitat loss due to development, habitat degradation from poor water quality and polluted runoff, and invasive plants such as Phragmites. Saltmarsh Sparrows tend to acquire higher levels of toxic mercury than Seaside and Nelsons’ Sparrows from the same areas, so they may be more susceptible to mercury pollution. Suggestions to help the Saltmarsh Sparrow survive sea level rise fall into short-term solutions, such as restricting tidal flows to reduce the effects of the highest tides; and long-term solutions, such as protecting adjacent uplands for marshes to move into, reducing marsh erosion, and encouraging sediment flow to allow marshes to enlarge.

Credits

Correll, M. D., W. A. Wiest, T. P. Hodgman, W. G. Shriver, C. S. Elphick, B. J. McGill, K. M. O'Brien, and B. J. Olsen (2017). Predictors of specialist avifaunal decline in coastal marshes. Conservation Biology 31(1):172–182.

Cristol, D. A., F. M. Smith, C. W. Varian-Ramos, and B. D. Watts. (2011). Mercury levels of Nelson's and Saltmarsh sparrows at wintering grounds in Virginia, USA. Ecotoxicology 20 (8):1773-1779. doi: 10.1007/s10646-011-0710-5.

Greenlaw, Jon S. and James D. Rising. (1994). Saltmarsh Sparrow (Ammodramus caudacutus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

North American Bird Conservation Initiative. (2014). The State of the Birds 2014 Report. US Department of Interior, Washington, DC, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

Smith, F. M. (2012). Photo Essay: Subspecies of Saltmarsh Sparrow and Nelson’s Sparrow. North American Birds 65:368–377.

Walsh, J., I. J. Lovette, V. Winder, C. S. Elphick, B. J. Olsen, G. Shriver, and A. I. Kovach. (2017). Subspecies delineation amid phenotypic, geographic and genetic discordance in a songbird. Molecular Ecology 26 (5):1242-1255. doi: 10.1111/mec.14010.

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