Seaside Sparrow Ammospiza maritima Scientific name definitions

Jon S. Greenlaw, W. Gregory Shriver, and William Post
Version: 2.0 — Published July 1, 2022

Demography and Populations


Demographic rates vary substantially across the range in relation to migratory status, habitat quality, and environmental factors like the timing of disturbance (e.g., fire, precipitation). Predation and flooding are major causes of nest failure throughout the range and the influence of these two factors varies locally by site and regionally by latitude. The global population based on the North American Breeding Bird Survey (BBS) was estimated to be 200,000 individuals (95% CI: 32,000, 520,000) from 2006–2015 (216); however, the population estimate for the northeastern United States (Virginia to Maine) was 234,000 (112,000, 356,000) from 2011–2012 (217), suggesting that the global estimate could be closer to 500,000.

Measures of Breeding Activity

Age at First Breeding

Both sexes begin breeding spring after hatching year.


Clutch size ranges from 2 to 5 eggs. Modal clutch in northeastern salt marsh populations (A. m. maritima) is 4 eggs. More southerly salt-marsh groups have modal clutch of 3 eggs. Mean clutch size: New York, 3.66 ± 0.59 SD (range 2–5, n = 272); South Atlantic group (North Carolina to Florida), 3.06 ± 0.49 SD (range 2–5, n = 100) (Charleston Museum); northern Florida (A. m. peninsulae), 3.08 ± 0.31 SD (range 2–4, n = 108) (3). East-central Florida (A. m. nigrescens), 3.60 ± 0.53 SD (range 2–4, n = 91) (Clemson University, Western Foundation Vertebrate Zoology); Florida Everglades (A. m. mirabilis) based on initial small sample size, 3.53 ± 0.70 SD (range 2–4, n = 19) (180, 161), but average clutch size based on subsequent large sample sizes (n = 160, 175) were 3.1 ± 0.80 SD and 3.4 ± 0.66 SD (9, 197).

As with other saltmarsh-breeding sparrows, though clutch size varies with latitude, predation pressure may be a more important factor in explaining differences in clutch size among populations—within the former Ammodramus, there is a significant negative relationship between clutch size and predation rates. No relationship to loss due to flooding (134).

Annual and Lifetime Reproductive Success

Period nest survival varies among sites, years, and in response to disturbance ranging from 0.013 to 0.530 (Table 3). Lowest period nest survival estimates were documented in Georgia (201) and Maryland (218). In Georgia, there seems to be a clear tradeoff between the competing risks of nest failure caused by flooding vs. predation and the strength of these risks varies annually (201). In Maryland, extremely high precipitation events occurring in May and June caused nearly catastrophic nest flooding leading to low estimates of nest survival (218). Substantial research has been conducted on the patterns in nest survival for Cape Sable Seaside sparrow indicating variation within the subpopulations as well as in response to fire (8, 135, 219, 198).

Mean number of young fledged per female each year: Massachusetts: 3.97 (range 3.46–4.47, n = 2 yr) (117); New York: 4.43 (range 3.38–5.77, n = 4 yr) (163); New Jersey from 2011–2015: 2.65 (95% CI:2.21–3.09; 220); South Carolina: 2.50; Georgia: 1.90; Florida: 2.47 (67) and 0.58 (range 0.17–0.99, n = 2 yr) (3).

Estimated lifetime reproductive output of average female (productivity discounted by survival = estimated replacement rate): 2.72 in New York, and 1.11 Gulf Hammock, Florida (3).

Life Span and Survivorship

Life Span

Potential life span of males and females of several populations was reported as 8–9 years (138; M. V. McDonald, personal communication; WP). The oldest known individual was a male banded as an adult in South Carolina in 2005 and recaptured there in 2014 at a minimum of 10 years of age (221).


Survival rates for migratory (maritima) and resident subspecies are provided below; information is limited regarding survival to first year of independence.

A. m. maritima. Minimum annual survival of breeding adults (based on cumulative return rates): 1967–1972 year classes, calculated through 1980: females 60.4% (n = 169); males: 57.0% (n = 214); 1976–1977 year classes, through 1980: females, 41.4% (n = 58); males, 52.8% (n = 269). Survival of juveniles was lower, or dispersal greater, than in nonmigratory groups. Survival from fledging to independence (from departing nest to no longer being brooded by adults): New York, 36% (n = 126) (163). In Massachusetts, none of 35 nestlings banded in 1985 were seen the following year. In Connecticut, apparent adult survival was 72.0–89.6% (110). In New Jersey, apparent adult survival was 61.6% (95% CI: 52.5, 70.0) (5). During five nonbreeding periods (2006–2010) in North Carolina, apparent adult survival was 48.3% (142).

A. m. macgillivraii. Minimum survival rates in South Carolina (lower 95% confidence limit, based on mark-recapture; WP, unpublished data). For nestlings (n = 99, marked 1999–2003): survival to independence, 30%. Juveniles (n = 85, marked in 2000): hatch year (from independence)–year 1, 10.4%; year 1–2, 97.6%; year 2–3, 19.1%; year 3–4, 11.0%; and year 5–6, 8.8%. Adult males (n = 154, marked in 2000): year 1–2, 72%; year 2–3, 58%, year 3–4, 53%; year 4–5, 32%. Adult females (n = 66, marked in 2000): year 1–2, 52%; year 2–3, 18%; year 3–4, 38%; year 4–5, 14%.

A. m. peninsulae. Minimum annual survival of adult males in northern Florida was 85.7% (3).

A. m. mirabilis. Annual adult survival for Cape Sable Seaside Sparrow was estimated as high as 88% in the 1970s (161), 63–69% (19 adults, 1997–1998; 131), 66% (265 adults, 1994–1998; 135) in the 1990’s, and more recently, 60% (93 adults from population E, 2002–2007 (222). Boulton et al. (222) captured 498 juveniles (96% captured as nestlings and 4% captured as fledglings) from 1998–2007 and estimates of juvenile survival rate ranged from 9% in 2000 to 47% in 2002. Sexes of mirabilis have similar return rates: males: 26–52%; females, 25–45%. Return rate for juveniles 13%. No information on first-year survival, as no banded nestlings were recaptured in same year (135).

Disease and Body Parasites

Body Parasites

Of 206 adults examined in New York, 60% had feather lice (Mallophaga; Philopterus subflavescens); males were infested more often than females (37). Soft ticks (Argasidae; Haemaphysalis chordeilis) were found on 2 of 206 birds (WP; 223). Avian louse flies (Hippoboscidae) were noted on 1 of about 500 birds examined in New York (WP).

Individuals in North Carolina were often infected with helminths; only 2 of 100 examined were worm-free (224). Infected birds had 9 species of trematodes (42% infection rate), 3 species of cestodes (51%), 2 species of Acanthocephala (83%), and 7 species of nematodes (59%). Only one species of nematode (Microtetrameres cruzi) produced visible pathogenic effects: proventricular walls of 3 hosts were damaged (224).

Fowl pox has rarely been reported; only 2 of about 500 adults examined at Oak Beach, New York (1976–1978) had obvious lesions (WP).

Causes of Mortality

Daily nest mortality rates in northern Florida were 19.4%, versus 3.3% in New York (3). In New York and Massachusetts, the primary known mortality factor for nest contents in some years was storm-related flooding (New York: 24% of lost eggs, 38% of lost young [3]; Massachusetts: 89% of nests [117]). The main known cause of nest failure in northern Florida was assumed to be predation by marsh rice rat (Oryzomys palustris) and Fish Crow (Corvus ossifragus) which accounted for 28% and 12% of losses, respectively (119). Predation was also a major source of nest mortality in New York (40.9% of total eggs lost, 63.1% of total young lost) and New Jersey (220, 5). In New York, hatching failure accounted for 11.3% of egg mortality. In Florida Everglades, early season nests were more successful than those initiated later. Seasonal effect due to changes in predator abundance, which was related to increased water levels at onset of wet season (198); 41% of eggs laid from March to early June produced fledglings (30% of mortality due to predation); value dropped to 13% for late-season nests, (67% of nests depredated) (135).

Little information on mortality factors of independent birds. Although nests always vulnerable, fires with multiple ignition points (usually human-caused) may also kill adults and fledglings (7). During an Everglades fire, Werner (161) saw sparrows fly to adjacent unburned areas, and circle in areas of smoke and flames. After a fire in 1975 that burned 850 hectares of A. m. nigrescens habitat on St. Johns River, Florida, only 7 of 36 banded males could be relocated (225)

Storms may have little direct effect on adult survival. Population at Cape Sable, Florida (A. m. mirabilis) survived September 1935 hurricane, which had winds of 220 km/h (226). Between 1871 and 1973, 8 hurricanes passed over Cape Sable, but apparently did not affect sparrows in that area (161). The hurricane of August 1992, however, was estimated by Pimm et al. (227) to have reduced the mirabilis population from 6,000 to 4,000 (but see Curnutt et al. [139]).

After severe storm in April 1993 over Grande Isle, Louisiana, 3 Seaside Sparrows were found washed up during search of 30 km of shoreline; it was estimated, by extrapolation, that a total of 111 Seaside Sparrows had been killed in the storm (228), but this number seems improbable, as it was based on the assumption that Seaside Sparrow is a trans-Gulf migrant.

Population Spatial Metrics

Individual Distance

In breeding period, physical contact occurs between fighting individuals. During mutual displays such as bobbing and wing-raising, neighboring males may approach within 20 cm of each other (169). At distances < 10 cm, fighting usually ensues. Nearest individual distances among captives 3–5 cm. No contact during roosting. In one instance, male attempted 6 times to preen another in head and shoulder region; each attempt was repulsed (WP). During February flood tides in Georgia, 228 Seaside Sparrows and 8 "sharp-tailed sparrows" [Ed: potentially both Saltmarsh Sparrow (Ammospiza caudacuta) and Nelson's Sparrow (Ammospiza nelsoni)] congregated on an 8 m2 grass island. Many birds were in contact, some “practically climbing on each others' shoulders in an attempt to find a perch (192).

Territory Size

Mean territory size: Buzzard's Bay, Massachusetts: 3,953 m2 (range 1,290–10,423, n = 17) (117); Narragansett Bay, Rhode Island: 4,545 m2 (range 944–8,837, n = 18) (176); Oak Beach, New York: 1,203 m2 (range 160–6,190, n = 25) (169); Tobay, New York: 8,781 m2 (range 810–17,640, n = 13) (116); Gulf Hammock, Florida: 1,600 m2 (range 200–3,200, n = 37) (3); Taylor Slough, Florida: 15,000 m2 (range 3,000–66,000, n = 43) (161); Ochopee, Florida: 36,000 m2 (range 7,000–8,000, n = 10) (7); St. Johns, Florida: 5,100 m2 (range 1,600–10,060, n = 14) (183).

Home Range Size

Activity space (home range) sizes vary among regions, habitats, and seasons; most differences appear to be attributable to variation in habitat quality (229). Because adults often forage away from nest site, total activity space usually larger than territory (defended space). In an unaltered marsh (New York), mean foraging space was 1,039 m2 (range 170–5,135, n = 21). Area in which singing occurred was 47% size of foraging area; defended area was 38% of foraging area. In ditched marsh (New York), mean foraging space was 8,121 m2 (range 11,520–17,510). Singing area was 58%, and defended area was 40%, of foraging space (116). In Delaware, territory density was over two times greater on marshes with limited Open Marsh Water Management (OMWM; 5.35 ± 0.60 territories/ha) than on marshes with extensive OMWM (2.39 ± 0.56 territories/ha; 4).

Cape Sable Seaside Sparrow (A. m. mirabilis) is relatively sedentary in nonbreeding period; winter home ranges, which often overlapped for adjacent males, averaged 12 ha. The movements of several radio-tagged birds were > 3 km; the longest was 7 km (131). Winter home ranges of mirabilis did not shift with changes in water depth; when water rose, sparrows occupied parts of home range that had fewer openings and higher vegetation such as sawgrass.

Population Status


Population Size

Using data from the North American Breeding Bird Survey (BBS), the global Seaside Sparrow population was estimated at 200,000 individuals (95% CI: 32,000, 520,000) from 2006–2015 (216).

Wiest et al. (217) estimated 234,000 individuals (range 112,000–356,000) for subspecies A. m. maritima from Virginia to the northern extent of the breeding range from 2011–2012. The population size of A. m. macgillivraii was estimated at 32,800 individuals occurring along 100 miles of coastline and divided into four breeding populations with three in South Carolina (North Inlet–Bulls Island, Headquarters Island, and ACE Basin) and one population in Georgia–Florida (67). Seaside Sparrow has been extirpated from the Atlantic coast of Florida south of Duval County (northeastern Florida), and other than A. m. peninsulae, most Florida populations are small and disjunct (49). In 1988, the population on northwestern Gulf of Mexico (peninsulae) was estimated to contain 5,000–10,000 birds (24).

A. m. mirabilis occupies much of its historical range. As of 1982, it was widely distributed over 27,800 ha of southern Florida west and east of Shark River Slough, but became rare or absent from Cape Sable and Ochopee areas as the habitat was altered (shrub invasion, hurricane effects). The main population is in or near Taylor Slough, and in 1992 included at least 6,640 birds. Only about 3,700 birds present in 1993 after Hurricane Andrew (J. Curnutt, personal communication); in 2007 the population was estimated at 3,184 birds in 5 separate groups. The largest group, “population B,” had about 2,512 pairs (140).

Historically, A. m. nigrescens had a very limited distribution in east-central Florida (Merritt Island and adjacent St. Johns River marshes). In 1968, an estimated 900 males, and presumably equal number of females, remained (230).


Highest breeding densities reported from Long Island, New York (Oak Beach) and Delmarva Peninsula (Little Creek, Delaware and Elliott's Island, Maryland) (113). Singing male densities in ditched marshes, 0.6–1.0 males/ha (2, 3, 176); densities in unaltered marshes, 0.3–20.0 males/ha (231, 232, 174, 161, 118, 130).

No estimates of winter population densities, although Beaton's (192) observation of 228 birds gathering on an 8 m2 island suggests a large number winter within a circumscribed area.


Survey-wide results from the BBS indicated a mean increase of 1.0% (95% CI: –1.1, 3.7; n = 28 survey routes) per year from 1966 to 2019 (233). Regional BBS trends during the same time period indicated potential declines; e.g., the New England/Mid-Atlantic Coast Bird Conservation Region (BCR 30) had a mean decrease of 0.9% (95% CI: –2.4, 0.4; n = 13 routes) per year (233). However, both survey-wide and regional results must be treated with caution given the limited sample size for BBS routes and the species' generally low abundance on surveys. Using a large point-count data set collected from Maine to Virginia, Correll et al. (234) reported no population trend for Seaside Sparrow between 1994 and 2012.

A. m. macgillivraii populations were recently reported to be declining in the southeastern United States (67).

A. m. mirabilis populations declined 58% between 1992 and 1995 (139). Historical site occupancy trends (surrogate of abundance) showed that this subspecies has experienced two episodes of decline, but recently while two subpopulations continue to decline in occupancy, one exhibits consistent increases (235).

A. m. nigrescens was estimated at 900 males in 1968, with presumably equal number of females (230), though the subspecies was extirpated by 1980 (236).

Population Regulation

The Seaside Sparrow occupies an intermediate position along moisture gradients (230, 115) and are therefore sensitive to hydrologic changes and the associated vegetation responses. Small changes in marsh relief may have large effects on vegetative structure and thus on sparrow abundance (113). Changes to vegetation structure driven by increased sea levels and the associated altered hydrology are predicted to have substantial impacts on populations (237, 218). Reducing marsh loss and limiting conversion of vegetation dominated marsh to mud flat or open water would have a positive impact on population persistence (218). In Georgia, the species currently use higher elevation areas within the marshes where they occur, a habitat that is predicted to decline by > 80% by the year 2100 (238).

Natural successional changes that convert low (intertidal) into high (supra-tidal) marsh (239) represent potential problems over period of several hundred years (240). Long-term changes in sparrow productivity resulting from succession can be expected even in protected tidal wetlands; e.g., climate change may favor invasion of salt marshes by mangroves (49) in the long term but shorter term time scales.

In low-marsh habitats, areas dominated by Spartina alterniflora and other plant species adapted to daily tidal inundations, some sparrow populations are able to grow or stabilize replacement rates in face of losses from flooding or predation (3). Adults renest quickly after nest loss and recolonize other sites on the same marsh (116, 115, 117). Historic structural alterations to salt marshes like mosquito control ditches dug in the 1920’s and 1930s are extensive throughout marshes along the Atlantic coast (241). The immediate effects of these alterations on sparrow population dynamics are not well documented, but there are clear shifts in vegetation community structure and composition with an increase in shrub cover and a reduction in open water (241). Invertebrate diversity and abundance did not differ between marshes ditched for mosquito control in the 1930s or unditched marsh (242) therefore one could surmise there would be no effect on sparrow food availability. There is a growing body of evidence indicating that historical ditching, installed nearly 100 years ago, does not negatively impact sparrow breeding success (116, 117, 4, 5). Fluctuations in numbers reported from some areas. Between 1974 and 1975, male population at Taylor Slough, Florida, increased 75% (161). Most populations in unaltered salt marshes relatively stable; e.g., at Gulf Hammock, Florida, over 6 years, density varied between 1.6 and 2.6 males/ha (WP; M. V. McDonald, personal communication). Coastal New Jersey populations were stable to 2050 based on a population viability model simulating the effects of sea-level rise on population persistence (6).

Because of the species' narrow coastal distribution, populations in any given area may be displaced by storms, fires, oil spills. Current gaps in distribution may be explained in part by history of such disasters (243). In northern part of range, sizes of overwintering populations determined by severity of weather (244).

Disappearance of birds from local areas after large-scale catastrophes probably due to habitat alteration rather than direct mortality of adults (140). Small-scale fires cause temporary displacement of residents, which quickly move back (183); uncontrolled fires probably destroy even birds capable of flight (183, 161, 138).

In the eastern Florida Everglades, A. m. mirabilis is severely threatened because of drainage, invasion of exotic trees, frequent human-caused fires, and agricultural and urban development (126). Reduction of western Everglades population in Big Cypress, Florida, attributed to water-level manipulations (140).

Recommended Citation

Greenlaw, J. S., W. G. Shriver, and W. Post (2022). Seaside Sparrow (Ammospiza maritima), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.seaspa.02