Demography and Populations

Measures Of Breeding Activity

Age At First Breeding

Both sexes begin breeding spring after hatching year.

Clutch

Two to 5 eggs. Modal clutch in northeastern salt marsh populations (A. m. maritimus) is 4. More southerly salt-marsh groups have modal clutch of 3. Mean clutch size: NY, 3.66 (SD 0.59, n = 272, range 2–5); South Atlantic group (N. Carolina to Florida), 3.06 (0.49, 100, 2–5; Charleston Museum ); n. Florida (A. m. peninsulae), 3.08 (0.31, 108, 2–4; Post et al. 1983). East-central Florida (A. m. nigrescens), 3.60 (0.53, 91, 2–4; Clemson Univ. Western Foundation Vertebrate Zoology); Florida Everglades (A. m. mirabilis), 3.53 (0.70, 19, 2–4; Stimson 1968, Werner 1975).

As with other saltmarsh sparrows, though clutch size varies with latitude, predation pressure may be a more important factor in explaining differences in clutch size among populations -- within Ammodramus, significant negative relationship between clutch size and predation rates. No relationship to loss due to flooding (Greenberg 2006).

Annual And Lifetime Reproductive Success

Mean annual reproductive success in northeastern populations about the same as that of other marsh-nesting passerines in Northeast (Post 1986). Although territory sizes, commuting distances, and feeding behavior differed greatly between ditched and natural salt marshes, reproductive success did not (Post 1974, Greenlaw 1992). Probability of nest survival during 12-d incubation period (Mayfield 1975): Oak Beach, NY, 1977 (n = 64 nests): 0.565; 1978 (82): 0.580; Gulf Hammock, FL, 1979 (34): 0.032; 1980 (43): 0.118. Everglades, FL 1995-1999 early nests (91; before 1 Jun): 0.66; late nests: 0.58 (Lockwood et al. 2001). Survival probability of nest during 9-d nestling period: NY 1977 (n = 64): 0.560; 1978 (n = 82): 0.659; Gulf Hammock, FL 1979 (n = 34): 0.194; 1980 (n = 43): 0.403.

Number of young fledged /female/yr: Massachusetts: 3.97 (2-yr mean; 3.46–4.47; Marshall and Reinert 1990); New York: 4.43 (4-yr mean; 3.38–5.77; Post and Greenlaw 1982); Florida: 0.58 (2-yr mean; 0.17–0.99; Post et al. 1983).

Estimated lifetime reproductive output of average female (productivity discounted by survival = estimated replacement rate): 2.72 in New York, 1.11 Gulf Hammock, FL (Post et al. 1983).

Life Span And Survivorship

Non-migratory populations: Minimum survival rates in S. Carolina (macgillivraii: lower 95% confidence limit, based on mark-recapture; WP):

Nestlings (n = 99; 1999-2003), survival to independence in hatch-year: 30%.

Juveniles (85 marked in 2000): hatch year–year 1: 10.4 %; year 1-2: 97.6%; year 2-3: 19.1%; year 3-4: 11.0%; year 5-6, 8.8%.

Adult males (154 marked in 2000). year 1-2: 72%; year 2-3: 58% year 3-4; 53% year 4-5: 32%.

Adult females (66 marked in 2000): Year 1-2: 52%; year 2-3: 18%; year 3-4: 38%; year 4-5: 14%

Minimum annual survival of adult males in n. Florida (A. m. peninsulae) 85.7% (Post et al. 1983). Estimated as 88% for mirabilis (Werner 1975); more recent survival estimates are: 63%; most optimistically, 69% (19 adults, 1997-1998; Morrison and Dean 1999) and 66% (265 adults, 1994-1998; Lockwood et al. 2001). Sexes of mirabilis have similar return rates: males: 26-52%; females, 25-45%. Return rate for juveniles 15-20%. No information on first year survival, as no banded nestlings recaptured in same year (Lockwood et al. 2001).

Migratory populations: Minimum annual survival of breeding adult maritimus (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 lower, or dispersal greater than in non-migratory groups. Survival from fledging to independence: NY, 36% (n=126) (Post and Greenlaw 1982). In Massachusetts, none of 35 nestlings banded in 1985 were seen the following year.

Potential life span of males and females of several populations reported as 8–9 yr (Sykes 1980, M. V. McDonald pers. comm., WP).

Disease And Body Parasites

Of 206 adults examined in New York, 60% had feather lice (Mallophaga; Philopterus subflavescens). Males infested more often than females (Post and Enders 1972). Soft ticks (Argasidae; Haemaphysalis chordeilis) found on 2 of 206 birds (WP; Peters 1936). Avian louse flies (Hippoboscidae) noted on 1 of about 500 birds examined in New York.

Seaside Sparrows in N. Carolina often infected with helminths: of 100 examined, only 2 were worm-free. 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 1 species, nematode Microtetrameres cruzi, produced visible pathogenic effects: proventricular walls of 3 hosts were damaged (Hunter and Quay 1953).

Fowl pox rarely seen; of about 500 adults examined at Oak Beach, NY (1976–1978), only 2 had obvious lesions.

Causes Of Mortality

Daily nest mortality rates in n. Florida were 19.4%, versus 3.3% in New York (Post et al. 1983). In NY and Massachusetts, main known mortality factor for nest contents in some years was storm-related flooding (New York: 24% of lost eggs, 38% of lost young, Post et al. 1983; Massachusetts: 89% of nests, Marshall and Reinert 1990). Main known cause of nest failure in n. Florida was assumed to be predation by rice rats (28% of losses) and Fish Crows (12%) (Post 1981a). Predation also a major source of nest mortality in NY (40.9% of total eggs lost, 63.1% of total young lost). In NY, 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 (Baiser et al. 2008); 41% of eggs laid March-early June produced fledglings (30% of mortality due to predation); value dropped to 13% for late-season nests, (67% of nests depredated) (Lockwood et al 2001).

Little direct 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 (Werner and Woolfenden 1983). During an Everglades fire, Werner (1975) saw sparrows fly to adjacent unburned areas, and circle in areas of smoke and flames. After a 1975 fire that burned 850 ha of A. m. nigrescens habitat on St. Johns River, FL, only 7 of 36 banded males could be found (Walters 1992)

Storms may have little direct effect on adult survival. Population at Cape Sable, FL (A. m. mirabilis) survived September 1935 hurricane, which had winds of 220 km/h (Semple 1936). Between 1871 and 1973, eight hurricanes passed over Cape Sable but apparently did not affect sparrows in that area (Werner 1975). The hurricane of August 1992, however, was estimated to have reduced the mirabilis population from 6,000 to 4,000 (Pimm et al 1994; but see Curnutt et al. 1998).

After severe storm over Grande Isle, Louisiana in April 1993, three 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 (Wiedenfeld and Wiedenfeld 1995), but this number is highly improbable, as it was based on the assumption that Seaside Sparrows are trans-Gulf migrants.

Range

Initial Dispersal From Natal Site

As in other saltmarsh sparrows (Greenberg et al. 2006), natal dispersal is limited. In S. Carolina (macgillivraii), no apparent difference between male and female post-fledging dispersal distances: males (n=8): 268 m, range 55-602 m; females (4): 156 m: 20-294 m. Dispersal rates also similar: males (8): 5.5 m/d, range 1.3 – 12.6 m/d; females (4): 6.8 m/d, range 1.1-18.4 m/d (WP). In Florida (mirabilis), natal as well as adult breeding dispersals occasionally > 1 km (Dean and Morrison 1999); 15 juveniles moved an average of 577 m, compared to adult dispersal of 212 m (Lockwood et al. 2001). After breeding season, juveniles in NY wandered up to 2.5 km from natal site, usually to feeding sites in tall S. alterniflora (WP). A nestling banded at East Quogue, NY, was caught 70 d later, 65 km west.

In S. Carolina, distance between fledging site and first year (breeding) site was limited, and the same for both sexes: males (34): 234.1 m ± 28.8 SE, range 4-552 m; females (26): 242.4 m ±12.7 SE, range 81-688 m. No indication of additional dispersal following first breeding season; distances, fledging to year two: males (13): 304.5 m ± 50.5 SD, range 38 – 596 m; females (10): 286 ± 21.8 m; 55-724 (WP, unpubl. data).

Fidelity To Breeding Site And Winter Home Range

In a migratory population ( NY), males reoccupied the same territories in succeeding years. When insufficient cover remained after a severe winter, they nested near previous territories. The mean distance between 1970 and 1971 nests of 9 males was 13.6 m (9.4 SD, range 1–28; Post 1974). After nest destruction, both sexes renested within same territory (24 cases in NY; Post 1974). During breeding season, male A. m. nigrescens on Merritt Island, FL, moved 1.6 km from original banding site, then returned, both movements apparently in response to variation in feeding conditions in marsh impoundments (Sykes 1980).

Nonmigratory (n. Florida) birds stayed in or near breeding territory all year (WP). In S. Carolina, the winter return rate of birds, assumed to be migrants, was about 30% (Austin 1966).

Over 5 yr (1994-1998), return rates of adult mirabilis to breeding areas varied from 29% to 45%; 2 years post-banding, it was 20-37%. Only 5% returned 4 yr after banding. Average between-year distance of territories: 212 m (n=30; Lockwood et al. 2001).

Dispersal From Breeding Site Or Colony

In S. Carolina, distance between fledging site and first year (breeding) site was limited, and the same for both sexes: males (34): 234.1 m + 28.8 SE, range 4-552 m; females (26): 242.4 m + 12.7 SE, range 81-688 m. No indication of additional dispersal following first breeding season; distances, fledging to year two: males (13): 304.5 m + 50.5 SD, range 38 – 596 m; females (10): 286 m + 21.8 SD; 55-724 m (WP, unpubl. data). Six of 13 nigrescens on Merritt I., FL, moved 1.2 km from 1 marsh impoundment to another. Two later returned to original capture point. Not known if such long-range movements were regular (Sykes 1980). Researchers have found no movement between 5 breeding populations of mirabilis in Everglades, FL (Curnutt et al 1998, Dean and Morrison 1998, Lockwood et al. 2001, Pimm et al. 2007).

Home Range

Activity space (home range) sizes vary among regions, habitats, and seasons; most differences appear to be attributable to variation in habitat quality (Greenlaw and Post 1985). Because adults often forage away from nest site, total activity space usually larger than territory (defended space). In an unaltered marsh (NY), mean foraging space was 1,039 m² (n = 21, range 170–5,135 m²). Area in which singing occurred was 47% size of foraging area; defended area was 38% of foraging area. In ditched marsh (NY), mean foraging space was 8,121 m² (range 11,520–17,510 m²). Singing area was 58%, and defended area was 40%, of foraging space (Post 1974).

Cape Sable Seaside Sparrow (mirabilis) relatively sedentary in non-breeding season; 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. (Dean and Morrison 1999).

Population Status

Density

Densities (males/ha): ditched marshes, 0.6–1.0 (Woolfenden 1956, Post et al. 1983, DeRagon 1988); unaltered marshes, 0.3–20.0 (Springer and Stewart 1948, Quay 1953, Norris 1968, Werner 1975, Post 1970, Post 1981b).

No firm estimates of winter population densities, although Beaton’s (2003) observation of 228 birds gathering on an 8 m² island suggests large number winter within a circumscribed area. See also data from Christmas Bird Counts: Figure 10.

Numbers

Highest breeding densities reported from Long I., NY (Oak Beach) Delmarva Peninsula (Little Creek, DE, Elliott’s Island, MD; Greenlaw 1992). Species extirpated from east coast of Florida south of Duval Co., and other than A. m. peninsulae/ juncicola, most Florida populations small and disjunct (Kale 1983). McDonald (1988) estimated the population of sparrows on NW Gulf of Mexico (peninsulae and juncicola) to contain 5,000-10,000 birds. The Atlantic coast group (maritimus/macgillivraii) has the most extensive range, from s. Georgia to Long Island; however, no estimate of overall population size has been made.

A. m. nigrescens had a very limited distribution in e. central Florida (Merritt I. and adjacent St. Johns River marshes). In 1968, about 900 males, and presumably equal number of females, remained (Sharp 1970). Population was extirpated by 1980 (Delany et al. 1981). Cause of decline on Merritt I. was impoundment of salt marshes and, probably, spraying of insecticides (Sykes 1980). On St. Johns River, drainage and resulting uncontrolled fires may have destroyed most of birds (Baker 1978).

A. m. mirabilis occupies much of its historical range. As of 1982 it was widely distributed over 27,800 ha of s. 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). 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, pers. comm.); in 2007 the population was estimated at 3,184 birds in 5 separate groups. The largest group, “population B,” had about 2,512 pairs (Pimm et al. 2007).

Trends

Last species-wide assessment of breeding distribution was Robbins 1983. Overall, species is secure, but sparsely distributed in some regions (Florida and New England; Greenlaw 1992). Pooled Breeding Bird Survey (BBS) data from Florida, Delaware, Maryland, and New Jersey suggest population increased by about 4% annually from 1966 to 1989. Across Northeast, BBS data indicate annual increase of 2.1% from 1966 to 1990, but data must be treated with caution as they are based on only 13 routes (Greenlaw 1992). Further details from BBS data, 1966-2007, can be found at: http://www.mbr-pwrc.usgs.gov/cgi-bin/atlasa99.pl?05500&1&07.

Population Regulation

Species occupies intermediate position along moisture gradients (Sharp 1970, Greenlaw 1983). Small changes in marsh relief may have large effects on vegetative structure and thus on sparrow abundance (Greenlaw 1992).

Natural successional changes that convert low (intertidal) into high (supra-tidal) marsh (Niering and Warren 1980) represent problem over period of several hundred years (Redfield 1972). High marshes provide marginal sparrow habitat (Reinert et al. 1981). 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 (Kale 1983).

In low-marsh habitats, at least, some populations able to grow or stabilize replacement rates in face of losses from flooding or predation (Post et al. 1983). Adults renest quickly after nest loss and recolonize other sites on marsh (Post 1974, Greenlaw 1983, Marshall and Reinert 1990). Although able to use some ditched marshes, species does so only at reduced densities.

Fluctuations in numbers reported from some areas. Between 1974 and 1975, male population at Taylor Slough, FL, increased 75% (Werner 1975). Most populations in unaltered salt marshes relatively stable; e.g., at Gulf Hammock, FL, over 6 yr, density varied between 1.6 and 2.6 males/ha (M. V. McDonald pers. comm., WP).

Because of narrow coastal range, 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 (Tomkins 1934). In northern part of range, sizes of overwintering populations determined by severity of weather (Bull 1974).

Disappearance of birds from local areas after large-scale catastrophes probably due to habitat alteration rather than direct mortality of adults (Pimm et al. 2007). Small-scale fires cause temporary displacement of residents, which quickly move back (Baker 1973); uncontrolled fires probably destroy even birds capable of flight (Baker 1973, Werner 1975, Sykes 1980).

In east Everglades FL, A. m. mirabilis severely threatened because of drainage, invasion of exotic trees, frequent human-caused fires, and agricultural and urban development (Kushlan and Bass 1983). Reduction of western Everglades population in Big Cypress, FL, attributed to water-level manipulations (Pimm et al 2007).

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