Seaside Sparrow Ammospiza maritima Scientific name definitions

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



Pair Formation

Figure 1. In a migratory population (New York), adult males (≥ 2 years of age) arrived on breeding marshes about 1 week before females beginning in late April (WP). Likewise in Connecticut, males began arriving a few days before females, but afterwards through May arrivals broadly overlapped (35). In contrast, at Gulf Hammock, Florida, males and females associated all year in or near breeding territory (WP). Males at latter site had cloacal protuberance (CP) as early as 9 March; earliest female brood patch was recorded on 22 March. In New York, CP of earliest arriving males beginning in late April developed rapidly from little or no development to apparent full development in most males by 15–20 May, when early eggs begin appearing in nests. Mean CP size from 15 May to mid-July was 9.0 mm (± 0.88 SD) wide and 5.7 mm (± 0.1.2 SD) high (n = 55); CP height varied most among individuals (coefficient of variation ~22%) compared to basal width (CV ~10%) (JSG, unpublished data). In New York, pairs seem to form soon after females arrive on male territories, but little information on process of pairing apart from sexual chases and male following (JSG).

First Brood

Date of first egg relatively constant among years. At Buzzard's Bay, Massachusetts, first egg dates 25 May (1985) and 26 May (1986) (117); at Narragansett Bay, Rhode Island, about 23 May (176). At Oak Beach, New York, mean date of first egg 19 May, and 20 July for last clutches (3). At Gulf Hammock, Florida, first eggs found on 24 March (1979) and 23 March (1980) (WP). At Taylor Slough, Everglades, Florida, clutches usually started in early March but as early as late February (7, 9), and fledglings were found as early as 30 March (203). In the southern Florida population, first eggs of the earliest clutches are laid on average 2.7 d ± 1.6 SD after nest completion (9).

Second/Later Broods

Repeatedly renests after nest failures. At Buzzard's Bay, Massachusetts, 64% of pairs nested twice, 36% nested 3 times (n = 39 pairs) (117). At Oak Beach, New York, 54% of pairs nested twice, 21% nested 3 times, and 4% nested 4 times (n = 17 pairs) (116). Two broods were raised successfully by some pairs in New York (JSG), but apparently only one brood fledged in Massachusetts (117). Two and three broods are now known in Cape Sable Seaside Sparrow (A. m. mirabilis) in Everglades National Park in southern Florida, and three successful broods were documented in at least one case (9). In the latter case, interbrood intervals (fledging from previous nest to first egg-laying in subsequent nest assuming modal clutch size of 3 eggs) was 32 days between first and second broods and 18 days between second and third broods.

Because of similar lengths of breeding cycle and lunar period, success is higher when birds renest immediately after spring tide floods (176). In Massachusetts, rapid renesting after large-scale flooding led to local synchrony; first eggs of replacement nests were an average of 6.3 d from date of destruction. Nests whose cycle extended as little as 1 day longer were flooded (117).

In Connecticut, by contrast, Gjerdrum et al. (204) found that although flooding was a major source of mortality, timing of nesting did not significantly affect reproductive success. Nesting success was improved by nesting in taller than average vegetation. At Oak Beach, New York, timing of first nests was not synchronized with normal tidal cycle; in one case, renesting immediately followed storm flooding. In New York, mean interval between nest failure and renesting was 5.5 d. Interval between fledging and start of second clutch was 17.5 d (WP, JSG). At Gulf Hammock, Florida, clutch completion dates occurred in two peaks, one in late March–early April and the other in early May. Second peak was composed of females whose first attempt failed; interval between failure and renesting was 7.8 d (3).

Brood overlap was noted in Massachusetts: a female completed new 3-egg clutch on same day that single young from earlier nest fledged (117). At Taylor Slough, Florida, female A. m. mirabilis may initiate new nests before earlier broods have fledged (7).

Length of Breeding Period

New York: 76.8 d (range 67–88, n = 4 yr); egg dates extend from early May to late July (JSG, unpublished data). fledglings appeared as early as late May, and nests contained young as late as 14 August (113). Breeding season lasts 96 d at Gulf Hammock, Florida, with last clutch completed in third or fourth week of June (3). In each year, 90% of clutches completed by last week of May. Range of egg dates in Rhode Island: 27 May–31 August (176); Massachusetts: 25 May–30 July (117); Merritt Island, Florida (Dusky Seaside Sparrow, A. m. nigrescens): 17 April–11 August ([WFVZ), later than for salt-marsh population at same latitude (Gulf Hammock). The typical range of egg dates for Everglades birds is 27 March–7 July (180, 161), but a very early nest with young initiated in late February is in the literature (161). Reports of an early seasonal range of egg dates varying from March through late July to early August indicate that these sparrows can nest for a period of 122–142 days (9). One successful three-brood sequence began with clutch completed for first brood on 31 March and ended with a third nest fledging two young on 24 July for a season length of 115 days, or about 38 days per clutch (9). The earliest A. m. mirabilis nest was found on 20 March 1997 (135) and the latest fledglings from a third brood occurred in early August (9); rarely a nest with eggs or with chicks is reported as late as early September (137, 9). Nesting regularly extends into August when rains are light and prairie not deeply flooded, (131). Average interbrood interval in a sample of nests was 31 days (from fledging to first egg laid in next nest) between the first and second attempts and 17 days between the second and third attempts (9). Nest starts decline as water depth approaches 25–30 cm (161, 205). Evidence suggests that the energetic demands of molt initiation is the important factor that brings the breeding season to a close in A. m. mirabilis, although overlap cases of late breeding and earliest body molt are known in late August and early September (137, 9).

In southern Florida, Boulton et al. (197) showed that time of laying of initial egg of first broods, within the envelope of photoperiodic regulation of gonadal maturation, is influenced by rainfall preceding timing of laying. Females initiated nesting up to 1 month earlier in years of greater rainfall compared to drier early seasons. Although territories are re-established as early as late February (128), earliest first eggs tend to occur as noted above in late March and can extend well into April (197).

Nest Site

Selection Process

Female selects nest site within male's territory. In Georgia, where predation exceeds flooding as a cause of nest loss, female appears to express adaptive plasticity in nest-site selection that may mitigate a trade-off between these two risks by building nests lower in vegetation on average in years of high predation risk; see Annual and Lifetime Reproductive Success (201).


In coastal marshes, spring tides determine lower point of nest placement. Upper point determined by availability of stable vegetation for nest support and by amount of cover above nest. In some years, appropriate substrates limited in spring because of destruction of grass by winter storms (116). Nest sites in New York, where nests were built exclusively in Spartina alterniflora, in the unditched marsh at Oak Beach, but could not be differentiated from randomly chosen sites, whereas those at Gulf Hammock, Florida, could be. While most nests in New York were placed in the upper intertidal zone in the unaltered marsh in New York, a number of nests in this marsh also occurred in ecotonal margins bordering the supratidal saltmeadow zone (high marsh, S. patens dominant), but these nests still were placed in tussocks of S. alterniflora (JSG). In the altered (ditched) marsh in New York, nests were placed outside the intertidal along elevated ditch banks and Spartina edges of spoil islands where shrubby vegetation (Iva) dominated; sparrows there commuted to foraging areas outside the supratidal where they nested (Post 1970, 1974). Main differences between Florida nest sites and random sites were lower height and lower density of vegetation around nests (3). Taller and denser cover such as black needlerush (Juncus roemerianus) in northwestern Florida may be little used because of rodent predation (119). In southern Florida, populations settle in areas of marl prairie with short hydroperiods where the dominant ground cover is Muhlenbergia filipes (9). In southern Mississippi (Jackson County), 47.3% of nests (n = 140) were built in Juncus roemerianus, 34.4% in Spartina patens (largely avoided in northern states except in a ditched marsh in New York, WP) (n = 102 nests), 12.2% in Distichlis spicata (n = 36), and only 4.4% in S. alterniflora (n = 13) (11). The variety of graminoid vegetation types selected as nest sites on the northern Gulf coast is notably greater than in other populations along the Atlantic coast. In extreme southern Texas (Cameron County), where Spartina marshes are scarce, female A. m. sennetti nests in stands of Batis maritima and Borrichea frutescens (77).

Site Characteristics

At Oak Beach, New York, mean height of nest (eggs) above ground was 14.2 cm ± 5.8 SD; mean height of vegetation above nest rim was 54.4 cm ± 12.6 SD (n = 94) (WP, JSG). In South Carolina, nest heights highly correlated with mean vegetation height at each plot at Tom Yaukey Wildlife Center, Georgetown County. Mean nest height across plots was 31.3 ± 1.4 cm (SD), range 17.5 to 42 cm (68). At Gulf Hammock, Florida, height of nest was 27.7 cm ± 8.2 SD and height of vegetation was 71.9 cm ± 14.4 SD (n = 47) (WP). At Taylor Slough, Florida, mean nest height was 18 cm (range 6–37, n = 16) (7). In southern Mississippi, mean nest height was 37 cm ± 16.8 SD (range 11–104), reflecting the frequent use of black needlerush as a tall-graminoid nest site there (11). On Mustang Island, Texas, mean height of vegetation in which nests (n = 9) were placed was 100.5 cm ± 36.5 SD and mean nest height (ground to bottom of cup) was 45.6 cm ± 15.1 SD (206). Within species range, nest height ranges from ground level to 4.3 m (WP).

Throughout range, most often nests in graminoid vegetation (Spartina, Distichlis, Sporobolus, Paspalum, Muhlenbergia, Juncus, Cladium, Typha, Phragmites) (Figure 12). Also uses wide variety of other substrates, ranging from woody vegetation (A. m. macgillivraii, 1.5 m high in the shrub Baccharis halimifolia under clumps of foliage; 53), black mangrove (Avicennia germinans), and marsh elder (Iva frutescens) to forbs (glasswort, sea-purslane, sea oxeye). In New York, nest sites in an unaltered marsh (Oak Beach) were dominated by an intermediate height-form of S. alterniflora in the upper intertidal. In contrast, individuals nesting in an altered marsh in New York used the drier parts of the marsh to nest and often placed nests in tussocks of S. patens at the bases of the shrub, Iva frutescens on ditch banks of spoil from the adjoining ditch (Post 1970). Specifically, In South Carolina, nest sites of macgillivraii average 15.8 % more saltgrass (Distichlis) and 24% less black needlerush cover than random vegetation plots (WP). No nests were placed where black needlerush thatch was present, perhaps because rice rats there are able to climb more easily to reach higher nests. All nests were built attached to 3 graminoid species: 22 in >50% smooth cordgrass, 4 in 50% black needlerush, 3 in >50% saltgrass, and 6 in graminoid ecotones (68). Also nests under tidal debris. Use of woody vegetation for nest placement is rare in most of the breeding range, but 8 of 9 nests found on Mustang Island, Texas, were placed in young (< 1 m) black mangrove invading a Distichlis spicata marsh (206).

At Merritt Island, Florida, A. m. nigrescens nested mainly in Sand Cordgrass (50% of 36 nests), black needlerush (22%), saltgrass (14%), and saltwort (11%) (Western Foundation Vertebrate Zoology [WFVZ]). At Gulf Hammock, Florida, A. m. peninsulae nested in saltgrass 48% of time (n = 114 nests), although saltgrass was only 24% of the cover. Glasswort was also used out of proportion to its coverage (25% use vs. 7% coverage). In contrast, black needlerush and S. alterniflora accounted for a majority of the vegetative cover, but were infrequently used for nesting in most areas (black needlerush: 15% use versus 37% coverage; S. alterniflora: 9% vs. 26%). Seaside Sparrow seldom nested in S. alterniflora because it grew at a lower elevation on marshes where there was increased probability of flooding; at higher elevations nest site selection may be affected by predators (119).

In Everglades, A. m. mirabilis nests mostly confined to marl prairie habitat dominated by Muhlenbergia filipes (muhly grass). Territories of A. m. mirabilis tend to be in areas with high muhly grass coverage, whereas sawgrass varied from 1.25 to about 5 times less prevalent on average (9). The percent cover of Muhlenbergia filipes and grasses in two other genera (Rhynchospora, Schizachyrium) were significantly higher than at random sites in the area. Pimm et al. (9) reported that characteristic vegetative features around A. m. mirabilis nests were effective cover twice as high and perches 3 to 4 cm higher than elsewhere on a territory. These authors suggested that presence of Muhlenbergia filipes, Rhynchospora spp., and Schizachyrium rhizomatum may be cues for nest placement.

In Jackson County, Mississippi, female sparrows chose nest sites that had more ground cover and taller vegetation than random sites, evidently in response to depredation risk. Successful nests were surrounded by a denser stand of plant stems than failed nests, which enhanced concealment. Successful nests also tended to be located in sites on marshes where other female sparrows had successful nests and where concurrent sparrow nest density tended to be greater, suggesting an absence of density-dependent predation on nests there. Possibly, settled sparrow density may be an indicator of high quality habitat in this population (11).


Construction Process

Female builds nest alone; though, captive males have been observed placing nest material in vegetation (162). Nests are woven of dead stems and blades of herbaceous plants in Florida Everglades (9), New York (JSG), and likely across range. Once nest is started, female continues building even when male is removed. One nest of A. m. mirabilis found in standing grass on 4 April was in the earliest stage of construction and had a loosely woven grass circle with no discernable sides or bottom; the nest held 3 eggs when it was revisited on 18 April (9). In some populations, early nests are built in clumped, partially erect dead grass and in tall, green stems later in season, which often have a loosely interlaced canopy over the nest (northeastern United States [WP, JSG]) that is not attached directly to it. The canopy, sometimes inappropriately described in the Seaside Sparrow as a nest "dome" (generally applied in ornithological literature to a completely enclosed nest with opening on lower side), may reduce risk of tidal floods washing chicks out of nests of Saltmarsh Sparrow (Ammospiza caudacuta) (207), which like Seaside Sparrow often also builds a nest canopy under similar circumstances (JSG, personal observation). In Tom Yaukey Wildlife Center, South Carolina, 81% of nests had a partial or complete canopy upon discovery (68). Of 16 nests found in three seasons at Taylor Slough, Everglades, 44% were canopied and 56% were cups without a canopy. On Mustang Island, Texas, 2 of 9 nests were reported as "canopied," but at least one of the these was placed in a black mangrove (Avicennia germinans) seedling where only low-growing saltgrass (Distichlis spicata) provided ground cover (206). Unlike the loosely interlaced canopy described above, Ubias et al. (206) described nest "canopies" in Texas as woven in a fashion similar to the more fibrous primary nest structure, suggesting that these were partially domed (i.e., one wall of nest extended partially over top of nest). Nicholson (179), writing about Seaside Sparrow nests in Florida, referred to "arched" nests, which also may be construed as partially domed nests in which the "dome" is an extended portion of the nest on one side and over-topping the cup.

Structure and Composition

Nest is typically a cup of grass stems and blades, lined with finer grass blades. However, nests near Corpus Christi, Texas, had a hardened, densely matted base of packed material unlike any other nests described for the species (206). In the northeastern United States, the nest is usually covered to some degree by overhead herbage and later in the season by a canopy that the female constructs by interlacing grass stems above the nest. Some nests are built under wrack or matted live vegetation. Mean percent cover above nest was 80.0% (range 15–100, n = 100) at Oak Beach, New York (JSG) and 76.9% (range 10–100, n = 46) at Gulf Hammock, Florida (WP). In New York, most nest entrances oriented between south and east (54% of 65 openings; JSG). In Everglades, Florida, 45% of 16 nests were sometimes built with canopy of dead grass above the nest; opening into nest usually facing east (7). Orientation was related to vegetative support rather than to temperature regulation (161).


At Taylor Slough, Florida, dimensions of nest cups (n = 15): outside diameter, 10 cm (range 8–13); inside diameter, 6 cm (range 4–7); inside depth, 5 cm (range 2–7); outside depth without canopy, 7 cm (range 4–11); outside depth including canopy (n = 6), 13 cm (range 7–19) (161, 7). On Mustang Island, Texas (n = 9), outside diameter, 10.9 cm ± 1.2 SD; inside diameter, 7.4 cm ± 1.3 SD; inside depth 6.0 cm ± 1.6 SD; outside depth, 7.9 CM ± 1.5 SD (206).

At Taylor Slough, Florida, dry mass of nests (n = 15) was 16.2 g (range 8.2–24.3) (161, 7).


The only information on nest temperatures is on A. m. macgillivraii from plots in Tom Yaukey Wildlife Center north of Charleston, South Carolina, where 9 successful nests and 7 unsuccessful nests were monitored with temperature dataloggers (68). Ambient air temperatures averaged about 26°C in mornings and 28°C in evenings. Mean morning and evening nest temperatures were 35°C and 35.4°C, respectively. During morning hours, successful nests averaged 1.0°C ± 0.3 SE warmer than unsuccessful nets (P = 0.05, df = 13); during evening hours, nest temperatures of successful and unsuccessful nests did not differ (P = 0.183, df = 14). At night, nest temperatures varied from 33° to 38°C and were most stable when the female incubated or brooded young. Daytime nest temperatures fluctuated with the female's activity (on or off nest). As daytime temperatures heated and cooled, and the female took off-bouts to forage, ambient temperature approached parity with nest temperatures by mid-day or were a few degrees above prevailing nest temperatures. In one nest, a striking drop in nest temperature occurred during a rain event and persisted for several hours suggesting that the nest may have been flooded. Of several structural, vegetative, and nest temperature variables measured, nest survival was best explained by mean duration of off-bouts, mean nest temperature, and nest height.

Maintenance or Reuse of Nests

Not reported. In a sample of 329 nests followed in A. m. mirabilis, none were observed being reused (9).

Nonbreeding Nests

Not reported.



Short ovate to ovate; elongation (length/diameter) is 1.31.


Mean diameter and length: Oak Beach, New York (A. m. maritima), 15.51 mm ± 0.79 SD (range 14.48–17.78, n = 63) × 20.28 mm ± 0.64 SD (range 19.02–22.56, n = 63) (JSG); Taylor Slough, Florida (A. m. mirabilis), 14.7 mm ± 0.27 SD (range 14.1–15.2) × 19.3 mm ± 0.27 SD (range 17.6–20.6) (7); Merritt Island, Florida (A. m. nigrescens), 15.11 mm ± 0.72 SD (range 14.50–16.25) × 19.84 mm ± 0.72 SD (range 19.02–20.92) (WFVZ). Runt eggs have not been reported.


Mean wet mass of fresh eggs, Oak Beach, New York, 2.6 g ± 0.21 SD (range 2.3–3.2, n = 58) (JSG); Taylor Slough, Florida, 2.3 g (n = 14) (161); Gulf Hammock, Florida, 2.63 g ± 0.15 SD (n = 24) (208). Mean dry mass of contents and eggshell, Gulf Hammock, Florida, 0.38 g ± 0.03 SD (n = 22). Lipid content 37% of dry mass, about same as in other altricial species (208). Mean dry mass of shell, A. m. maritima, 0.149 g (range 0.126–0.169, n = 82) (WFVZ); A. m. nigrescens, 0.128 g ± 0.69 (range 0.116–0.142) (WFVZ); A. m. peninsulae, 0.163 g ± 0.014 (n = 23) (208).

Eggshell Thickness

No information.

Color and Surface Texture

Ground color bluish white to grayish white, speckled and blotched with shades of brown, often more heavily on larger end. Surface texture smooth, but not glossy.

Clutch Size

In Everglades (A. m. mirabilis) population, females on average initiate egg laying 2.7 days after nest completed (SD 1.6, n = 14) (9). 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); peninsular Gulf coast 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), 3.1 ± 0.80 SD eggs (n = 160) (9) and 3.4 ± 0.66 SD (range 2–5, n = 175) (197). Mean clutch size across the breeding season in New York was initially fairly even with a decline at the end of the season (JSG, unpublished data); for mirabilis in southern Florida, mean clutch size of the first breeding attempt was significantly lower than the second and third attempts while the second attempt in mid-season averaged higher than the last attempt as ground water became high at the end of the season (197). These two seasonal patterns fall outside the pattern exhibited by single-brooded species, whereas the A. m. mirabilis pattern is typical of the pattern of variation exhibited by long-season, multiple-brooded species or populations within species generally (209, 210). Although wetter earlier conditions in the breeding season favored larger clutch sizes in early broods compared to late broods, average nest survival was negatively related to high average rainfall late in the season (range 12–36% deficit). Boulton et al. (197) argued that food-related processes affected early clutch sizes and broods the most while predation-related factors predominantly influenced late broods.

Egg Laying

One egg laid daily; rarely, one day elapses with no egg laid (JSG, WP).


Only female incubates. Female has single brood patch on lower abdomen. In New York, brood patch first evident 2–10 days before first egg. Incubation begins with laying of penultimate or last egg; in New York, 20% of nests exhibited asynchronous hatching (n = 100; JSG, unpublished data). Incubation period for A. m. maritima 12.2–12.4 d (211, 117, 113); for A. m. mirabilis 12 d (8) and 12.1 d ± 0.5 SD (n = 6) (9).


Parents remove eggshells, but leave unhatched eggs in nest. Hatching rates are high: at Oak Beach, New York, only 8% of eggs (9 of 115) failed to hatch in 1979 (JSG).

Young Birds

Growth and Development

Mass increases logistically (Figure 8). Growth rate constant (K) = 0.546. Time taken to grow from 10% to 90% of asymptotic weight = 8.04 d; ratio of nestling asymptotic weight to adult weight = 0.76 (163).

Day 0. Series of white neossoptiles present on posterior part of ventral tract and on back near uropygium. White egg-tooth present. Young give a 1-note peep call on hatching day, also gape (2).

Day 1. Feather papillae visible on capital, humeral, and alar tracts and on cervical and dorsal regions of spinal tract. Occasionally, papillae visible on crural tract and cervical region of ventral tract. Thick ridge of tissue forms over eyeball, where eyelids delaminate. Young can maintain upright position when begging, by resting on tarsi (7). Can move short distances by using feet and wings (2). May give double peep call.

Day 2. Eyelids open slightly on some birds. Papillae visible on all regions of capital and spinal tracts. On some birds, papillae begin to appear on femoral tract.

Days 3–4. Papillae present on caudal tract and all regions of ventral tract. Papillae prominent on all pterylae. Eyelids partly open on most birds.

Day 5. Most individuals have eyes fully open. Egg-tooth gone. Incoming feathers all remain sheathed. Buff color appears on spinal, femoral, crural, alar, and ventral tracts. Yellow tinge appears near alula on some birds. Reedy vocalization (“cedar call,” 7) given during begging. Peep call no longer given. Young still beg when nest disturbed.

Day 6. Juvenile remiges still sheathed, but tips of body feathers unsheathed on all but capital tract. Cowering begins. Young begin to utter distress vocalizations when handled. Eyes fully open for all individuals. Some may utter scree call.

Day 7. Sheaths of remiges change from blue to gray and begin to slough off. Breast streaking begins to appear. When handled, young attempt to escape. Young first give tuck call (7).

Day 8. Birds well feathered except for coronal region of capital tract. Breast streaks distinct. Scapulars have light edges. When disturbed, young are first capable of leaving nest. May fledge prematurely if nest disturbed.

Day 9. Young normally leave nest (2, JSG).

Sex Ratios and Sex Allocation

No information.

Parental Care


Only females observed to brood young (JSG, WP).


Both parents feed young. Female feeds more often on hatching day; thereafter, delivery rates of sexes are similar. Delivery rates (feedings/young/h) at Oak Beach, New York: female 2.00, male 2.08; delivery rates at Gulf Hammock, Florida: female 1.69, male 1.32 (3). In Florida Everglades, 52% of food deliveries were by males (8). In New York, sexes flew similar average distance from the nest to a foraging site during food provisioning for nestlings (female 31 m ± 1.7 SD, n = 200); male 35 m ± 3.1 SD, n = 110) (163). Multiple items are brought to nests in a single delivery, with prey items often macerated and in a mucous-bound bolus. Mean volume of food delivered was 0.037–0.253 ml/h/nest (150). Frequency of large-sized items and total volume of food delivered to nest increased with nestling age (150). Females were able to adjust feeding rates to compensate for disappearance of males, and growth rates of male-orphaned young were the same as that of non-orphaned young (182). In the Everglades, radio-collared fledglings remained largely flightless and near the nests up to 8 days, but they remained dependent on parental care for a longer period (9). Indeed, very little is known about variation in the role of sexes in caring for young from fledging to independence. Limited evidence for Seaside Sparrow suggests that 8 to 9 days represents potential interbrood intervals between fledging of at least one young from a first nest to start of egg-laying in a second nest (117). This scenario likely assumes either that the male takes over full care of fledged young prior to independence and continues feeding them to independence, thus allowing its mate to start another brood early, or the young from the first nest succumb to depredation early. Marshall and Reinert (117) provided an example of unusual case of likely male care of fledged young in which a female was known to lay a third egg of a new clutch on the same day the single young from the previous nest fledged.

In unaltered marsh at Oak Beach, New York, relatively few arthropod groups were fed to nestlings, the 10 most important taxa comprised 94% of total volume delivered. Of 1,203 nestling food items, 14% could be classified as strictly mud-inhabiting organisms (e.g., immature flies). Food volume brought to nests was 28% immature (papal and larval) flies (21% Tabanidae; 7% Stratiomyidae) and 21% immature moths (Noctuidae); nestlings were fed large numbers of plant bugs (Trigonotylus tarsalis), although these comprised relatively little bulk (149, 150, 3). Nestling diet changed seasonally, reflecting changes in availability of invertebrate stocks. Grasshoppers increased in importance, whereas flies, moths, and spiders decreased (123). The diet reflected random choice of available prey, and did not differ from that of Saltmarsh Sparrow nestlings in same marsh (123)

At Gulf Hammock, Florida, 10 most important groups fed to nestlings comprised 85% of 552 items; remaining 15% were distributed among 47 groups. Most important (by volume): long-horned grasshoppers (Conocephalus sp., Orchelimum sp.), spiders (mainly Lycosidae), and moths (Noctuidae and Pyralidae). Among smaller insects, many homopterans, mainly Delphacidae, delivered. Except for several fiddler crabs (Uca sp.), Florida birds took few mud-inhabiting invertebrates. Nestling diets significantly more diverse in Florida than in New York; in New York, average trophic diversity (Brillouin's Hpop) was 1.08; corresponding value in Florida was 1.14 (3).

In altered (mosquito-ditched) marsh at West Gilgo, New York, food was about equally divided between prey inhabiting ground and vegetation (53% and 47%, respectively). Tabanid flies made up 71% of volume (47% immatures and 24% adults), followed by soldier flies, 10% (equally divided between adults and immatures).

In comparison to other regions, nestling diet in South Carolina (n = 280 items; 20 samples from 9 nests; WP, unpublished data) was most similar to that in New York, in that a large proportion of ground-inhabiting forms were delivered, primarily wolf spiders, which composed 16% of items, followed by larvae and pupae of flies (Stratiomyidae, Tabanidae, 10%). Among prey that was presumed to occupy vegetation, the most important were leaf hoppers (Cicadellidae and Cercopidae (51% of items) and spiders (10%). In terms of volume, however, most important were crickets (Gryllidae, 25% of volume), followed by Conocephalus grasshoppers (24%), wolf spiders (9%), and amphipods (8%).

Nest Sanitation

Both sexes remove fecal sacs from cup and rim usually dropping them > 10 m from nest. On one occasion in South Carolina, a female ate fecal sac at nest (WP). Parents do not defecate in vicinity of nest.

Cooperative Breeding

Not reported.

Brood Parasitism by Other Species

Although a Seaside Sparrow was seen feeding a fledgling Brown-headed Cowbird (Molothrus ater) on Martha's Vineyard, Massachusetts (212), interspecific brood parasitism is not yet confirmed. Seaside Sparrow is also reported to have fed Red-winged Blackbird (Agelaius phoeniceus) fledglings (213) and Saltmarsh Sparrow nestlings (WP). Brown-headed Cowbird is seldom seen in salt marshes, perhaps owing to shortage of high perches.

Fledgling Stage

Departure from the Nest

Young normally leave nest 9–11 days after hatching, but may leave on day 8 if nest is disturbed. All brood mates usually leave within several hours of each other.


Based on nestling growth data from New York (JSG, unpublished data, 1977–1978; maximum n = 39 nestlings on day 1 to n = 5 on day 11) best fit a logistic relationship (214, 215). Standard parameters for the Seaside Sparrow growth curve are the growth rate constant (K, which is the tangent to the logistic growth curve at inflection), adjusted asymptotic weight that gives the best fit to a straight line in a linearized version of the growth curve (A), and time interval for growth from 10 to 90% of the asymptotic weight (t10–t90): mean K = 0.549, A = 21.1 g, t10–t90 = 8.0 days. WP estimated K = 0.546 (163). Figure 13 shows the growth curve for Seaside Sparrow in New York.

Association with Parents or Other Young

Fed by both adults up to 20 days after fledging (176).

Ability to get Around, Feed, and Care for Self

In Florida Everglades, within 8 days one individual was able to make short, 1–2 m flights and hops (9). Fledglings 17–18 days old post-hatching are capable of making somewhat longer flights of several meters (161). At this time, a fledgling approached by predator (human) often freezes until human has moved away and then flees by running on the ground (161).

Immature Stage

Independent juveniles formed groups of 2–7 individuals, initially near nest, by early June when groups were occasionally accompanied by adults (161, 9). By late June, most older juveniles (about 30 days post-fledging) were in flocks (9). Winter home range was sometimes larger than breeding home range. Group members mobbed predators together (161). Research on radio-collared fledglings and juveniles (137, 9) indicated that post-independence flocks of older juveniles (mean flock size 4.8 ± 2.9 SD) began to range widely from June to late July and soon sought out dense patches of sawgrass (Cladium), especially by onset of molt in August and September (9). Little movement occurred in this southern subspecies in winter when they generally stayed in the taller, dense vegetation in the general breeding area, but sometimes individuals visited the margins of nearby tree islands (9). This habitat shift by juveniles from just after fledging to the time of molt in A. m. mirabilis suggests that local, small-scale variation in patch-types is an ess crucial element in the nonbreeding ecology of this species (137, 9).

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