SPECIES

Seaside Sparrow Ammospiza maritima Scientific name definitions

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

Diet and Foraging

Feeding

Main Foods Taken

Breeding period. Adult and larval insects, spiders and spider egg cases, and some amphipods, but last is not as important as in Saltmarsh Sparrow (Ammospiza caudacuta). Diet of northern populations best known from New York studies of food brought to nestlings (149, 150, 123); it is likely that adults consume the same food types, although the proportions may differ.

Overwintering period. Seeds, adult insects, spiders, decapods (crabs), amphipods, mollusks, and marine worms (Annelida) are taken at this season (125). Compared to some breeding populations, little is known in detail about nonbreeding diet in most populations. The preceding description almost certainly comes from stomach contents of specimens taken by A. T. Wayne in coastal marshes near Charleston, South Carolina, where both northern nominate birds and resident macgillivraii overwinter. Evidence from stable-isotopes (δ13C and δ15N) indicated that overwintering birds (likely local resident individuals and northern visitors) in coastal North Carolina relied on a C4 plant-based diet (i.e., primarily seeds of Spartina alterniflora (smooth cordgrass) and arthropods that consume S. alterniflora) year round; a small proportion of signatures pointed to a diet more associated with C3 plants (e.g., Salicornia, Juncus) (141) . Thus, this study indirectly supported use of tidal marsh arthropods in the winter diet, as in the breeding season. The shift to seeds of Spartina alterniflora takes place in late summer and early fall, but arthropods evidently remain an important food type during the overwintering period.

Microhabitat for Foraging

Feeds mainly in open and moderately open stands of grass in open space around bases of vegetation, shallow pools, and pannes. At Gulf Hammock, Florida, fed most frequently in Spartina alterniflora (3). In contrast, the dominant cover—black needlerush (Juncus roemerianus)—was infrequently used, probably because of low prey availability. Saltgrass (Distichlis spicata) was little used for feeding, perhaps because birds have difficulty traversing the dense matrix of stems. In contrast, glasswort (Salicornia), which had about the same prey density as saltgrass, but is more open near ground, was a frequent feeding site. Probably due to greater prey availability, much foraging was near tidal creeks, either on edges or in bordering Spartina alterniflora, or at edges of muddy pools (3). In southern Florida, A. m. mirabilis, which preferentially occupies freshwater prairie habitat dominated by Muhlenbergia grass and underlaid by hard, oolitic limestone substrate, nestlings, and adults also by necessity, depend on prey items taken from herb vegetation as soft substrates such as muds do not occur there in that habitat type (9).

In New York State, birds (n = 693 observations) foraged in shallow pools 26% of the time, compared to this microhabitat's 5% coverage of study area. The use/coverage ratio of pannes was 26/20; new-growth Spartina alterniflora: 24/57; mixed grasses (medium-height S. alterniflora and salt meadow grasses [saltgrass and Spartina patens]): 21/6; Phragmites: 2/8; wrack: 1/2; salt meadow grasses: 1/3 (123).

Food Capture and Consumption

Long, stout bill is partly adapted to probing mud; strong, large foot adapted for clinging to upright stems of grass and for running over mud (151, 152, 153, 154). Most common foraging mode is walking on ground, gleaning arthropods from surrounding vegetation, usually by attacking prey that can be reached by extending neck or by lunging short distances. Individuals walking on ground also probe and peck mud or whatever surface they are walking on. May chase elusive items. Rate of movement on ground about 2.8 m/min; average duration of stop 4.2 s (155).

Less frequently, birds forage above ground, slowly hopping or climbing through grass, gleaning as they move. Birds perched above ground also glean surrounding vegetation or snap at items in air; rarely hover or hawk flying prey. In New York, gleaning vegetation accounted for 35% of 282 observed foraging movements, whereas gleaning or probing mud was used 38% of time, gleaning wrack 11%, gleaning or probing water 10%, hovering or aerial hawking 4%, and chasing or lunging 2% (3). Food search rarely involves use of bilateral scratch (both feet employed in unison) in the field to displace fibrous litter (156), but used more often in captivity (157). In fall, often forages in loose groups that congregate in patches of tall Spartina alterniflora. Birds perch on seed heads and remove individual seeds directly from plant. Seeds also gleaned from ground. Spiders and seed-eating bugs (Lygaeidae) are captured in seed heads.

Diet

Major Food Items

Stomach contents based on data from the U.S. Fish and Wildlife Service, Office of Migratory Bird Management (hereafter, USFWS data) indicated that relatively few arthropod groups are used. For birds taken in May–October, the most important groups were fly (Diptera) larvae, adult and larval moths (Lepidoptera, primarily Noctuidae), spiders (Lysosidae, wolf spiders), bugs (Cicadellidae, leafhoppers), and Orthoptera (Acrididae, short-horned grasshoppers and Grylloidea, crickets). The composition of adult diets reported here is similar to that of nestlings in New York (158). Compared to Saltmarsh Sparrow (Ammospiza caudacuta) collected at same time in New York, few amphipods (Amphipoda, Orchestia grillus) were taken by Seaside Sparrow (see also Judd [159]), reflecting the tendency of the latter species to feed primarily in habitat dominated by Spartina alterniflora and the former to also forage in supratidal saltmeadows (S. patens and Distichlis spicata), where amphipods dominate around bases of grasses (149). Diets of the two species are similar otherwise with smaller differences in detail (123).

Quantitative Analysis

Stomachs of 6 individuals collected from late summer to early fall in New Jersey (USFWS data) had large amounts of crabs (Uca, 36% of volume) and snails (Melampus, 24%). Proportionately more seeds taken in fall and winter than in summer. Most important seeds from 13 individuals were S. alterniflora (10–25% of total plant food sample), saltbush (Atriplex, 5–10%), smartweed (Polygonum, 2–5%), and bristlegrass (Setaria, 2–5%) (160).

At Grande Isle, Louisiana (USFWS data), diet (6–9 June, n = 16) mainly Orthoptera (33% of volume), moth larvae (26%), and spiders (18%). Although items not identified to family, most were probably from standing vegetation rather than from ground.

At Cape Sable, Florida, most important food items (March–April, n = 15): beetles (35.5% of volume), spiders (14.5%), Heteroptera (bugs, 9.9%), and Hymenoptera (8.3%). Numerically most important groups were ground-inhabiting taxa such as ground beetles (Carabidae), variegated mud-loving beetles (Heteroceridae), and checkered beetles (Cleridae). Several stomachs contained amphipods and mollusk fragments. Sweep-net samples of vegetation in A. m. mirabilis nesting habitat suggested that most prey items found in stomachs are probably taken from ground rather than vegetation (161).

Food Selection and Storage

In New York, prey fed to nestlings (A. m. maritima) reflected random choice of most available items, regardless of species or size; changes in prey abundance were tracked over the nesting period (123). Food was typically delivered to nests in boluses of several different prey items, larger items masticated. There were few differences between nestling diet and food availability, or between the diets of Seaside Sparrow and Saltmarsh Sparrow nesting in the same marsh. Adults foraging for nestlings showed a significant preference for adult Lepidoptera (Noctuidae), subadult (pupae and larvae) tabanid flies (Tabanidae), subadult soldier flies (Stratiomyidae), and isopods (Isopoda). These five groups composed > 80% of dietary volume. In general, adults selected larger but less abundant prey such as flies and moths, and avoided smaller items such as plant bugs (Miridae) (123). Data on foods used during the reproductive period concern arthropod groups and some arthropods identified to species obtained by sparrows in vegetation or in mud in New York (149). Prey taken from ground or water, specifically larval tabanids and stratiomyids, for nestlings was 56% more important than that from vegetation. Yet, in comparing two seasons, most of the annual variation in nestling diets was attributable to prey from the vegetative layer, not from muddy pools (158). There is evidence from historic records on the variety of prey in adult diets that arthropod groups eaten by adults are similar to those fed to nestlings (159, USFWS data). Indeed, adults in New York were observed consuming some of the same prey types brought to nests during, as might be expected given local prey resources available (WP, JSG).

Comparable data on nestling diets and prey selection are only available for A. m. mirabilis (8, 9). Six orders of Insecta and Araneae (spiders) comprised nestling diets in this subspecies. Adults carried several prey items per trip to nests as they do in New York. Lepidoptea, Orthoptera, and Odonata (dragonflies), the last being unique in nestling diets to the south Florida population (9), were delivered selectively compared to availability. Coleoptera and Araneae, in contrast to the north, were rarely brought to nestlings, even though these groups represented 88% of available prey. Adults carried only abdomens of odonates and orthopterans to nests. Relative use of prey items changed over the course of season as in the north, and varied annually and among sites. As noted previously, Diptera and other mud-dwelling prey were absent in prey delivered to nestlings, reflecting the nature of the freshwater prairie habitats used in southern Florida.

Food storage has not been reported.

Nutrition and Energetics

Captive birds maintained on mixture of seeds (canary seeds, thistle, red and white millet); propagate in captivity while maintained on commercial soft-billed bird mixtures, supplemented by crickets (162).

Males on large activity spaces (> 8000 m2) on ditched salt marshes in New York (Long Island) may expend more energy patrolling than do those defending smaller territories (< 2000 m2) on unaltered marshes; males in ditched marshes moved (in flight and on ground) 7.7 m/min, as compared with 3.5 m/min for males in unditched marshes (116).

Neither sex appears to lose body mass as a result of energy expenditure related to parental care. Weights during breeding period (15 May–15 August) and after breeding (16 August–15 October) did not differ at Oak Beach, New York (163).

Metabolism and Temperature Regulation

Shortly after capture, a handheld A. m. nigrescens had mean cloacal temperature of 41.8°C (range 39.8–43.0, n = 6). Panting occurred when body temperature was 41.5°C (C. H. Trost, personal communication). Bill size variation appears to be at least partly related to temperature regulation in this species, which lives in relatively open habitats exposed to high radiant insolation, as an exposed body heat transfer surface to external environment (164). However, we suspect that variation in bill size and shape also reflects ecomorphological variation that is correlated with environmental trophic resources arising from selection in relation to prey size and types (e.g., 165, 166, 167) and to their probing behavior into mud for larval marsh insects (150, 158). The relative role of these two factors (trophic, physiological) on bill size and shape in salt marsh sparrows is unknown.

Drinking, Pellet-Casting, and Defecation

From Poulson (168). Can drink water with about the same salinity as seawater, but in preference tests, birds discriminated against salt solutions in favor of distilled water. After acclimation, captives maintained weight while provided ad libitum 0.4 M NaCl. During acute dehydration, 3 birds lost 2.9% of body mass/d. Acclimated birds maintained on 0.4 M NaCl regularly able to produce cloacal urine with concentrations of 450 mEq Cl-/l, a concentration 3.5 times that of their blood plasma and slightly higher than maximum of brackish water in area where birds captured.

Adults defecate on ground, apparently randomly; males also defecate from exposed perches during pauses in singing; defecation interspersed with tail-flicking.

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