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Main Foods Taken
Primarily small fishes, but also shrimp and occasionally other invertebrates; >50 fish species listed as prey (Atwood and Kelly 1984).
Microhabitat For Foraging
Variety of shallow-water habitats. On marine coasts, feeds primarily in bays, lagoons, estuaries, river and creek mouths, tidal marshes, and lakes; occasionally offshore (prevalent for S. a. browni). Inland feeding sites include rivers, streams, sloughs, dike fields, marshes, ponds, sand pits, and reservoirs. At an inland salt flat, foraged over unvegetated sand or silt—clay substrates in clear water averaging <78 cm deep (Talent and Hill 1985). On Mississippi River in Missouri, abundance and variety of forage fish greatest in water <1 m deep in main-channel and side-channel habitats immediately adjacent to sand islands, where surface water temperature, water clarity, current velocity, and substrate characteristics are unique (Tibbs 1995). Although forage densities were highest in shallow-water habitats of the Mississippi River, individuals tended to be most successful foraging in water >1 m deep (K. Dugger pers. comm.). In Oklahoma, shifted feeding sites as streams dried, selecting sites with higher densities of fish (mean 25.3 fish/m3, range 0.1–126.7, n = 36 sites) than random (mean 7.5 fish/m3, range 0–106.8, n = 36 sites; LAH)
Food Capture And Consumption
Forages throughout day. Searches for prey while flying or hovering 1–10 m above water, then quickly plunges to surface; does not fully submerge. Normally plunge-dives and grasps prey with open mandibles; rises well above water after capturing prey to manipulate and swallow food in flight (Burroughs 1966). Frequently alternates series of short dives and hovering, as if unsure of prey location. Inland, up to 35% of dives reported successful, but rate differs among habitats (Talent and Hill 1985, Wilson et al. 1993, Schweitzer 1994). Occasionally captures flying insects over land and water, or skims water surface to capture swimming insects (McDaniel and McDaniel 1963, Wilson et al. 1993) and tadpoles (JB). Occasionally captures crustaceans while standing in shallow water (Carreker 1985). Incubating birds sometimes capture insects hovering near head (Schulenberg et al. 1980, Wilson et al. 1993).
Probably any small surface-swimming, nonspiny fish 2.0–9.0 cm long with body <1.5 cm deep, as surmised from fish dropped or observed in colonies (Moseley 1976, Massey and Atwood 1980, Atwood and Kelly 1984, Wilson et al. 1993). Dropped fish may be too large to swallow, but indicate principal prey species selected; size of prey varies depending on age of chick being fed (Atwood and Kelly 1984). Common prey on Atlantic and Gulf Coasts (summarized in Carreker 1985): Massachusetts—sand lance (Ammodytes spp.), herring (Clupea spp.), and hake (Urophycis spp.); New Jersey, Florida, Louisiana—stomach contents 43% anchovy (Engraulis eurystole), 7% menhaden (Brevoortia tyrannus), 6% mummichog (Fundulus heteroclitus), 5% crustaceans, 1% silversides (Menidia spp.), and 38% unidentified items (n = 49); Mississippi and Texas—Gulf menhaden (Brevoortia patronus) and bay anchovy (Anchoa mitchilli). On California Coast: northern anchovy (Engraulis mordax), topsmelt (Atherinops affinis), jacksmelt (A. californiensis), killifish (Fundulus parvipinnis), shiner perch (Cymatogaster aggregata), and deep-body (Anchoa compressa) or slough (A. delicatissima) anchovies (Massey 1974, Atwood and Kelly 1984). Also eats various surfperch (Embiotocidae), mosquito fish (Gambusia affinis), rough silversides (Membras martinica), flat croaker (Leiostomus xanthurus), and many other species (U.S. Fish and Wildlife Service [USFWS] 1980, BCT). In interior: Platte River, NE—primarily red shiner (Notropis lutrensis), creek chub (Semotilus atromaculatus), and plains killifish (Fundulus zebrinus; Wilson et al. 1993); Salt Plains National Wildlife Refuge, OK—plains killifish, sand shiner (Notropis stramineus), plains minnow (Hybognathus placitus), Mississippi silversides (Membras beryllina), and gizzard shad (Dorosoma cepedianum; Talent and Hill 1985); Mississippi River, MO—159 fish dropped in colonies, dominated by shad (Dorosom a spp.), river carpsucker (Carpiodes carpio), and Notropis minnows (Smith and Renken 1990). River shiner (Notropis blennius) reported as major prey along Mississippi River (Hardy 1957).
Diet in S. Carolina included shrimp, marine worms, and ants (Sprunt and Chamberlain 1970: 276). Stomachs of 3 Least Terns shot in Suriname contained 34 small shrimp (Palaemon schmitti), 3–5 Sciaenidae fish, and 1 unidentified fish (Spaans 1978).
Food Selection And Storage
Takes an array of fish and aquatic invertebrates occurring in upper 15 cm of water in primary feeding areas. Appears to select for fish, especially those not deep-bodied relative to length.
Nutrition And Energetics
Metabolism And Temperature Regulation
No quantitative data. Individuals nesting in hot environments alleviate heat stress by panting, drooping wings, elevating feathers, standing in water or on saturated ground, wetting breast-feathers and then preening, and increasing frequency of parental shifts during incubation (Grant 1982, Talent and Hill 1985, Wilson et al. 1993). Chicks pant, stand in water, and seek shade under vegetation and debris; adults cool eggs and chicks by shading with body or by dripping water on them from wetted feathers.
Drinking, Pellet-Casting, And Defecation
Unclear whether species drinks water; skimming water while flying may be for drinking or for capturing invertebrates. Not reported to produce pellets. Nesting adults often dive at, mob, and defecate on human or other animal intruders in nesting territories.
Thompson, Bruce C., Jerome A. Jackson, Joannna Burger, Laura A. Hill, Eileen M. Kirsch and Jonathan L. Atwood. 1997. Least Tern (Sternula antillarum), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/290