Food Habits

Main Foods Taken

Primarily small (1–10 cm length) fish, some arthropods (McNicholl 1971, 1984; Salt and Willard 1971; Reed 1985; Fraser 1994a, 1994b, 1997).

Microhabitat For Foraging

In marshes, lakes, water channels and in shallow, saltwater estuaries and coastal areas. Forages throughout marshes in which they breed (MKM); in saltwater coastal areas, forages in shallow water (<1 m) over flood-tide mudflats or in areas of calm water offering high visibility (Salt and Willard 1971, Baltz et al. 1979). Fish caught to depth of 30 cm (Salt and Willard 1971).

Food Capture And Consumption

While foraging, flies back and forth over water with bill pointing downward and feet folded against body, typically about 6–8 m above water, and either plunges directly into water towards prey or hovers briefly (3–4 s) before diving (Salt and Willard 1971, Reed 1985). Plunges typically shallow with only bill and part of head submerged (McNicholl 1971), but sometimes whole body completely submerged (Dawson and Bowles 1909). Sometimes forages from perches such as posts, bridges, telephone wires, or floating boards (McNicholl 1971). Of 1,538 dives observed at shallow, salt-evaporation pond near San Francisco Bay, CA, 24% resulted in capture of a fish (Salt and Willard 1971). Small fish (those fish ≤1 cm in length) often swallowed as tern regained foraging height; larger fish (3–5+ cm in length) may be dropped from 20 m height and recaught at 10 m; this behavior repeated 3–4 times and may be necessary part of food processing (Salt and Willard 1971).

No record of kleptoparasitism.

Most information on diet anecdotal or based on casual observations. Analysis of stomach contents of 15 individuals collected in Jul in Monterey Co., CA, identified 64 prey items, primarily shiner perch (Cymatogaster aggregata; n = 27, young of the year, estimated standard length 35 mm), northern anchovy (Engraulis mordax; n = 21 juveniles), and arrow goby (Clevelandia ios; n = 8 adults; Baltz et al. 1979).

For 166 courtship feedings observed in Todd and Douglas Cos., MN (Fraser 1997), fish presented included 65 yellow perch (Perca flavescens), 25 shiners (Notropis sp.), 13 sunfish (Centrarchidae), and 5 northern pike (Esox lucius); at this same location, 148 prey items brought to chicks included 79 yellow perch, 24 shiners, and 8 stickleback (Gosterosteidae).

In Minnesota, sizes of fish brought to mates (for courtship-feeding) averaged larger than sizes of fish seined nearby; size of prey fed to chicks increased as chicks grew; 1-wk-old chicks fed fish about 3.3 cm long, older chicks received fish 5.2 cm long (Fraser 1994a, 1997; M. C. Coulter unpubl.). Not known to store food.

No information on nutrition. Estimates of energy intake and expenditure of foraging terns based on standard formulas provided by Reed (1985; see Metabolism and temperature regulation, below).

Standard metabolic rate (SMR) estimated (by formula) as 3.6 kJ/h; for perching, energy needs 1.6 × SMR; for flight and gliding, 4 × SMR; energy obtained from typical prey (6 cm Atlantic silverside [Menidia menidia]) about 7.7 kJ/fish (Reed 1985).

No information.