Food Habits

Main Foods Taken

Fish and some marine invertebrates.

Microhabitat For Foraging

Primarily forages in shallow (<150 m depth) waters of estuaries and continental shelf, usually within 20 km of shore; occasionally over deeper waters of continental slope off Pacific coast, where shelf is relatively narrow (Briggs et al. 1983). Closely associated with prey-rich regions of coastal upwelling off California (Briggs et al. 1983), Panama (Spear and Ainley 1999), Galápagos Is. (Hayes and Baker 1989, Mills 1998), and Peru (P. o. thagus; Duffy 1983d). Regularly forages inland in shallow brackish and freshwater ponds and lagoons in Puerto Rico (Collazo 1985) and Aruba (Voous 1983); Lake Okeechobee, FL (Smith and Goguen 1993); and hypersaline Salton Sea, CA (Sturm 1998).

Food Capture And Consumption

Figure 2 . Captures fish mainly by surface plunging. Sights prey from air, then dives head-first from heights as great as 20 m (Murphy 1936). During dive, withdraws head over shoulders, pulls legs forward, and bends wings at wrist (Schreiber et al. 1975); also rotates body to left, probably to avoid impact injury to trachea and esophagus, which are fixed on right side of neck (Schreiber et al. 1989). As bill enters water, thrusts legs and wings backward, accelerating movement of bill toward prey. Gular pouch expands with up to 10 l of water as rami of lower mandible bow, probably due to contraction of pterygoideus ventralis medialis muscle (Burton 1977), forming an opening of about 500 cm² (Schreiber et al. 1975). Fish chased into pouch by streamlined upper mandible, which meets lower rami as they return to normal unbowed position, closing the bill and trapping fish inside pouch. If dive unsuccessful, raises head quickly with bill open to allow water to drain out immediately. If dive suc-cessful, raises head more slowly with closed bill pressed against breast to allow water to drain out, then swallows prey with a toss of the head (Orians 1969, Schreiber et al. 1975). Time required to drain pouch and swallow fish following successful dive usually <20 s (Arnqvist 1992, Shealer et al. 1997), but may be up to 1 min (Schreiber et al. 1975). Drainage time increases with dive height; greater speed of impact from high dive results in deeper penetration below surface and greater volume of water filling pouch (Arnqvist 1992). Extensive superficial air cavities on ventral surface of body provide cushion-ing upon impact with water and prevent complete submergence (Richardson 1939). Depth at which prey can be reached limited to upper 1–2 m of water column (Duffy 1980b). Visual acuity underwater prob-ably poor because cornea cannot compensate for refraction in water (Sivak et al. 1977).

Adults more skillful plunge-divers than immatures; e.g., percentage of successful dives, adults versus immatures: 84% (n = 905) versus 75% (n = 1,544) in sw. Mexico (Schnell et al. 1983); 83% (n = 206) versus 49% (n = 436) in Belize (Brandt 1984); 73% (n = 258) versus 58% (n = 115) in U.S. Virgin Is. (Collazo 1985); 70% (n = 882) versus 56% (n = 441) in sw. Puerto Rico (Shealer et al. 1997). In e. Florida, success improved linearly with age (determined by plumage): first-year birds, 4% (n = 86); juveniles (12–22 mo), 8% (n = 381); sub-adults (22 to <40 mo), 12% (n = 121); adults (>36 mo), 14% (n = 382; Carl 1987). Greater success of older birds attributed to their use of (1) greater dive heights (6–18 m), which increase air speed and depth of penetration below surface, potentially allowing more prey to be reached, and (2) steeper dive angles (>60°), which re-duce aiming errors caused by refraction and increase probability of encountering targeted prey within sampled water column (Carl 1987). Adults also appear better able to evaluate chance of success and abort attempt if probability too low; often wheel in air as if about to dive, then resume searching flight; immatures do not wheel without completing dive (Coblentz 1986).

Brown Pelican occasionally forages while sitting on water by surface-seizing, similar to white pelican species (Haverschmidt 1949, Dinsmore 1974); Peruvian Pelican commonly employs surface-seizing (Murphy 1936, Duffy 1983d). Surface-seizing used when dense school of fish is close to surface within easy reach (Murphy 1936), when water is too shallow and muddy for plunge-diving (Haverschmidt 1949), and when pirating food from another species or scavenging offal (Sefton 1950; Duffy 1980a, 1983d).

Forages most often in early morning and evening and on rising tides (Palmer 1962, Schnell et al. 1983, Carroll and Cramer 1985). Usually faces downwind and away from sun when diving (Carl 1987). Brown Pelican occasionally forages at night (Robert and McNeil 1989); Peruvian Pelican regularly does so (Duffy 1980a). Frequently forages in mixed-species flocks over schools of fish; may act as catalyst for flock formation because conspicuous plunge-diving behavior attracts other seabirds to area (Briggs et al. 1987, Mills 1998). Regularly exploits feeding activities of other species to access prey. Frequently forages with Galápagos Penguin (Spheniscus mendiculus), which often dives below school and feeds on fish on way up to surface, driving fish within pelican’s reach (Mills 1998). Peruvian Pelican robs fish from other seabirds, mainly the deeper-diving Peruvian Booby (Sula variegata) and Guanay Cormorant (Phalacrocorax bougainvillii), allowing pelican to access prey occurring beyond its own reach (Duffy 1980b). Brown Pelican observed stealing fish from Great Blue Heron (Ardea herodias) in Georgia (Bildstein 1980) and following foraging Wood Storks (Mycteria americana) in Florida, seizing prey stirred up by them (Rodgers 1978). Frequently follows fishing boats to feed on by-catch; regularly visits marinas and fishing piers to feed on offal after catch has been cleaned (Lincer et al. 1979).

Vulnerable to kleptoparasitism while draining gular pouch prior to swallowing prey. Kleptoparasites include gulls (Laughing [Larus atricillus; Schnell et al. 1983, Carroll and Cramer 1985, Shealer et al. 1997], Heermann’s [L. heermanni; Tershey et al. 1990], Band-tailed [L. belcheri; Duffy 1980b], Kelp [L. dominicanus], Gray [L. modestus; Forbes 1914]) and terns (Roseate [Sterna dougallii], Sandwich [S. sandvicensis; Shealer et al. 1997]). Gulls steal fish from pelican’s bill while perched on its head or back or while hovering near its head, or plunge into water to capture fish escaping from pouch; terns usually employ latter technique (Carroll and Cramer 1985, Shealer et al. 1997). Kleptoparasites generally target successful pelicans regardless of age (Schnell et al. 1983, Shealer et al. 1997); since adults more successful foragers than immatures (see above), adults more often targeted (Tershey et al. 1990, but see Carroll and Cramer 1985). Heermann’s Gulls in Gulf of California attempted to kleptoparasitize 13% (n = 721) of all pelican dives (Tershey et al. 1990); Laughing Gulls attempted to steal fish on 67 % (n = 2,449) to 87% (n = 472) of dives in sw. Mexico (Schnell et al. 1983, Carroll and Cramer 1985). Laughing Gulls and Sandwich and Roseate terns attempted to kleptoparasitize 55% (n = 1,323) of dives in sw. Puerto Rico; successfully stole fish on 15% of attempts (Shealer et al. 1997).

Major Food Items

Small, surface-schooling fishes make up bulk of diet throughout range. Along Atlantic and Gulf coasts of U.S., menhaden (Brevoortia spp.) usually predominate; mullet (Mugil spp.) also important (Palmer 1962, Blus et al. 1979b, Fogarty et al. 1981). Off Yucatán Peninsula, anchovies (Anchoa spp.), herring (Opisthonema spp.), and sailfin mollies (Poecilia velifera) consumed (Blankinship 1987). In the Caribbean, dwarf herring (Jenkinsia lamprotaenia), anchovies (Anchoa and Engraulis spp.), and sardines (Sardinella and Harengula spp.) most common prey (Voous 1983, Collazo 1985). Tilapia spp. locally important at lagoons and impoundments in Aruba (Voous 1983) and Puerto Rico (Collazo 1985). Along Pacific coast, pelicans highly dependent upon anchovies; northern anchovy (Engraulis mordax) in California and Mexico (Anderson et al. 1980, 1982) and anchoveta (E. ringens) in Peru (Coker 1920, Duffy 1983d). Pacific sardines (Sardinops sagax) equally important to anchovies in S. California Bight since 1993 (F. Gress pers. comm.). Pacific sardines also eaten in Galápagos Is. (Mills 1998). Over 40 spe-cies of fishes and invertebrates consumed in Gulf of California; no one species dominant (U.S. Fish Wildl. Serv. 1983).

Quantitative Analysis

Thirty-two stomachs of pelicans from U.S. Gulf coast contained 95.8% menhaden, 3.1% silversides (Menidia spp.), 0.8% dolphin (Coryphaena spp.), and 0.3% prawns (method for quan-tifying amounts not specified; Palmer 1962). Stomachs of 3 birds collected in Puerto Rico contained average of 109 fish; 62% dwarf herring (mean weight 1.8 g, mean total length 6.0 cm) and 38% sardines (Harengula jaguana; mean weight 2.5 g, mean total length 6.8 cm; Collazo 1985). Most quantitative studies based on re-gurgitations of nestlings (see Breeding: young birds, below). Diets of adults and nestlings generally similar (Collazo 1985).

Selects prey opportunistically. Dives for an individual fish even if it is in a school (Schreiber et al. 1975). Does not carry food in pouch. Does not cache food.

No quantitative data on food intake of wild birds. Captive nestlings held in cage indoors at about 22°C consumed average of 585–679 g fish/d (18.7–29% of body mass) during growth to maximum mass, and 464–549 g/d (16.1–17.3% of body mass) while maintaining this mass (Schreiber 1976a). About 50 kg fish required to raise nestling from hatching to fledging. Captive adult consumed average of 590 g fish/d, or 17.5% of daily body mass. Food requirements of wild birds probably greater because of higher activity levels and cost of thermoregulation (Schreiber 1976a). Twenty-three captive immatures and adults kept in outdoor pen in Florida consumed about 0.5 kg fish/d; amount varied from 0.3 kg/d during summer to >0.8 kg/d on some winter days (Wolf et al. 1985). Energy expenditure of 6-kg Peruvian Pelican estimated at 2,590–3,391 kJ/d (Laugksch and Duffy 1984).

Basal metabolic rate of 3 adults (mean mass 3,038 g) averaged 896 kJ/d (Ellis and Gabrielsen 2002). No direct measures of field metabolic rate available. Resting metabolic rate of hatchling 1,060 ml O2/d (Klaassen and Drent 1991). Pants and gular-flutters for evaporative cooling. Rate and amplitude of panting increase rapidly with rising body temperature. Rate of gular-fluttering 230–290/min; independent of am-bient and body temperatures (Bartholomew et al. 1968). On hot, calm days, may orient one partially spread wing perpendicular to sun’s rays, perhaps allowing air to circulate under wing for cooling or to shade feet. Moistens and cools gular pouch by plunging opened bill into water; most commonly performed during hottest part of calm, sunny day (Schreiber 1977a).

Drinks seawater using Bill-plunge (Schreiber 1977a). Ingested salt excreted by paired salt glands located in shallow depressions in roofs of orbits anterior to eyes (Schmidt-Nielsen and Fange 1958). Glands 2.6–3 cm long and 0.6–0.8 cm wide; taper anteriorly to form ducts 1 cm long that open into narrow cavity behind external nares. Clear, salty fluid exits nares, runs down grooves on upper mandible, drips off tip (Schmidt-Nielsen and Fange 1958). Not known to cast pellets. Defecates indiscriminately in roosting and loafing areas and within breeding colonies. Guano rich in nitrogen and phosphorus; commercially harvested in Peru (Coker 1920, Duffy 1994).