Breeding

Pair Formation; Nest-Building

Male selects nest site and advertises for mate, which he usually obtains in 2–4 d (range 1–21). Nest-building, an integral part of early courtship, begins once female occupies male’s territory. Usually requires 7–10 d to complete (Schreiber 1977a).

First/Only Brood Per Season

Figure. 3 . Breeds annually in spring-summer above 30°N, annually in winter-spring between 20 and 30°N, and irregularly throughout year on 8.5- to 10-mo cycle below 20°N. Availability of sufficient food has major influence on timing of breeding. Onset of breeding in Bay of Panama coincides with start of seasonal upwelling period (Montgomery and Martínez 1984). Breeding in S. California Bight begins when anchovies become abundant near breeding colonies (Anderson et al. 1982, Anderson and Gress 1983). Some Pacific coast populations forgo breeding during strong ENSO events (Valle et al. 1987, Tovar et al. 1987). Along Atlantic and Gulf coasts of U.S., breeding inhibited by freezing temperatures (Schreiber 1980a), which reduce prey availability and have direct physiological effects on pelicans (see Demography and populations: causes of mortality, below). Breeding requires about 18 wk to complete: 1–2 wk for courtship and nest-building, 4.5 wk for incubation, 10–12 wk for nestling stage (Schreiber 1979). Egg-laying dates: Maryland, late May–early Sep, peak Jun 1987–1991, but peak Apr–May 1999–2000 (D. Brinker pers. comm.); N. Carolina, mid-Mar to Jul, peak Apr–May (Parnell and Soots 1982, MAS); Florida Atlantic coast, Dec–Jun; Florida Keys, irregular, peak Feb–Apr; Florida Gulf coast, Jan–Jun, peak Mar–May (Schreiber 1980a); Louisiana, Mar–Jun prior to extirpation (Blus et al. 1979a, Schreiber 1980a); phenology after reintroduction (see Conservation and management: management, below) follows that of source populations from Florida’s Atlantic and Gulf coasts (Blus et al. 1979a, McNease et al. 1984); Texas, Mar–Jun, peak Apr–May (Schreiber 1980a, King et al. 1985); S. California Bight, Dec–early Aug, peak usually Feb–May (Anderson and Gress 1983); Gulf of California, Nov–May (D. Anderson pers. comm.); Panama, Jan–May on most islands, Jun on Isla Iguana (Montgomery and Martínez 1984, Butler et al. 1998); Galápagos Is., year-round (Harris 1969); Aruba, May–Nov (Voous 1983). Breeding begins May–Aug in w. and sw. Puerto Rico; breeds throughout year (peak Sep–Nov) in e. Puerto Rico and U.S. Virgin Is. (Collazo 1985). Breeding season in Venezuela Nov–Jun, peak Jan–Feb (Guzman and Schreiber 1987). Peruvian Pelican breeds mainly Nov–Apr (Forbes 1914, Coker 1920).

Selection Process

Male selects site and performs Head Swaying display to attract female, which he allows to land nearby and eventually occupy nest site (Schreiber 1977a). In tree colonies, presence of nearby perches appears critical to site selection; perches used when taking off, landing, preening, sleeping, and feeding nestlings (Schreiber 1977a). Mated Peruvian Pelican pair arrives overnight and occupies site, sometimes usurping nest of Guanay Cormorant or Peruvian Booby (Duffy 1983a).

Microhabitat; Site Characteristics

Variable. Nests mainly on ground along Atlantic and Gulf coasts of U.S. (excluding Florida) and in s. California, Baja California, and n. Gulf of California. Mostly nests in trees in remainder of range. Ground nests along Atlantic and Gulf coasts sometimes built directly on bare sand or shell, but more typically in dense stands of herbaceous plants or low shrubs (Williams 1989, Parnell and Shields 1990, McNease et al. 1992). Vegetation usually open enough to provide space around nest for parents to land and take off, as well as preen and loaf while not on nest. On islands subject to tidal flooding, older breeders tend to select higher sites than younger, inexperienced breeders do (Blus and Keahey 1978). Ground nests along Pacific coast and in Gulf of California built on steep, rocky slopes, in canyons, or on ridges (U.S. Fish Wildl. Serv. 1983). Tree nests usually placed in or near top of vegetation to provide easy access. Height of nest above ground varies from 0.5 to 30 m (Montgomery and Martínez 1984, Collazo 1985). Mangrove (Avicennia, Rhizophora, Laguncularia) most common substrate for tree nests in Florida (Nesbitt 1996), the Caribbean (Collazo 1985, Guzman and Schreiber 1987), west coast of mainland Mexico (U.S. Fish Wildl. Serv. 1983), and Galápagos Is. (Gifford 1913). Deciduous woodlands used in Costa Rica (Schreiber and McCoy 1983), Panama (Bartholomew and Goldstein 1984, Montgomery and Martínez 1984), and U.S. Virgin Is. (Collazo 1985). Also nests in low littoral vegetation in U.S. Virgin Is. and Conejo Cay, Puerto Rico (Schreiber et al. 1981, Collazo 1985) and humid forests and tropical thorn woodlands in Venezuela (Guzman and Schreiber 1987). Nests on low (1–2 m) wooden nesting platforms erected on dredge-spoil island in St. Andrews Bay, FL (Wood et al. 1995). Peruvian Pelican nests only on the ground; selects level area (mean slope 2° ± 2 SD; n = 20) with bare substrate (Duffy 1983a).

Construction Process

Female builds nest using material gathered by male, who supplies progressively smaller sticks as construction continues. Sticks arranged and pushed into place with bill, nest cup formed by treading with feet and pushing down with body. Male rearranges material while at nest. Nest may be completed in as little as 4 d, but usually 7–10 d required (Schreiber 1977a).

Structure And Composition Matter

Variable, reflects availability of material at colony site. Ground nests range from shallow depression in sand lined with grasses to bulky structure of sticks, grass stems, or seaweed; tree nests generally well-built platforms of sticks lined with grasses or leaves. On Virginia barrier island, nests constructed of marsh elder (Iva frutescens), cordgrass (Spartina sp.), and sea rocket (Cakile edentula) stems (Williams 1989). Most nests in Florida built from mangrove stems and lined with grasses and leaves (Schreiber 1977a). In Louisiana, stems of black mangrove (Avicennia nitida), sea matrimony (Lycium carolinianium), sea purslane (Sesuvium sp.), and grasses (Phragmites communis, Spartina alterniflora) used, along with pieces of plastic, rope, fishing line, window screen, and other human-made materials (McNease et al. 1984). Kelp commonly used in S. California Bight (Western Foundation of Vertebrate Zoology [WFVZ] data). Males often take material from unattended nests (Schreiber 1977a).

Dimensions

Variable, depending on substrate and availability of material. Five ground nests on S. Carolina barrier island had mean outside diameter of 18 cm (range 15–30), mean inside diameter of 15 cm (range 13–25), mean outside height of 11 cm (range 8–13), and mean inside depth of 7 cm (range 5–8; WFVZ data). In Louisiana, outside diameter averaged 64–76 cm, height 22 cm, inside diameter 27–30 cm, and depth 9 cm (n not given; McNease et al. 1984).

Microclimate

Little information. Most nests built on open ground or in treetops, fully exposed to the elements. Mean temperature of Peruvian Pelican nest rim 29.2°C ± 0.3 SE (n = 18) when ambient air temperature 24–26°C (Duffy 1983a).

Maintenance Or Reuse Of Nests, Alternate Nests

Male brings new material throughout incubation and nestling stages, which female adds to nest. In Florida mangrove colonies, nestlings gradually dismantle nest so that little remains by the time they fledge; consequently, new nests must be built each year (Schreiber 1977a, Ploger 1992). In Galápagos Is., where breeding may occur on 9-mo cycle (Harris 1969), some nests used twice within 1 yr (Gifford 1913, Boersma 1977); not known if second use by same pair as first. Ground nests on xeric islands in S. California Bight occasionally reused or rebuilt in subsequent years (U.S. Fish Wildl. Serv. 1983).

Nonbreeding Nests

During an 8-yr period in Florida, 18 of 346 (5.2%) fully constructed nests did not receive an egg; several other nests started, but not completed (Schreiber 1979). Twenty-five of 395 (6.3%) nests started did not receive an egg during a 3-yr study in N. Carolina (MAS).

Shape

Subelliptical (n = 345), oval (n = 335; Anderson and Hickey 1970), long subelliptical (n = 20; Palmer 1962). Radii of curvature at ends 17.03 ± 1.77 SD and 11.55 ± 1.34 SD; elongation 1.50 ± 0.086 SD; bicone–0.136; asymmetry +0.166 (n = 20; Palmer 1962).

Size

Varies among subspecies in relation to body size (Anderson and Hickey 1970). Data reported as mean length × mean breadth in mm.

P. o. occidentalis: Cuba, 72.3 (range 75.0–68.4) × 45.9 (range 44.8–47.4, n = 6); Puerto Rico, 73.0 ± 3.6 SD (range 67.1–80.0) × 45.4 ± 3.0 SD (range 33.2–47.9, n = 18; Schreiber et al. 1981).

P. o. carolinensis: N. Carolina, 76.4 ± 3.2 SD (range 67.1–85.7) × 50.0 ± 1.5 SD (range 43.1–54.7, n = 850; MAS); S. Carolina, 75.6 × 49.7 (n = 693; Blus et al. 1997); Florida, 75 ± 3.3 SD × 50 ± 1.3 SD (n = 20; Palmer 1962), 75.5 × 48.7 (n = 51), runt egg 50.5 × 38.8 (Schreiber 1975b), 75.2 × 49.5 (n = 451; Blus et al. 1997); Panama, 74.8 ± 2.1 SD (range 68.1–79.0) × 48.8 ± 1.2 SD (range 46.5–51, n = 38; Bartholomew and Goldstein 1984), 74.4 (range 72.2–76.8) × 50.2 (range 48.8–51.4, n = 10; Wetmore 1965).

P. o. californicus: Unspecified locations: 78.5 (range 69–85) × 50.6 (range 47–54, n = 48; Bent 1922); s. Cali-fornia and Baja California: 77.7 ± 2.4 SD (range 71.3–81.8) × 50.0 ± 1.5 SD (range 47.5–54.9, n = 36; WFVZ data).

P. o. urinator: Galápagos Is.: 77.4 ± 3.7 SD (range 72–83.5) × 51.9 ± 0.9 SD (range 50.5–53.5, n = 12; calculated from data in Rothschild and Hartert 1899, 1903).

P. o. murphyi: No data.

Mean calculated volume of P. o. carolinensis eggs 90.3 ml ± 4.9 SD (range 79.4–99.6, n = 38) in Panama (Bartholomew and Goldstein 1984) and 97.4 ml ± 7.4 SD (range 66.7–125.6, n = 850) in N. Carolina (MAS). Volume of second egg averages 2% larger than others in clutch of P. o. carolinensis (Shields 2000).

Mass

P. o. carolinensis: Mean fresh egg mass in N. Carolina, 103.2 g ± 7.5 SD (range 78.9–123.6, n = 597; MAS), and in Florida, 97.8 g (n = 51; Schreiber 1975b). Mean mass of 6 eggs collected during first 3 wk of incubation in Florida 92.1 g ± 8.0 SD (range 77.6–101.5; Lawrence and Schreiber 1974). Mass of 38 eggs collected during first half of incubation period in Panama averaged 93.8 g ± 6.2 SD (range 80.6–104.6; Bartholomew and Goldstein 1984). Specific gravity on day of laying 1.06 g/ml ± 0.02 SD (range 0.98–1.13, n = 597); declines linearly over incubation period due to water loss (MAS). P. o. californicus: Mean fresh mass 110.3 g (range 97.1–124.7, n = 21; Hanna 1924) and 110.5 g (n = 10; Hoyt 1979). No data for P. o. occidentalis, P. o. urinator, or P. o. murphyi .

Mass of whole egg about 3.5% of adult female body mass (Schreiber 1979). For fresh egg components (percentage, mean wet mass), see Lawrence and Schreiber 1974, Bartholomew and Goldstein 1984 .

Color; Surface Texture

Bright chalky white with granular surface, often streaked with blood, when first laid; become smooth and stained by nest, parents’ feet, and guano during incubation (Bent 1922, Palmer 1962, MAS).

Eggshell Thickness

Varies among subspecies in relation to egg and body size. All sizes in mm. Pre-1943 (i.e., pre-DDT) mean (95% confidence limits; Anderson and Hickey 1970): P. o. occidentalis: West Indies, 0.510 (0.479–0.541, n = 6); P. o. carolinensis: S. Carolina, 0.557 (0.536–0.578, n = 23); Florida and Georgia, 0.557 (0.553–0.561, n = 172); Louisiana, 0.554 (0.540–0.568, n = 24); Texas, 0.557 (0.545–0.569, n = 43); P. o. californicus: s. California, 0.579 (0.565–0.593, n = 28); Baja California, 0.569 (0.561–0.577, n = 83). No data for P. o. urinator, P. o. murphyi, or P. o. thagus .

Significant thinning, correlated with residues of DDE, a metabolite of DDT (see Conservation and management: effects of human activity, below), reported in 1960s and 1970s throughout U.S. range (summarized in Schreiber 1980b) and in nw. Baja California (Jehl 1973). Shells ≥20% thinner than pre-1943 mean usu-ally broke during laying or early incubation (Schreiber and Risebrough 1972, Jehl 1973). As concentration of DDT in marine environment began to decline during the 1970s, eggshell thickness increased but remained below pre-1943 levels.

Most severe thinning (31–51% of pre-1943 mean) occurred in P. o. californicus in S. California Bight in 1969 and 1970; some shell-less eggs laid, many thin-shelled eggs broke during incubation, few young fledged (Risebrough et al. 1971, Jehl 1973). Mean thickness (95% confidence limits) of eggs found intact at Anacapa and Santa Cruz Is., CA, was 0.402 mm (0.383–0.42, n = 12) in 1969 and 0.393 mm (0.372–0.414, n = 16) in 1970; shells of eggs found crushed or broken averaged 0.288 mm (0.272–0.304, n = 53) in 1969 and 0.286 mm (0.272–0.300, n =72) in 1970 (Anderson et al. 1975). At Los Coronados (South I.), Mexico, mean thickness (intact, crushed, and broken eggs combined) was 0.308 mm (range 0.17–0.44, n = 48) in 1969 and 0.303 mm (range 0.18–0.44, n = 17) in 1970 (Jehl 1973). Eggshells from S. California Bight were thicker in 1971–1975 (yearly means 0.460–0.510 mm for intact eggs; 0.294–0.378 mm for crushed or broken eggs) and reproductive success improved, but shells still significantly thinner than pre-1943 levels (Anderson et al. 1975, 1977b). Mean thickness of intact eggs in-creased by about 23% between mid-1970s and mid-1980s, then stabilized at about 5% thinner than pre-1943 mean between 1986 and 1993 (Gress 1995). In Gulf of California, where DDT residues were much lower than in S. California Bight, thickness of intact eggs in 1969 averaged 0.55 mm (range 0.46–0.63, n = 39), only slightly thinner than normal (Keith et al. 1971).

In S. Carolina, eggshell thinning between 1969 and 1974 (yearly means 0.461–0.480 mm; 14–17% thinner than pre-1943 mean) impaired reproductive success of P. o. carolinensis (Blus et al. 1974a, 1974b, 1979b). Between 1975 and 1980, mean thickness increased to 0.499–0.527 mm (5–10% thinner than pre-1943 mean; Blus et al. 1979b, 1997), coincident with increases in breeding population and reproductive success (Mendenhall and Prouty 1978, Blus 1982).

In Texas, thinning of 20% (based on shell weight) in 1951 and 15% in 1961 (mean thickness 0.473 mm, n = 6) associated with population decline and low reproductive success (King et al. 1977b). However, no adverse effect on reproduction noted between 1970 and 1981, when mean thickness (0.48–0.54 mm) was only 4–14% thinner than pre-1943 mean (King et al. 1985).

In Louisiana, mean thickness between 1971 and 1976 ranged from 0.479 to 0.517 mm; this 7–14% thinning relative to pre-1943 mean had no apparent effect on reproductive success (Blus et al. 1979a).

Less severe thinning (6–8% of pre-1943 mean) observed in Florida; means in 1969, 1970, and 1974 were 0.516 mm ± 0.005 SE (n = 89), 0.511 mm ± 0.004 SE (n = 144), and 0.521 mm ± 0.004 SE (n = 122), respectively (Blus et al. 1979b). At Tampa Bay, mean thickness (95% confidence limits) increased from 0.506 mm (0.484–0.528, n = 14) in 1969 to 0.545 mm (0.508–0.582, n = 31) in 1976 (Schreiber 1977b). In 1979, means along Florida Gulf coast, Atlantic coast, and Keys were 0.527 mm (n = 37), 0.537 (n = 37), and 0.544 mm (n =18), respectively (Blus et al. 1997). Eggshell thinning had no observable effect on population stability in Florida (Schreiber and Risebrough 1972).

Mean thickness of P. o. occidentalis eggshells from Puerto Rico and U.S. Virgin Is. 0.496 mm (n = 26) in 1980–1982 and 0.526 mm (n = 20) in 1992–1993; both means within 95% confidence limits of pre-1943 mean (Collazo et al. 1998).

Clutch Size

Normal clutch for adults is 3 eggs (range 2–4); immatures, 2 eggs (range 1–3). See Demography and populations: measures of breeding activity, below.

Egg-Laying

First egg usually laid 1–3 d after nest completed. Eggs laid in early morning (before 10:00) at 24- to 64-h intervals (Schreiber 1977a); mean interval 2.0 d ± 0.2 SD (n = 257); distribution of laying intervals: 1 d, n = 1; 2 d, n = 245; 3 d, n = 11 (Shields 1998). Captives have laid 1–2 replacement clutches/season following loss of eggs or young nestlings (Dooley and Heyland 1969, Nesbitt et al. 1980). Laying of replacement clutches in the wild not verified by studies of marked individuals, but entire colonies in Louisiana have renested up to 5 times in a season following flooding (McNease et al. 1984); probably the same individuals involved. Laying of replacement clutch sometimes inferred from appearance of new eggs in nest that previously lost its clutch (Jehl 1973, Schreiber 1979). This method may overestimate incidence of re-laying because adults sometimes take over another pair’s nest, eject the eggs, and lay their own clutch (Ploger 1992). Clutches of ≥5 eggs probably the result of intraspecific egg-dumping (Pearson 1921, Bent 1922), but no direct observations.

Onset Of Broodiness And Incubation In Relation To Laying

Incubation begins with laying of first egg (Schreiber 1977b, Shields 1998).

Incubation Patch

None. Parent incubates eggs under webs of totipalmate feet (Schreiber 1977a).

Incubation Period

Ranges from 29 to 32 d in P. o. californicus; little intraclutch variation (Pinson and Drummond 1993). Incubation period of P. o. carolinensis in N. Carolina 30–35.5 d (MAS); decreases with laying order: first egg, mean 32.2 d ± 0.7 SD; second egg, 31.3 d ± 0.6 SD; third egg, 31.0 d ± 0.6 SD (n = 95 clutches; Shields 1998).

Parental Behavior

Parents share incubation duties. One parent on nest at all times; off-duty bird, when not foraging, spends most time sleeping, preening, or loafing nearby (Schreiber 1977a). In Gulf of California, nest relief normally occurs once every 1–2 d, less often when food availability low (Keith 1978). Frequency of nest relief elsewhere not quantified. During first half of incubation, nest relief characterized by much posturing between partners. Bird on nest usually performs Bowing, Head Swaying, and/or Head Turning, while arriving bird responds with Head Turning, Upright, and/or Head Swaying. Preening, Glottis Exposure, and Bill Throw often interspersed with these behaviors. During last half of incubation, little response elicited by arrival of mate. Throughout incubation, departure of relieved parent not accompanied by observable response by mate. Incubating parent periodically pushes down with 1 wing to lift body while repositioning feet on eggs, a maneuver called the Incubation Roll (Schreiber 1977a). On desert islands in Gulf of California, parent commonly returns to nest wet from bathing or carrying wet seaweed, apparently to help cool eggs (D. Anderson pers. comm.).

Hardiness Of Eggs Against Temperature Stress; Effect Of Egg Neglect

Experimental exposure to ambient temperatures during laying period resulted in significant reduction in hatching success in N. Carolina colony (Shields 1998). Eggs normally not unattended unless parent disturbed.

Preliminary Events And Vocalizations

Embryonic vocalizations, heard at close range or felt as vibrations when egg held, begin 2 d before egg hatches and several hours before external pipping (Shields 1998, 2000).

Shell-Breaking And Emergence

Chick uses egg tooth to pip hole in broadest part of egg, then rotates within egg while cutting shell widthwise until cap removed; emerges about 31 h after start of external pipping (Shields 2000). Two-thirds of 270 eggs in N. Carolina colony estimated to have hatched between 22:00 and 10:00 (MAS). Eggs generally hatch in order of laying, with first eggs hatching 25 h ± 14 SD (range –4 to 52) before second eggs, and second eggs hatching 40 h ± 13 SD (range 8–85) before third eggs (n = 90 clutches; Shields 2000).

Parental Assistance And Disposal Of Eggshells

Parents not known to assist with hatching. Eggshells sometimes crushed in nest; more often shells found outside nest, apparently tossed out by parents (MAS).

Condition At Hatching

Altricial. Body pink and naked, except for neossoptiles along posterior margin of manus; eyes open but nictitating membrane not responsive; egg tooth present. Lies prone in nest, unable to hold head upright; calls extensively (Schreiber 1976a). Mean mass of P. o. carolinensis hatchling 73.5 g ± 6.5 SD (range 54.9–87.0, n = 40; MAS), of which about 10 g is yolk retained in abdominal cavity (Bartholomew and Goldstein 1984). Hatchling mass (HM; g) can be estimated from fresh egg mass (EM; g) and egg volume (V; ml) as follows: HM = 0.8 EM – 6.5 (n = 23; r ²= 0.93; MAS) and HM = 0.8 V – 3.2 (n = 40; r 2 = 0.93; Shields 2000). Mean culmen length 21 mm ± 0.7 SD (range 19–23, n = 501; MAS). Manus length 19–22 mm; tarsus length 20–22 mm (Schreiber 1976a).

Growth And Development

First-hatched nestling grows faster than siblings (Schreiber 1976a, Pinson and Drummond 1993, Shields 1998). Mass gain most rapid during first 3 wk (Schreiber 1976a). Growth constant (K) 0.071; asymptotic mass 4,000 g (Ricklefs 1973), reached by about 50 d. Mass at independence often exceeds adult mass; stored energy aids survival as fledgling learns to forage for itself (Schreiber 1976a). Mass of 25 fledglings from 1-chick broods of P. o. californicus averaged 3,659 g ± 304 SD, mass of 21 first-hatched and 4 second-hatched fledglings in 2-chick broods averaged 3,535 g ± 426 SD and 3,242 g ± 188 SD, respectively (Pinson and Drummond 1993).

Growth of culmen rapid and linear from 4 to 5 d to fledging; growth to adult length continues after fledging (Schreiber 1976a). For P. o. carolinensis nestlings <10 d old, age can be estimated from culmen length (C) by the formula: Age = 13.79 ln C – 41.52 (n = 63; r ²= 0.94); after 10 d, culmen lengths of siblings diverge, making age determination unreliable (Ploger 1992). Tarsus grows to adult length within 30 d; wing growth slow during first 3 wk, then increases at near-constant rate through fledging; adult wing length usually not reached prior to fledging (Schreiber 1976a). Mean culmen and ulna lengths of 25 P. o. californicus fledglings from 1-chick broods, 297 mm ± 9 SD and 353 mm ± 10 SD, respectively. Means of 21 first-hatched and 4 second-hatched fledglings in 2-chick broods: culmen, 293 mm ± 15 SD and 294 mm ± 2 SD, respectively; ulna, 342 mm ± 14 SD and 339 mm ± 8 SD, respectively (Pinson and Drummond 1993).

Skin purplish pink at 2–4 d, becoming purple 5–6 d after hatching. Egg tooth reduced in size by 5–6 d, gone by 8–10 d. White down first appears on rump at 10–12 d, covers body by 21–25 d. Juvenal plumage gradually replaces down, with scapulars emerging first at 30–32 d. By 62–65 d, down remains only on lower neck, middle back, rump, belly, and axilla (Schreiber 1976a). Complete Juvenal plumage acquired at about 70 d (P. o. carolinensis: mean 70 d [range 57–82, n = 8; Ploger 1992]; P. o. californicus: mean 69.5 d [range 63.5–83.5, n = 50; Pinson and Drummond 1993]). Belly white, rest of feather coat brown.

Ectothermic at hatching, gradually becoming endothermic as body mass increases and down coat and ability to gular-flutter develop (Bartholomew and Dawson 1954). Before endothermy achieved about 3 wk after hatching, nestling temperature regulated by constant parental brooding (Bartholomew and Dawson 1954, Schreiber 1976a). Nestling Peruvian Pelican becomes endothermic when body mass >200 g (Duffy and Ricklefs 1981).

Siblings frequently fight to establish dominance hierarchy. Fighting begins in first week after hatching, occurs independently of feeding. Larger, first-hatched nestling generally establishes dominance over siblings by pecking and biting them, with most blows directed toward head and neck (Ploger 1992, Pinson and Drummond 1993). Younger siblings often peck back, but dominance reversals uncommon. Fights sometimes end with subordinate sibling assuming submissive posture, usually laying flat in nest with head and bill turned away from attacker (see Ploger 1992 for detailed descriptions). Fights often lead to siblicide, with subordinate sibling(s) beaten to death or dying from starvation after being driven from nest and/or prevented from feeding (Ploger 1992, Pinson and Drummond 1993).

Nestling able to push itself backward at 2–4 d, hold head upright and move in coordinated manner by 8–10 d. Mostly lies prone in tree nest until 24–25 d, then sits or stands upright (Schreiber 1976a). In ground-nesting colonies, however, nestlings become mobile, leave their nests, and forms crèches 3–5 wk after hatching (Blus and Keahey 1978, Pinson and Drummond 1993, Shields 1998). First flight occurs at mean age of 61 d in P. o. carolinensis in Panama (Montgomery and Martínez 1984). In Florida, short (3–10 m) flights made at about 70 d if disturbed (Ploger 1992), but first sustained flight not made until average of 76 d (range 71–88, n = 36; Schreiber 1976a) to 81.3 d ± 2.1 SD (n = 7; Ploger 1992). First flight in P. o. californicus occurs at 78.1 d (range 70.5–85.5, n = 50; Pinson and Drummond 1993). Able to swim prior to attaining flight (MAS).

Brooding

Nestlings brooded continuously for 3 wk after hatching, with parents alternating shifts. At least 1 parent remains at nest at all times to guard nestlings until they are 4–6 wk old. Parents then spend decreasing amounts of time at nest, arriving only to feed, then leaving to forage or loaf. Parents do not spend night on nest after nestlings 5–6 wk old (Schreiber 1977a).

Feeding

Begins within a few hours of hatching and continues until young in tree nests begin flying at 11–12 wk (Schreiber 1977a); young in ground colonies fed for unknown period after attaining flight (Chapman 1908). Both parents feed, on alternate shifts. Gradual transition from indirect to direct feeding occurs during first 4 wk after hatching (Pinson and Drummond 1993). Parent initially regurgitates mass of well-digested fish or several small fishes onto nest floor, which nestlings clumsily peck and swallow. As size and coordination increase, nestlings begin to intercept regurgitated food from parent’s pouch. Beyond 3–4 wk of age, nestlings feed almost exclusively by reaching down parent’s throat to obtain whole fish (Schreiber 1977a, Pinson and Drummond 1993). After withdrawing head from parent’s throat, nestling often exhibits convulsive behavior: partially spreads wings and lays head down, then raises head over back and swings it from side to side, often biting wings; function unknown (Chapman 1908).

Of 267 boluses, each containing a single prey species, regurgitated by nestlings in N. Carolina colony, 86.1% contained Atlantic menhaden (Brevoortia tyrannus), 7.1% Atlantic silversides (Menidia menidia), 6.4% Atlantic croaker (Micropogonias undulatus), and 0.4% striped mullet (Mugil cephalus; J. Brunjes IV pers. comm.). Subsample of menhaden had mean total length of 134 mm (n = 11).

In Florida, 304 boluses regurgitated by nestlings from colonies on the Atlantic and Gulf coasts contained 31 species of fishes representing 18 families (Fogarty et al. 1981). Seven species made up 77.4% of prey by frequency of occurrence: menhaden 21.1%, Atlantic threadfin (Polydactylus octonemus) 12.8%, mullet (Mugil sp.) 11.7%, pinfish (Lagodon rhomboides) 9.7%, sea trout (Cynoscion sp.) 9.7%, spot (Leiostomus xanthurus) 6.3%, and bay anchovy (Anchoa mitchilli) 6.1%. These same 7 species made up 84.6% of the mass of a sub-sample of 113 boluses, with Atlantic threadfin contributing 27.7%, mullet 17.0%, menhaden 13.6%, spot 11.1%, pinfish 8.4%, sea trout 5.6%, and bay anchovy 1.2% (Fogarty et al. 1981). A nestling at Lake Okee-chobee regurgitated several 5– to 10-cm sunfishes (Lepomis sp.; Smith and Goguen 1993).

Regurgitations from nestlings in Puerto Rico and the U.S. Virgin Is. consisted mainly of dwarf herring, sardines (Harengula spp.), and anchovies (Anchoa lyolepis), with smaller amounts of 5 other species; mean total length 59 mm ± 3 SE (n not specified). Older nestlings and fledglings fed same-size fish as younger nestlings (Collazo 1985).

In S. California Bight, 167 nestling-regurgitation samples collected between 1972 and 1979 contained the remains of 2,195 fish, 92.4% of which were northern anchovy, 3.1% Pacific saury (Cololabias saira), 2.0% rockfish (Sebastes spp.), 1.6% Pacific mackerel (Scomber japonicus), 0.6% topsmelt (Atherinops affinis), 0.2% white croaker (Genyonemus lineatus), 0.05% blacksmith (Chromis punctipinnis), and 0.05% surf perches (Embiotocidae; U.S. Fish Wildl. Serv. 1983). Anchovies regurgitated by prefledglings on Santa Barbara I. in 1980 averaged 110.5 mm standard length (range 85–135, n = 113), those from Anacapa I. in 1979 and 1980 averaged 103 mm standard length (range 85–135, n = 172; Sunada et al. 1981). Pacific sardines and northern anchovies equally abundant in nestling regurgitation samples since 1993 (F. Gress pers. comm.).

On Isla Isabel, Mexico, 23 fish regurgitated by 2 adults feeding 4-wk-old nestlings were 97–257 mm total length (mean 160 mm), and 12 fish regurgitated by 10-wk-old young measured 64–172 mm total length (mean 101 mm; Pinson and Drummond 1993). Families represented in these samples included Gerreidae, Engraulidae, Clupeidae, Polynemidae, and Mugilidae.

Rate of feeding highly variable among and within broods. In N. Carolina, 17 broods observed for 1–3 h/d during first 3 wk after hatching received 0–1.1 feeds/h (mean 0.6 ± 0.3 SD [n = 169 nest-hours]; Shields 1998). Five of 20 broods under continuous daylight observation in Florida received no food on 3 of 6 days (Ploger 1997). Rate of feeding, but not amount of food, decreases with increasing age of brood. During daily morning (07:00–10:00) and afternoon (15:00–18:00) observation periods, nestlings in Mexican colony received an average of 4 feeds/h when 1–5 d old, 2.8 feeds/h when 11–15 d, and 1 feed/h when 21–25 d (Pinson and Drummond 1993). Because parent may regurgitate several meals following a single feeding trip, number of feeds not equivalent to number of feeding trips. Within broods, amount of food received varies with order of hatching. In 2-chick broods in Mexico, first-hatched nestling fed significantly more often and received significantly more food than second-hatched (Pinson and Drummond 1993). In 3-chick broods in Florida, first- and second-hatched nestlings fed similar amounts, but both fed significantly more than third-hatched (Ploger 1997). Nestlings able to withstand starvation for minimum of 2–3 wk, then grow normally once feeding resumed; long-term health and survival effects unknown (Schreiber 1976a).

Nest Sanitation

In N. Carolina colonies, parents and nestlings still confined to nest generally defecate on or beyond rim of nest, not in nest bowl (MAS). However, on desert islands in Gulf of California, parents commonly defecate in nest and on nestlings ≤3 wk old, apparently to help cool them (D. Anderson pers. comm.). Nestlings in Florida commonly covered with guano by 5–6 d of age (Schreiber 1976a). Fecal sacs not produced. Nest site frequently littered with eggshell fragments and pieces of dried fish, sometimes body of dead nestling trampled into nest floor. In Gulf of California, parents threw from nest eggs that had collapsed during incubation, along with nest material soiled by egg contents (Keith 1978). Parents in N. Carolina observed jabbing bill repeatedly into bottom of nest and flipping out material (MAS); function unknown, but may be related to sanitation. Fowl ticks (Ornithodoros spp.) often inhabit ground nests (see Demography and populations: disease and body parasites, below).

Carrying Of Young

Not known to occur.

Not known to occur.

Not known to occur.

In Florida mangrove colonies, young depart nest with first flight at 11–12 wk and do not return; rarely fed by parents away from nest (Schreiber 1976a). On Taboga I., Panama, young first fly at average age of 61 d, but leave nest for last time at mean of 96 d. No parental feeding detected during this 35-d period, but observations infrequent (Montgomery and Martínez 1984). In ground-nesting colonies, young remain in crèches and continue to be fed by their parents for an unknown length of time after attaining flight (Chapman 1908, Forbes 1914).

May wander extensively, especially in first year (Mason 1945, Schreiber 1976b), but often returns to vicinity of natal colony in subsequent breeding seasons (King et al. 1985, Schreiber and Mock 1988). Rarely breeds in established colony while in immature plumage (Blus and Keahey 1978), but may found new colony (Williams and Joanen 1974, Schreiber and Schreiber 1982). Not as successful at plunge-diving as adult (see Food habits: feeding, above).