Breeding

Colony Occupation

In ne. U.S., arrives at colonies a full month before copulation and egg-laying to establish territories and nest sites, in early to mid-Apr (Bongiorno 1970, Montevecchi 1978). In Caribbean, arrives at colonies much closer to egg-laying (JB).

Pair Formation

Occurs just before arrival at colony, in stop-over areas such as Delaware Bay, or on breeding grounds (Moynihan 1958b, Burger 1976). Some courtship occurs on beaches along coasts, on sandy islands, or on salt-marsh wrack before territory acquisition. Once birds arrive on colony, territories are quickly acquired, and courtship and pair-bond maintenance occur on territory (JB). In pre-egg period, courtship levels high in early morning and late afternoon (Burger 1976). At midday, birds may be away from colony foraging, or remain in colony resting.

Nest-Building

Occurs just before egg-laying, particularly in salt-marsh colonies (Bongiorno 1970, Burger 1976, 1977a). Nest nearly completed in salt marshes before egg-laying (Montevecchi 1978). In dry land colonies in Florida and Texas, some nest-building occurs just before egg-laying, but remainder is completed afterward. Continues nest-building throughout incubation, particularly during rising tides (Burger 1978) or high winds (Puerto Rico, Texas; JB).

Egg-Laying

Figure 5 . On Little Tobago I., first eggs laid late Apr–early May (Morris 1984); in Virgin Is., early May (Norton 1986); in Texas, 21 Apr–7 May (White et al. 1983a, Mueller and Glass 1988); in Florida, 1–15 Apr (Dinsmore and Schreiber 1974, Schreiber et al. 1979); in New Jersey, 9–18 May (Bongiorno 1970, Burger and Shisler 1978, Montevecchi et al. 1979); in Massachusetts, 21 May (Nisbet 1976). Timing of nesting in extreme s. Florida varies considerably among years and colony sites (mid-Apr to Aug), perhaps due to recent and marginal status of species as a breeder there (Frohring and Kushlan 1986).

Peak Laying

On Little Tobago I., mid-May (Morris 1984); in Florida, 26 Apr–5 May (Schreiber et al. 1979); in New Jersey in mid-1970s, 12–21 May (Burger and Shisler 1978), but 27 May in mid-1960s (Bongiorno 1970). Peak of egg-laying stable in Brigantine, NJ: 22–27 May in 1966–1974 (Montevecchi et al. 1979). In all regions (except s. Florida), peak of egg-laying occurs over 2-wk period.

Hatching

Peaks end of May to early Jun in Texas (White et al. 1983a); 12–28 Jun in New Jersey (Bongiorno 1970, Montevecchi et al. 1979). Hatching intervals for clutch: 1–2 d in Florida (Schreiber et al. 1979), 1–3 d in New Jersey (JB).

Fledging

Able to fly at 35–50 d (mean 42.5) in Florida (Schreiber and Schreiber 1980), at 35–42 d in Texas (White et al. 1983a). After fledging, may remain on colony 3–5 wk in Texas (White et al. 1983a), 1–5 wk in New Jersey (JB).

Second Broods

No second broods, but pairs may re-lay if eggs or young chicks lost to predators or floods.

Postbreeding

Parents and young may remain near colony up to 5 wk (Burger 1980), then disperse along coasts until directed migration begins (based on wing-tag reports; JB).

Colony-Site Selection

Nests in colonies of a few pairs up to 25,000 (Schreiber et al. 1979, Burger and Shisler 1980). Colony-site selection depends on available habitats: in ne. U.S., selects rocky or vegetated islands; in mid-Atlantic, salt-marsh islands high enough to prevent tidal flooding; in Florida and along Gulf Coast, dry islands; in Caribbean, coral or vegetated islands (Bongiorno 1970, Nisbet 1971, Montevecchi 1978, Burger 1979b, Burger and Shisler 1980, Patton and Hanners 1984, Burger and Gochfeld 1985, Frohring and Kushlan 1986).

Turnover rates used as indication of colony stability. Turnover rates are 10% in N. Carolina (McCrimmon and Parnell 1983); 19% on Delmarva Penninsula (between Chesapeake and Delaware bays) and 20% in New Jersey (Erwin et al. 1981); and 29% in Florida keys (Frohring and Kushlan 1986). Of 26 known colony sites in Florida keys, fewer than half used each year from 1976 to 1982 (Frohring and Kushlan 1986).

Colony-site selection in ne. U.S. is a compromise between nesting on low islands to avoid mammalian predators and Herring Gulls, and nesting on islands high enough to avoid tidal flooding. There are no mammalian predators on low islands because they are killed during high winter tides and can only reach distant islands when there is ice cover. Laughing Gulls will shift colony sites to higher salt-marsh islands following excessively high tides that result in low reproduction, despite presence of Herring Gulls (Burger 1979b, Burger and Shisler 1980).

Most colonies monospecific, but other species nest among or near Laughing Gulls, including Common Tern (Sterna hirundo), Forster’s Tern (S. forsteri), Least Tern (S. antillarum), Herring Gull, Great Black-backed Gull, Black Skimmer (Rynchops niger), American Oystercatcher, Willet, and Clapper Rail in continental U.S. (Dinsmore and Schreiber 1974, Burger and Shisler 1978, JB); and Royal, Sandwich (S. sandvicensis), and Bridled (S. anaethetus) terns, Brown Noddy, and Brown Booby (Sula leucogaster) in the Caribbean (Burger and Gochfeld 1985).

Colony-site selection in Puerto Rico depends on presence of densely nesting terns and boobies; Laughing Gulls cannot nest among terns because of their density, or near boobies because of their size.

Nest-Site Selection

Variable substrates from sand and rocks to salt marshes and heavily vegetated dry land. Nest-site selection studied extensively on salt marshes (Montevecchi 1978, Burger 1977a, 1979a, Burger and Shisler 1980) where species prefers either mats of dead vegetation (eelgrass [Zostera spp.] or cord-grass stems) near water or higher grassy areas of marsh (Montevecchi 1978). Mats stabilize nest during flooding. In some salt marshes, Laughing Gulls select places with less dead grass cover and more live green grass, usually Spartina alterniflora (Burger and Shisler 1978). Laughing Gulls select higher places when available; flood losses inversely related to elevation and vegetation. Percent nests flooded out: in S. alterniflora 100%; S. patens 52%, Juncus 28%, and bushes 4% (Burger and Shisler 1980).

Vegetation is important determinant of nest placement: nearest neighbors nest in direction of least visibility as measured with fisheye lens; removal of vegetation more than doubles aggression rates between neighbors (Burger 1977a).

In Puerto Rico, vegetation also affects nest-site selection: Laughing Gulls select sites near dense vegetation, of intermediate height, providing good visibility from nests and protection and cover from predators and the sun (Burger and Gochfeld 1985). Requires open spots since dense and tall vegetation prevents view of predators and hinders escape from nests. Individuals nesting in Culebra, Puerto Rico, nested in taller (average height 32, 52, and 60 cm in 3 colonies), denser vegetation than birds nesting farther north along the Atlantic Coast (average height 22, 28, 35, and 42 cm in 4 colonies), which partially reflects temperature differences (Burger and Gochfeld 1985).

In mixed-species colonies with large gulls, Laughing Gull usually forced to nest in more open areas that are lower in elevation (New Jersey); in mixed-species colonies with herons and egrets, Laughing Gulls forced to nest in less-vegetated areas (Texas); and in mixed-species colonies with large terns, forced to nest in vegetation, as terns use the bare places (Puerto Rico; JB).

Construction Process

Usually both sexes build nest, but if male fails to find a mate, he may begin building a nest or nest platform, which is then used for soliciting mate (JB). Male may bring more of the nest material; female may arrange material by settling movements (Noble and Wurm 1943, Burger 1977a). Nest-building involves many components, including Sideways-building, consisting of reaching over the nest, picking up material, and placing it on the rim of the nest (Moore 1975). On dry land habitats, eggs may be laid before nest is complete; in marsh colonies, nest is mostly complete before egg-laying (Burger 1978, 1979b, Schreiber et al. 1979). After egg-laying, nest is complete on dry land colonies, and no more nest material is added (Schreiber et al. 1979); in marsh colonies, material is added throughout incubation and early brooding phase (JB).

Nest location influenced by tidal reach, presence of vegetation, and presence of debris such as eelgrass wrack (Bongiorno 1970, Nisbet 1971, Burger 1978). Experimentally cutting grass in salt marshes prevents nesting; creating piles of debris increases nesting (Bongiorno 1970). Nest-building affected by condition of nest and flooding: Sideways-building increases when the nest rim is partly destroyed, even during mid-incubation (Moore 1975).

Structure And Composition Matter

Salt marsh vegetation or whatever grasses are available (Burger 1977b, Fig. 6).

Dimensions

Nests in Barnegat Bay, NJ, salt marshes: cup width 139.2 mm (SE 3.1), cup depth 60 mm (SE 2.4), nest width 280 mm (SE 5.8), height of rim above marsh mud 280 mm (SE 14 mm) (n = 150; JB).

Microclimate

No data.

Maintenance Of Nests

From Burger 1978, 1979a . Nest maintenance important in salt-marsh colonies where nest keeps eggs and chicks above flood tides; strong nests that are attached to vegetation do not float away during storm tides (JB). In intermediate tides, nests float but remain in place, and eggs stay dry. Nests also serve as platforms for activities of parents and young, preventing vegetation from intruding. In marshes, both members of pair continue to add nest material throughout incubation and early chick care. Nest width in salt marshes increases from a mean of 280 to 320 mm from laying of first to third egg, continues increasing to mean of 350 mm when chicks are 5 d old, then decreases to about 280 mm by fledging.

Parents respond to environmental conditions and add material accordingly. Following heavy rain and natural flood tides, nest material added to smaller nests to make them higher and wider. Experimental manipulation to wet entire nest, wet only cup, remove half of nest, and remove only cup all resulted in significant additions of nest material up until chicks were 5 d old. Laughing Gulls built nests higher than prior to treatment, except for removal of half of nest, where they built the side up to equal the undisturbed side. Laughing Gulls added more material to nests than did other marsh-nesting species, including Common Tern, Herring Gull, and Clapper Rail.

Shape

Ovate to elliptical ovate or pyriform.

Size

Mean varies among years and locations. Mean length (mm) of eggs is 52.0 (SD = 2.1) for Trinidad (1976, Morris 1984); and ranges from 47.0–58.9 for Florida (1972–1976, Schreiber et al. 1979); and 47.5–58.8 (1972–1974) and 45.3–59.8 (1995) for New Jersey (JB). Egg width (mm) mean of 37.1 (SD = 0.9) for Trinidad (1976, Morris 1984); and ranges from 43.8–40.6 for Florida (1972–1976), Schreiber et al. 1979); ranges from 32.2–38.1 (1972–1974) and 31.9–39.4 (1955) for New Jersey (JB).

Mass

Mean weight (g) of eggs in Florida: A egg (first egg laid) = 41.5–43.4 (SD 2.7); B egg (second egg laid) = 38.7–43.2 depending on site (ranges from 2.9–3.4); C egg (third egg laid) = 36.3–39.2 (SD 3.0) (n = 60; Schreiber et al. 1979). Yolk comprises 33.2% of wet weight of egg, albumen 57.7% (Ricklefs et al. 1978). Whole egg contains 63.7% water, 46.4% lipid (Ricklefs 1977), energy content = 1.44 kcal/g fresh weight with shell (Schreiber and Lawrence 1976). Size of yolk directly related to size of egg (Ricklefs et al. 1978).

Color

Ground color varies from cream (rare) and brownish buff to dark brown, greenish buff, and olive brown. Brownish or blackish splotches vary in size and shape. Eggs occasionally lack splotches or have them concentrated in ring at large end (JB). Base color of 417 eggs in Barnegat Bay, NJ (1994, 1995): 23% light brown, 20% tan, 20% olive tan, 12% brown, 10% olive green, 7% olive brown, 6% light tan, 1% olive blue, and <1% blue or green without splotches.

Surface Texture

Smooth.

Eggshell Thickness

Eggshell thinning detected at all colonies examined in Texas, ranging from 7 to 14% (White et al. 1983a).

Clutch Size

Usually 3, except in tropics. See Demography and Populations: measures of breeding activity, below.

Egg-Laying

In Florida, mean interval between first and second egg: 2.03 d (SD 0.4) for 3-egg clutches, 2.73 d (SD 0.8) for 2-egg clutches; between second and third egg, 2.30 d (SD 0.4) (Schreiber et al. 1979). In Barnegat Bay, NJ, 78% of intervals between eggs were between 24 and 48 h (JB). In Florida, 64% of 42 eggs laid between 1900 and 0700 h (Schreiber et al. 1979).

Renesting rare unless eggs lost during tidal flooding early in incubation, and when all colony members are renesting.

Onset Of Broodiness And Incubation In Relation To Laying

Both sexes begin incubation with laying of second egg, rarely not until laying of third (JB).

Incubation Patch

Three present in both sexes, 2 in front, 1 behind.

Incubation Period

In Florida, 22–25 d (Schreiber et al. 1979); in Barnegat Bay, NJ, 23–27 d (Burger 1980, JB).

Parental Behavior

Normally cover eggs 98% of time during incubation, both day and night (Burger 1976). Both parents incubate; duration of shifts similar for males and females. Normal bouts 20 min–3 h (Burger 1980).

Adults able to distinguish own egg from artificial eggs that resemble them closely in form and color (Noble and Lehrman 1940). Brooding Laughing Gulls are attracted to the eggs, nest site, and nest. They will retrieve eggs, particularly when all eggs are displaced from nest and they are close to the nest (Noble and Lehrman 1940). Eggs of abnormal size will be incubated, but not eggs that have a hole punctured in them (Noble and Lehrman 1940), as might occur with predation.

Hardiness Of Eggs Against Temperature Stress And Flooding

Few data available, but eggs able to withstand some tidal inundation for <6 h without killing embryos (JB).

Preliminary Events And Vocalizations

Calls emanating from pipping eggs responsible for behavioral changes in adults. Incubating birds respond to calls from hatching chicks played experimentally from beneath their eggs by increases in frequency of looking down, rising-resettling, shifting the eggs, quivering while sitting, and calling, and by decreases in nest-building (Impekoven 1973). Adults become more responsive to chick vocalizations as functional incubation proceeds (Impekoven 1973).

Shell-Breaking And Emergence

Young enlarge initial pipping hole with egg tooth, resting between bouts of chipping at shell. Interval between initial star and hatching usually 28–46 h. Interval between hatching of first and second egg usually 3–6 h; between second and third egg, 1–5 d (JB).

Parental Assistance And Disposal Of Eggshells

Generally removes eggshells following hatching; eggshells not removed can lodge over slightly smaller unhatched third eggs, preventing hatching (JB). Sixty-three percent of large shell fragments found near nests (mean = 80 cm), mean distance from rim correlated with size of nest platform; also removes foreign objects placed experimentally in the nest (Snodderly 1978).

Asynchrony

First 2 chicks usually hatch only 3–6 h apart, last chick 1–5 d later. Staggered hatching of brood associated with reduced survival in later-hatching chicks, which are at disadvantage when competing for food from parents, based on age and size (Hahn 1981). An experimental study of broods arranged to hatch synchronously showed that parents with 3-egg clutches that hatch asynchronously have higher reproductive success (Hahn 1981).

Condition At Hatching

Shortly before hatching begins, adults increase Crooning (see Sounds: vocalizations, above), which stimulates newly hatched chicks to peck at parent’s bill. Chicks semiprecocial; eyes closed until dry, down-covered, stay in nest after hatching without standing for up to 2 h. Mass at hatching: 25–35 g (Florida, n = 65; Schreiber and Schreiber 1980); mean 30.1 g (SD 0.2, Barnegat Bay, NJ, n = 35; JB).

Chick size related to egg size; water level increases and lipid level remains constant in newly hatched chicks with increasing egg (and chick) size; weight of newly hatched chick averages 64.1% of weight of fresh egg (Ricklefs et al. 1978).

Newly hatched chicks do not usually move or stand until down is dry and eyes are open. Within first 3 h, down usually dries; within first day, body movements are coordinated and chicks utter soft cheep calls. Chicks respond to parent calls but do not recognize own parent for several days.

Growth And Development

In Florida, mass increases rapidly from hatching (when chick weighs about 10% of adult mass) until 30 d when asymptotic weight reached (mean 300 g; Schreiber and Schreiber 1980). Culmen 13–16 mm at hatching, 35% of adult length; increases in a straight line until 12 d, when growth slows. Culmen 88% of adult size at fledging (Schreiber and Schreiber 1980).

Tarsus 23–28 mm at hatching, 45% of adult size; reaches asymptote at 36 d, adult size at fledging. Rectrices first appear at 13 d, grow slowly at first and rapidly from 20 to 42 d, when 88% adult length. Mean wing length at hatching 19.3 mm; increases slowly until 14 d, rapidly thereafter, reaching 81% of adult size at fledging and adult size at 55–60 d of age (Schreiber and Schreiber 1980).

In Florida, fledging success did not differ as a function of hatching weights (Schreiber et al. 1979). Laughing Gull chicks can first fly at 32 d of age (Burger 1980), although full flight usually at 35–40 d in New York (JB), 35–50 d in Florida (mean 42.5; Schreiber and Schreiber 1980).

Molt into Juvenal Plumage. Published information only from Florida (Schreiber and Schreiber 1980). Scapular feathers first of Juvenal plumage to appear; sheaths emerge at 5–8 d of age, unfurled feathers 6–20 mm long at day 10, up to 50 mm by 20 d, and 90 mm (full length) at 30 d. Feather sheaths gone by 22–25 d. Primary growth parallels that of scapulars; maximum sheath length of 45–47 mm reached at 26–43 d, sheaths gone by 42–48 d.

Rectrices appear at 13–25 d, continue growing until fledging, when 70–120 mm. Maximum sheath length 28–30 mm at 28–44 d (Schreiber and Schreiber 1980). Coverts first appear at 8–11 d, secondaries at 9–11 d. Down remains on primary, secondary, and rectrix feather tips until 20 d, only on belly, rump, inner legs, neck, and head at 30 d, only on flanks of some birds by 40 d; no down at fledging.

Primary, secondary, and rectrix growth highly variable; related to food available; chicks below mean weight for their age show slow feather growth (Schreiber and Schreiber 1980).

Control of Body Temperature. Recently hatched chicks <32 h old have moderately effective temperature control; decline in cloacal temperature more conspicuous at temperatures below 20oC; chicks effective at thermoregulation at high ambient temperatures (Dawson et al. 1972). No published information for adults.

Behavior. Newly hatched chicks remain quietly on nest until dry, then begin to stand and move about the nest (JB). From days 1 to 5, chicks normally remain on nest platform, or move off nest to adjacent vegetation to avoid thermal stress or when parents give Alarm Calls (see Sounds: vocalizations, above); young chicks do not normally wander off the nest or move >10 cm from nest platform (JB). Immediate response to arrival of parent is to orient toward parent, call, and approach. After 5–7 d, chicks may wander farther from nest, particularly during Alarm Calling by parents and other colony members. Wandering too far from nest can result in getting lost or straying into neighboring territories where adults may attack and kill chicks (Burger 1979b).

Wild-reared chicks peck preferentially at models of Laughing Gulls over models of Herring Gulls; newly hatched chicks in laboratory have no preference (Hailman 1967). Based on laboratory studies, species preference for pecking develops on basis of reinforcement and conditioned habituation (Margolis et al. 1987). Chicks peck less often at parent’s bill when hearing alarm call kow than other calls (Impekoven 1970).

When tested experimentally away from colony, Laughing Gull chicks 6–13 d old, raised by their parents, respond to calls of own parents with orientation toward sound, approach, increased locomotion, and vocalization; in response to calls from nonparent adults, chicks orient away from speaker, withdraw, and sit or crouch (Beer 1969, 1970a). The tapes contained ke-hah, Mew Call or Crooning, and Long Calls. When 6- to 8-d-old hand-reared chicks from the same broods as parent-raised chicks were tested with playback calls of parents and nonparents, parent-raised chicks oriented and moved toward parent calls in preference to nonparent calls, whereas hand-reared chicks crouched in silence at both types of calls (Beer 1970a). When parent-reared chicks were tested with a similar protocol, 1- to 3-d-old chicks showed the least evidence of parental recognition, 6- to 8-d-old chicks showed the greatest response, and 12- to 28-d-old chicks showed intermediate levels of response (Beer 1970b). Approach to parent’s calls was stimulated by Mew Call and suppressed by Ke-hah and Long calls in young chicks, but older chicks required all 3 calls (Beer 1970b). Beer’s experiments also indicate the importance of using playbacks of parental calls from the proper age; the quality of parental calls changes with season and hormonal state (C. G. Beer pers. comm.).

Parents learn to recognize calls of their chicks more from response of the chick than from the call itself; in nature, parents orient toward and approach both the playback of calls of their own and foreign chicks (Beer 1979). However, when chicks are placed in covered boxes near their nests, parents respond differentially to the box with their own chick, suggesting that they are responding to the more frequent calls of their own chicks (Beer 1979).

Details on chick displays in Moynihan 1959 . Postures include squat or crouch when very young, sit and stand after 1 d, Upright posture when 8–10 d old; give soft begging calls within 2 d of hatching. Very young chicks try to bury themselves under intruding conspecific, or crouch in nest silently. Escape behaviors to avoid predators or other disturbances include crouching on nest, retreating to edge of nest, burrowing in nest material at edge of nest, retreating to edge of nest to hide in vegetation, or moving a few centimeters from the nest to hide in vegetation (JB). Bill-down Crouch is ritualized by 1 wk; chick squats with bill and head tucked under body, facing away from attack or intruder; chick will remain squatting while intruder steals nest material from beneath it. Older chicks either hide in vegetation or assume a Hunched Posture (see Behavior: agonistic behavior, above) when conspecific intruders land; some chicks begin overt attacks by age 14–18 d. Chicks do not normally attack siblings; sibling recognition seems to develop with parental recognition (JB).

Attack behavior includes unritualized attack by 14 d; by 14–16 d, chicks tentatively attack intruding chicks or neighbors that walk onto nest; usually give kakakakaka calls (Gakkering: see Sounds: vocalizations, above) to intruders. By 21 d, chicks vigorously defend their nest and territory from intruders, charging toward intruders that come within 1–2 m of the nest.

Where thermal stress not a problem, undisturbed chicks usually remain on the nest, or in the vicinity of the nest until fledging; in southern parts of range, move to vegetation to seek shade. Small chicks are difficult to find in dense vegetation, but as they grow larger, banded chicks can be located only a few centimeters from the nest. Chicks may seek the cover of nearby vegetation to avoid thermal stress or heavy rains, but return to nest when parents land with food. When disturbed repeatedly, chicks may wander several meters from nest, but return when disturbance passes. Chicks normally return to nest before parents, but with prolonged disturbance, chicks may be called back to nest by Long or Mew calls of parents. Chicks are fed by their parents on the nest; at 35–40 d, chicks make short flights around the colony, or out to land on and bathe in the water, but usually return immediately to the nest and territory.

Brooding

At hatching, chicks brooded 90–95% of time; both parents brood; brooding declines gradually until chicks are 8–10 d old, then ceases. In first week, females brood more than males; thereafter parental care is equal. Parents accept any chick until 3–5 d old, then reject, but this rejection most likely based on behavior of chick rather than recognition (Beer 1979). After 6–8 d of age, chick recognizes parent and responds accordingly.

Feeding

Both parents feed chick from hatching to at least 2–3 wk after flying; most feed until chick is 60 d old (Burger 1980). Food brought back to nest at all times of day, most frequently at dawn and dusk. With very young chicks, parents regurgitate food into chick’s bill; at 3–7 d, parents regurgitate food onto nest and chicks feed from there; with older chicks, parents begin to regurgitate and chicks grab food from bill before it hits ground (JB).

Food Of Young

Depends on location; Bent (1921) reported chicks eat mainly fish and small fry. In Barnegat Bay, NJ, in 1970s–1990s, mostly insects and fish with some horseshoe-crab eggs (JB); near Delaware Bay, 60% of chick diet is horseshoe-crab eggs in 1990s (Burger and Wagner 1995). Since 1920s, some Laughing Gulls have switched to feeding on garbage, particularly during the nonbreeding season; but most parents feed chicks natural foods (L. Wagner unpubl. data, JB).

Nest Sanitation

Incubating birds fly 10–40 m from nest to defecate; chicks back to edge of nest to squirt outside nest. Parents remove eggshells and other foreign objects and drop them away from nest.

No evidence that it occurs.

No evidence that intraspecific brood parasitism occurs regularly; occasionally a fourth egg laid in a nest is from a different female, on the basis of color pattern and timing of appearance (many days after clutch completion; JB).

At fledging, family groups remain together for at least 10–14 d after they leave colony, based on wing-tagging data (Burger 1980). Colony is usually abandoned 2–3 wk after young can fly, although a few young may linger. Fledglings leave colony with adults and remain within general area of colony for additional 2–3 wk. Percentage of chicks returning to nest site to be fed begins decreasing at about 34 d of age, reaches zero at about 60 d of age (25 d postflight; Burger 1980); some chicks fed away from colony at older ages (JB).

Details unknown from period of postbreeding dispersal. Mixed flocks of juveniles and adults feed along coast or adjacent to coast in wet and grassy fields, ponds, lakes; also at airports and landfills.