Breeding

See Figure 6 . Most complete information from Isla Isabel, w. Mexico (Osorno 1996), quoted here.

Pair Formation

Covers ≥6 mo in population (Oct or Nov to early Apr) but lasts few days in individual.

Nest-Building

Peaks few days after pair formation; lasts about 13 d.

Broods Per Season

Invariably 1 or less, due to protracted breeding cycle (see Behavior: sexual behavior, above, and Young birds, below).

Egg-Laying Period

Extends over about 6 mo, with most eggs laid over 2 mo (Kepler 1978). At some sites laying is multimodal, arising from highly synchronous and spatially-aggregated pattern of communal male display, leading to within-group synchrony in laying and subsequent waves of new or repeat laying as nest losses make space available for displaying males among groups of nests (Carmona et al. 1995, Osorno 1996); most estimates inferred from laying dates back-calculated from chick bill-lengths, and remain to be confirmed by intensive monitoring of marked adults and nests. New breeding period begins while flying juveniles from previous breeding are still being fed by females.

Laying Periods. At Barbuda (17°35´N) mid-Sep to late Jan 1970–1971, with 2 peaks Oct–Nov and Dec–Jan (Diamond 1973); early Oct to mid-Jan with peak second half of Nov 1988–1989 (W. Trivelpiece pers. comm.); at Monito I., Puerto Rico (18°10´N), between Oct and Apr, most late Oct to mid-Dec (Kepler 1978); Great Tobago, British Virgin Is. (18°N) Aug–Oct (EAS); at Man-o’-War Cay, Belize (16°53´N) between mid-Dec and Apr, median late Feb–early Mar, i.e. about 2.5 mo later than Barbuda and Monito I. (Trivelpiece and Ferraris 1987); and at Isla Santa Margarita, Mexico (24°25´N) 4 hatching peaks 5–6 wk apart between late Dec and early May (Carmona et al. 1995); at Isla Isabel, w. Mexico (21°52´N, 105°54´W) laying peaked early Nov 1993 and 1994 (Osorno 1996). Repeatability of laying season indicated best for Monito I., where apparently remained consistent over 30 yr (Kepler 1978); Barbuda colony showed similar phenology in early 1970s and late 1980s; Belize colony studied for <1 mo in 1980; and though Mexican site (Isla Santa Margarita) studied over 3 yr, laying dates reported for only 1 yr (1988). Most records listed by Eisenmann (1962) are consistent with laying season concentrated in winter. Peak of laying and hatching within Trade Wind season may be related to phenology of food availability (which is unknown), but also to energetics of this most-aerial of birds whose flight performance is likely enhanced by moderate winds (Harrington et al. 1972), and which requires a steady wind to land accurately at the nest site (Diamond 1973, Kepler 1978).

Selection Process

Two stages; first male selects display site, then female selects mate; nest invariably built on display site (Osorno 1996).

Microhabitat

Upper surface of canopy of low trees or shrubs.

Site Characteristics

Situated normally on flat tops of low bushes or trees, usually no more than a few meters above ground; sometimes on grass tussocks or even bare ground. Mangroves used most often, but sea-grape (Coccoloba uvifera), cactus, sea-lavender (Limonium sp.), and gumbo limbo (Bursera simaruba) also recorded (Eisenmann 1962). Suggestion by Murphy (1936) that colony sites are dictated by frigatebirds’ need to take off into the wind is not supported by observations that they can take off in calm air or even from ground or water; importance of wind direction is in landing accurately on a small and fragile nest site, not in taking off (which need not be accurate). Colonies usually situated such that a bird attempting to land on its nest can do so into the wind, “like a tanker docking against the tide” (Diamond 1973: 201); sites exposed to full force of wind, or completely sheltered from it, are avoided (Diamond 1973, Kepler 1978). Colonial, often grouped in subcolonies arising from groups of males displaying together. Often spaced close enough that “adjoining sitters can fence with their bills” (Eisenmann 1962:374) but not ‘often touching’ as described by Cramp and Simmons (1977). Measured nest densities 0.28/m²on Barbuda, e. West Indies (Diamond 1973), 1.3/m²in Bahamas (Eisenmann 1962), and 0.87/m²in Belize (Trivelpiece and Ferraris 1987).

Construction Process

Flimsily constructed of small sticks and twigs collected by males from living bushes and trees in and around colony, picked off water, or stolen from other males or nests. Male brings average of 17 ± 3.6 SE (n = 22; Osorno 1996) twigs over 13 d nest-building period, while female guards nest and arranges twigs.

Structure And Composition

Nest is a flat or slightly hollowed platform. Some nests lined with finer material such as grass or vines (EAS). Female guards nests and does most building; not known whether female chooses male or his site.

Dimensions

Diameter 25–35 cm.

Microclimate

Fully exposed to sun, so hot and dry; no measurements.

Maintenance

No maintenance behavior recorded; nests become progressively reinforced by dried guano produced by chick.

Nonbreeding Nests

None recorded; but since only 33% (of 55) pairs laid an egg on Isla Isabel, w. Mexico (Osorno 1996), remaining 67% were functionally nonbreeding nests.

Shape

Elliptical ovate.

Size And Mass

Sample of 50 eggs (origins un-stated) averaged 68 × 47 mm (65–74 × 44–50 mm), calculated mass 84 g (Schönwetter 1967 in Cramp and Simmons 1977); 5 measured in Belize slightly larger, 71 × 48 mm (Trivelpiece and Ferraris 1987). Egg sizes differ significantly between colonies in Caribbean, indicating that species may not be monotypic and needs study of morphology and genetics (see Table 2).

Color And Surface Texture

White, not glossy, smooth.

Eggshell Thickness

Thickness of 16 eggshells from Belize in 1985 averaged 0.382 mm ± 0.028 SD, not different from 27 eggshells prior to use of pesticides (mean 0.386 ± 0.022 SD; Parker et al. 1987).

Clutch Size

Always 1 egg. Single-brooded. No information on replacements, but successive waves of laying following nest losses at Isla Santa Margarita, w. Mexico, may have been caused by replacement laying (Carmona et al. 1995). Cases of 2 chicks in 1 nest probably result from 2 females laying in same nest (Diamond 1973).

Onset Of Incubation

Begins immediately after laying (Osorno 1996).

Incubation Patches

None.

Incubation Period

Incubation period (n = 7) mean 56.4 d ± 1.1 SD (range 53–61 d) on Isla Isabel, w. Mexico (Osorno 1996).

Parental Behavior

Eggs attended continuously by either parent. Incubation by both sexes equally in Belize (Trivelpiece and Ferraris 1987) and Isla Isabel, w. Mexico (Osorno 1996); small sample on Barbuda, e. West Indies, suggested females did more incubation later in day and later in season (Diamond 1973). Incubating birds of both sexes often very reluctant to leave nest when approached (Eisenmann 1962, Kepler 1978). Nest reliefs so well synchronized that egg is rarely exposed; incubation shifts averaged 4 d (range 2–7 d) on Barbuda (W. Trivelpiece pers. comm.), 3 d (range <1 to 9 d) on Isla Isabel, w. Mexico (Osorno 1996).

Hardiness Of Eggs; Effects Of Egg Neglect

No data; unattended eggs invariably destroyed by intruding males taking nest material (Osorno 1996, AWD).

No information. Eggshells not found near nests so presumably removed by parent(s).

Condition At Hatching

Altricial and nidicolous. Naked at hatch; complete coat of white down is acquired by about 60 d. No information on size or coloration at hatch; eyes closed (AWD). Newly-hatched chick is feeble and inactive, lying flat in nest; usually hidden beneath brooding adult.

Growth And Development

See Figure 7 . Point of inflection of growth curve (i.e., maximum growth rate) reached at about 47–48 d (Carmona et al. 1995); reaches close to adult mass at or well before fledging (Diamond 1973, Carmona et al. 1995). Growth slow; mean age at fledging 166 d (range 149–207) at Barbuda, e. West Indies, 150 d at Isla Santa Margarita, w. Mexico (Carmona et al. 1995). At Isla Isabel, w. Mexico (Osorno 1996), fledging averaged 176 d in males and 185 d in females, but was earlier in chicks from late nests (167 d) than in chicks from early nests (185 d). By 100 d, females separable from males by longer bill (Diamond 1973, Carmona et al. 1995) and whiter wing-bar (Diamond 1973), but latter distinction not useful for fledged young (Trivelpiece and Ferraris 1987) and may not apply at all colonies (Osorno 1996). Most contour feathers (other than mantle and scapulars) grow gradually between 75 d and fledging at about 150 d. First feathers visible are mantle and scapulars, forming dark ‘cape’ between 75 d and 100 d. Rectrices and remiges conspicuous after 100 d. Endothermy assumed to be acquired at 3–4 wk (Carmona et al. 1995, following Dunn 1975). Few data on chick behavior; downy chicks adopt sunbathing posture (see Behavior: self-maintenance, above) and may lie prostrate on nest with head dangling over edge. Remain on nest until fledging; young that fell from nest not fed by parents, and died (Carmona et al. 1995). Remain dependent on female parent for food for >9 mo after fledging (Osorno 1996). Reluctant to fly, and do so poorly, for several weeks after first flight.

Nest defended by female during building, by incubating or brooding adult thereafter.

Brooding

Both sexes brood for first 4–7 wk (Diamond 1973); chick first left unattended at 3 wk (Trivelpiece and Ferraris 1987); after 6 wk, visited only to be fed (Diamond 1973), or left unattended for 50% of daylight hours (Carmona et al. 1995).

Feeding

From Diamond 1973, Trivelpiece and Ferraris 1987, Carmona et al. 1995, Osorno 1996, except as noted. Chicks fairly helpless first few days and incapable of begging. Adults poke gently at chick’s bill and dribble small amounts of mostly digested food into bill. Chick soon gains coordination and learns to peck at adult’s bill to stimulate regurgitation. As chick grows, begging and poking at adult’s bill becomes more aggressive and begging call louder and more insistent. Older young feeds by plunging bill deep into female’s throat, not by incomplete regurgitation as stated by Cramp and Simmons (1977). Fed equally by both parents until chick about 77 d old when male deserts nest and colony and female continues feeding young for remaining time in nest and 9 mo postfledging. On Isla Isabel, w. Mexico, age of chick when male deserted highly variable (mean 77.1 d ± 5 SD, range 18–161 d, n = 33); variability due to great range in laying dates but short period of year (Mar–Apr) when males desert (Osorno 1996, 1999). Female feeds flying juvenile mainly in the afternoon. Female and flying juvenile evidently recognize each other, rather than relying on meeting at nest site, as female recorded feeding marked juvenile 80 m from nest (Diamond 1973). Adults usually move to perch near nest after feeding chick.

Rate Of Feeding

In Galápagos, chicks received 2.2 feeds/d, compared with 0.7 in Great Frigatebird (Cepeda and Cruz 1994). This observation led to inference by Diamond (1972, 1973) that Magnificent feeds closer inshore than other frigatebird species (see Food habits: feeding, above). Much less frequent feedings (0.29/d, n = 31) at Isla Isabel, w. Mexico (Osorno 1996) are anomalous in this respect.

Nest Sanitation

None: guano accumulates on and under nest during chick-rearing period.

Carrying Of Young

Not observed.

Not recorded in frigatebirds.

Not recorded in frigatebirds.

Departure From Nest

Normally at 150–185 d of age, but remains in vicinity of nest for 5–13 mo more, being fed by female parent near nest-site (Diamond 1972, 1973; Trivelpiece and Ferraris 1987, Osorno 1996). Little information on time or activity budgets during this period, but observations by Trivelpiece and Ferraris (1987) suggest that older juveniles leave the colony at dawn, presumably searching for food at sea, returning daily to the colony before dark.

Growth

No information.

Association With Parents And Other Young

Fledglings up to a year after leaving nest return to colony to be fed by female (see Behavior: sexual behavior, above); such young often aggregate in loose groups (AWD).

No information on behavior or distribution between independence and first breeding. Feeding efficiency less (by some measures) than that of adults; juveniles obtained one-quarter as much food as adults in artificial situation robbing Laughing Gulls of food provided experimentally in Mexico (Gochfeld and Burger 1981).