Demography and Populations

Age At First Breeding, Intervals Between Breeding

Age at first breeding not known; does not breed in immature plumage. By analogy with other Fregata species, probably does not breed until 5–7 yr old. Data from small sample of adults on Barbuda, e. West Indies (W. Trivelpiece pers. comm.) and Isla Isabel, w. Mexico (Osorno 1996), indicate at least some males attempt to breed every year and females every other year. While males desert colony when chicks about 3 mo old, females continue to feed fledglings until 10–16 mo old so nesting season lasts >1 yr for females. Unsuccessful females could nest annually.

Clutch

Invariably one; see Breeding: eggs, above.

Annual And Lifetime Reproductive Success

Few good data and those available reported differently making comparison among colonies impossible. Hurricanes commonly destroy breeding season in Caribbean colonies: e.g., spring 1997 hurricane destroyed nests on Great Tobago, British Virgin Is. and Barbuda, e. West Indies (EAS). Egg loss estimated at 25% of those laid, chick loss at 10% on Barbuda in 1988 (W. Trivelpiece pers. comm.); at Isla Isabel, w. Mexico, 79% of 68 eggs lost before hatching, and <51% of 78 chicks survived to fledging in 1993–1994 (Osorno 1996). Chick mortality 46% over 6 mo at Isla Santa Margarita, Mexico (Carmona et al. 1995). In good years young fledged from eggs laid may vary from 50 to 75% (Barbuda; EAS). No data on number of young fledged that survive to breed.

No data on lifetime reproductive success. Males estimated (by analogy with other frigatebird species) to live 30 yr; if breed 25 of those, could raise 12–13 young in lifetime if breed every year with 50% success. Females breed every other year for an estimated 12 yr could raise 6–7 young in a lifetime.

Number Of Broods Raised Per Season

No data. Potentially one for males, 1 every 2 yr for females owing to length of time they care for young. Only 50% of males breeding in 1 yr recorded at colony following year (Osorno 1999), so many males may take a year off between breeding efforts.

Proportion Of Total Females That Rear At Least One Brood To Independence

Unknown. Roosts of nonbreeding adult females not seen, indicating that all attempt breeding each season.

No data for this species; longevity record for Great Frigatebird 34 yr (Clapp and Hackman 1969).

No diseases reported. Adults and chicks commonly harbor flat-flies (Hippoboscidae).

Weather

All nests in colony may be destroyed and all young lost during hurricane. More common in Caribbean. El Niño events cause increased starvation of young (Valle et al. 1987); more severe in Galápagos Is. and e. Pacific than Caribbean. Eggs and chicks can be killed by exposure to hot tropical sun or to rain; generally happens only when people enter colony, disturbing adults off nests.

Predation

See Behavior: predation, above. No known natural predators on adults. If adults disturbed off nests (as by people), other frigatebirds sometimes take eggs or small young. Feral cats may take some small young (e.g., on Isla Isabel, w. Mexico; Osorno 1996).

Competition And Interference

Commonly steal nest material from each other; may cause loss of egg or small chick that gets knocked out of nest. If courting group of males forms near nesting birds (as is often the case), this increases nest disturbance and loss. Boobies nesting nearby may cause eggs or small chicks to be knocked out of nest as boobies carry on their daily activities.

Collisions And Entanglement

Mortality reported at communication towers and power lines, especially if near colony; problem greatest for fledg-lings learning to fly. Frequently found entangled in fishing lines (Parker et al. 1987); will dive on fishing lures and get caught. Young and adults sometimes die from entanglement in trees used for nesting or roosting (Trivelpiece and Ferraris 1987).

Initial Dispersal From Natal Site

Fledglings first fly from nest at about 5–6 mo of age, continue to return to nest site for >5–13 mo. Gradually spend more time away from colony. No data on where they go once no longer returning to colony to be fed. Evidently remain within few hundred kilometers of natal colony for several years at least; birds banded as chicks on Barbuda, e. West Indies, recovered within 1 yr on Antigua (1), in second year in Guadeloupe (160 km), Martinique (320 km) and Tobago (700 km; 1 each), in Haiti (1,100 km; 1 in third year), and as adults in Grenadines (550 km) and St. Martin (150 km). A chick banded off the Parana coast of Brazil in 1984 was recovered 26 mo later in Dominica, over 5,000 km to the north (Sick 1993).

Fidelity To Breeding Site And Winter Home Ranges

Unknown. ‘Winter’ (i.e., nonbreeding) range likely within few hundred kilometers of breeding colony, especially for females, since breeding season en-compasses >1 yr. Of 14 adult males tagged on Barbuda, e. West Indies, in 1988, all returned in 1989, 4 nesting close to their previous breeding site but not in same bush; of 6 females, 2 returned (W. Trivel-piece pers. comm.). Over half males breeding on Isla Isabel, w. Mexico in 1 yr, found in colony following year in breeding condition. Data on size differences among Caribbean islands (Table 1) suggest birds faithful to original breeding site. Sexes may spend nonbreeding period in separate areas (Harrington et al. 1972).

Home Range

No information.

Numbers

See Appendix . World population estimated at 59,000–71,000 breeding pairs, great majority of which are in e. Pacific and Baja California (48,000–58,000). Few colonies censused in recent years and data unreliable as to current status (Lindsey et al. 2000, Schreiber and Lee 2000). An estimated 4,300–5,300 in West Indies (Lindsey et al. 2000). Remnant population in e. Atlantic now down to 5 pairs on two small islets in Cape Verde Is. (Hazevoet 1994). Given known level of disturbance in some Caribbean colonies, others not visited recently may no longer exist (Lindsey et al. 2000); at least 10 nesting sites in Caribbean known to have been abandoned in twentieth century (Appendix). Colony on Marquesas Keys off s. Florida abandoned by 1990 owing to human disturbance (Robertson and Woolfenden 1992, Stevenson and Anderson 1994). Type specimen is from Aruba, but no colony there today. Seal Key, Bahamas, once reported to have >1,000 pairs (Bryant 1859); none there today (Buden 1987). Three large w. Mexican colonies support bulk of current population: Bahia del Pabellon (10,000–20,000 pairs), Bahia Santa Maria (18,000 pairs: Everett and Anderson 1991), and Isla Santa Margarita (20,000 pairs; Moreno and Carmona 1988).

Trends

Apparently declining in most areas for which there are data (Appendix; van Halewyn and Norton 1984, Howell and Webb 1990, Antas 1991, Lindsey et al. 2000), due mainly to human destruction of habitat for housing, resorts, etc., and disturbance in colonies. Introduced predators on islands and over-fishing are also potential problems (Schreiber 2000a, Schreiber and Lee 2000).

No data suggesting that competition for food is limiting populations. ENSO events and hurricanes decrease nesting success in some years (Duffy 1990; Schreiber 1996, 1997) but probably have little effect on adult survival. No data on adult survival, few data on reproductive success (see Measures of breeding activity, above). Adequate nest sites (free of disturbance and predators) are limiting (Schreiber 2000a). Population appears to be declining in the West Indies driven by human disturbance (Lindsey et al. 2000). No data on dispersal or ability to colonize new areas. Significant differences in egg size and adult size within Caribbean basin (Tables 1 and 2) indicate that birds do not move readily between areas and may not colonize new areas once extirpated (EAS).