Frigatebirds By Kristin Tollefson
Common Names: There are five species of frigatebirds in the world. Two live in the Galapagos Islands: the Great Frigatebird and the Magnificent Frigatebird. Frigatebirds got their name because their large wings are reminiscent of the sails on ships. They are also called Man ’O Wars because they steal food from other birds.
Scientific Names: Great Frigatebird Magnificent Frigatebird Kingdom: Animalia Animalia Phylum: Chordata Chordata Class: Aves Aves Order: Pelicaniformes Pelicaniformes Family: Fregatidae Fregatidae Genus: Fregata Fregata Species: minor magnificens
Nearest relatives: In addition to the great frigatebird and the magnificent frigatebird, there are three other species: the ascension frigatebird (Fregata aquila), the Christmas Island frigatebird (F. andrewsi), and the lesser frigatebird (F. ariel). Other members of the Pelicaniformes order include tropic birds, boobies, pelicans, cormorants, and anhingas. All of these birds are aquatic; anhingas are fresh-water birds, pelican and cormorants live in both fresh and salt water, and the other three groups are marine birds. Species of pelicans, tropic birds, boobies, and cormorants all live on the Galapagos Islands (Jackson, 1985).
Name in Spanish: Rabihorcado
Physical description: Frigatebirds are large, black birds, approximately the size of a hen. They can have wingspans of up to 7.5 feet. The tail of the frigatebird is forked, which allows it to maneuver very well in flight. Their beaks are hooked at the tip, which helps it to catch fish. Male frigatebirds have a red gular sac (at the throat) which they can inflate like a balloon. Great frigatebirds are difficult to distinguish from magnificent frigate birds. A table of differences follows: Great frigatebird Magnificent frigatebird Males Brown band across wings No brown bands Females White feathers on chin, throat, and breast White on throat and breast only Red eye ring Blue eye ring Juveniles White head with some rusty color on it White head (1 yr)
Island(s) where it lives: The great frigate bird nests on Tower Island and San Cristobal. The magnificent frigatebird is more common in the Galapagos, and nests on North Seymour and San Cristobal Islands. (Jackson, 1985)
Geographic range: Both the Magnificent and Great frigatebirds are found in most tropical oceans in the world. The magnificent frigatebird is found in the Caribbean, and along the coasts of north and south America. The great frigatebird is found in the Indian ocean, and the tropical parts of the Pacific ocean. (Rothman, 2007) (see maps on page 3) They have a very wide range because they spend most of their lives in the air. They fly using warm air thermal currents, to fly more efficiently. The Galapagos population (subspecies) of Magnificent frigatebirds is considered endemic to the islands.
Habitat: Frigatebirds are mostly pelagic, which means that they live over the open ocean. They breed and nest mostly on islands, where the threat of predators is less. They build nests in low shrubs and small trees (Rothman, 2007).
Abundance and density: The estimated world population of Magnificent Frigatebird is 200,000 individuals, based on a study from 2001. There are approximately 340,000 Great Frigatebirds. (Birdlife international, 2004) The only time the birds congregate is when breeding and caring for their young. In the Galapagos, they build nests together in colonies. One study measured a density of 0.06 nests/m2 for great frigatebirds in the Galapagos (Diamond, 1973)
Diet: Frigatebirds get their food in three ways: surface dipping, kleptoparasitism, and opportunism. For surface dipping, the birds fly over the surface of the ocean, and dip out fish. They are not able to land on the water because their feathers are not waterproofed enough. In a study in Isla Isabella, Mexico, Frigatebirds had a diet that consisted of 96.8% fish, 2.3% squid, and 0.9% crustaceans (Calixto-Albarran, 2000). Frigate birds can also get food by kleptoparasitism, which occurs when the frigate bird steals food from other birds. The frigatebird will fly close to a bird of a different species, such as a booby, and harass it until the other bird disgorges its food. Opportunism refers to the fact that frigate birds will take advantage of many food opportunities. They have been known to eat unattended chicks and sea turtle hatchlings. They have also become good at getting food from human activities, such as fishing boats.
Reproductive Ecology: Most of the papers on frigatebirds are studies of their breeding behavior. This is what makes frigate birds unique. Male frigate birds have red throat pouches. During breeding season, males puff out their throat pouches with air until they look like red, heart-shaped balloons. They also make clicking and drumming noises. The bigger the pouch, the deeper the drumming sound the bird makes (Madsen 2004). Great frigatebirds make a “gobble” sound, similar to a turkey, while magnificent frigatebirds make a “rattle” or “drum” sound (Rothman, 2007) Males also extend their wings and vibrate them to help attract attention. Female frigatebirds choose mates based on the size of the male’s red throat pouch. Females fly overhead, looking at the groups of males. When the female chooses one, she lands and makes corresponding twittering noises, and both she and the male will shake their heads. Frigate birds are monogamous each breeding season, and only lay one egg each season (Diamond, 1973) Males assist females in caring for the chick, until the chick is between 18 and 160 days old. After this period, the female cares for the chick alone until it reaches fledgling stage and leaves the nest. (Osorno 2004). Females sometimes continue to feed the chick several months after it leaves the nest. Because of the extensive care involved in raising a chick, frigate birds do not reproduce every year. (Rothman, 2007) However, they have very long life expectancies, so this reproductive strategy is efficient.
Symbioses: not found
Human impact on Frigatebirds: Since Frigatebirds are somewhat opportunistic, they have been able to find some new food sources because of human activities such as fishing. This helps their populations. However, humans have also introduced new species into the islands. Feral cats have been seen to attack frigatebirds (Konecny, 1987) and they also sometimes drive away adults, and eat eggs or chicks of nesting birds. Since frigatebirds, as well as many other native birds are not adapted to cope with land predators in the Galapagos, cats may become a problem in the future.
Map of the Range of the Great Frigatebird: retrieved from: www.bird- stamps.org/cspecies/1900400.htm
Map of the range of the Magnificent Frigatebird:
Magnificent Frigatebird: Great Frigatebird:
Works Cited BirdLife International 2004. Fregata magnificens. In: IUCN 2006. 2006 IUCN Red List of Threatened Species.