Justification of Red List Category
This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Del Hoyo et al. (1992) estimated the population at several hundred thousand individuals, tentatively placed here in the range 100,000-499,999 individuals, although this could be an underestimate.
The population trend is increasing in North America (based on BBS/CBC data: Butcher and Niven 2007).
This species is distributed on the Pacific and Atalantic coasts of America, from California (USA) to Ecuador (including the Galapagos), and from Florida to south Brazil. One relict population breeds at Cape Verde off the coast of Africa. Outside the breeding season it is largely sedentary, with the dispersal of immature and non-breeding individuals.
The Magnificent Frigatebird often nests in mangroves, but also in bushes and even on cactus. It can breed on the ground (del Hoyo et al. 1992). Data reveals it is almost continuously on the wing, with morphology and flight pattern resulting in extremely low costs of foraging, relying on prey driven to the surface by underwater predators such as tuna. Low cost of flight due to extensive use of thermals allows exploitation of tropical waters in which prey is scarce (Weimerskirch et al. 2003). It feeds mainly on flying-fish and squid, but also jellyfish, baby turtles, seabird eggs and chicks, offal and fish scraps (del Hoyo et al. 1992).
Hunting likely occurs at numerous breeding sites, causing slow but significant population declines. The sub-population of Cape Verde has decreased to the point of extinction following persecution by fishermen (Orta et al. 2018). Development of commercial and domestic areas in the Caribbean is responsible for local declines in populations and their breeding success, alongside the loss of coastal roosting sites that are vitally important to the species as it does not rest on water during the day. These developments have not yet been documented to have adverse effects on the total population. After unexpected high rates of nest failure following bird handling, the impact of different sampling methods on nest success were tested and revealed that wing tags have a substantial negative effect on pre-fledging nest success (Trefry et al. 2013).
Text account compilers
Calvert, R., Bennett, S., Ekstrom, J., Butchart, S., Martin, R., Fjagesund, T.
BirdLife International (2020) Species factsheet: Fregata magnificens. Downloaded from http://www.birdlife.org on 26/11/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 26/11/2020.