It is a surface-feeder, feeding on fish, particularly Flying-fish Cypsilurus, Hirundichthyes and Exocoetus volitans, and newly hatched Green Turtles Chelonia mydas. Breeding occurs in four loose colonies (Orta 1992a), mainly on the summit plateau of Boatswainbird Island, especially on rougher areas with some groups of birds occupying ledges on the sides of the plateau (Ashmole et al. 1994). Since 2012 a new colony has formed on the south-west facing slope of Letterbox, a volcanic headland < 1 km from Boatswainbird Island. Over the past 4 years this colony has grown in size both in terms of number of breeding individuals (2 to >100) and also the area covered. Breeding is recorded year-round, but there is evidence of some seasonality with laying increasing from May and peaking in October, then declining to a minimum in February-April (Ashmole et al. 1994). Its clutch-size is one and breeding success is low (50:50). 

Fregata aquila breeds predominately on Boatswainbird Islet, a flat-topped, steep-sided rock, 250 m off the north-east coast of Ascension Island (St Helena to UK) in the Atlantic Ocean, but re-colonised the main island of Ascension in 2012 following successful cat eradication in 2006. Since the early 1800s, when it bred on Ascension Island itself, the population has suffered serious declines and, in 1997, was estimated to lie between 5,000-10,000 individuals (Pickup 1998). The most recent estimates for breeding and mature females are 6,250 and 9,341 respectively, based on census data from 2001-2002; suggesting c.18.682 mature individuals, assuming an equal sex ratio (Ratcliffe et al. 2008). Determining population trends for this species is problematic due to difficulties in carrying out census work, poor baseline information and the high number of mature non-breeders in the population (Pickup 1998, Ratcliffe 1999). However, the use of a 'virtual ecologist' model on recent census data, alongside historic data, point to a stable population (Ratcliffe et al. 2008). The small population that re-established on mainland Ascension in 2012 grew rapidly from 2 pairs in 2012 (of which 1 chick successfully fledged) to >100 pairs in 2016, and is expected to grow further as more birds re-distribute from Boatswainbird Island. At sea, the species forages generally within a 400-600 km radius around Ascension, but satellite tracking indicates use of the Atlantic Ocean to the coast of Brazil.

Conservation Actions Underway
Following the cat eradication programme, Ascension is maintained free of feral cats by enforcing a strict sterilisation regulation for all domestic cats, and by severely limiting the number of domestic cats that can be brought to the island, which are regulated through a cat registration database. Boatswainbird is a Sanctuary under local legislation (National Protected Areas Ordinance 2015), and the adjacent colony on Letterbox (also protected as a Nature Reserve under local legislation) is closely monitored. In 2016 the Ascension Island Government committed to protecting 50% of its Exclusive Fishing Zone as a marine sanctuary, excluding all commercial international fishing.

Conservation Actions Proposed
Use independent observers on longline vessels to investigate the numbers of this species killed (Ratcliffe 1999). Instigate measures to prevent future mortalities by long-lining if this is proven to be a threat (Ratcliffe 1999). Ensure sustainable use of the fisheries around Ascension Island (Ratcliffe 1999). Conduct further research on breeding behaviour of marked birds (Pickup 1998). Monitor changes in distribution, productivity and long-term population trends. Conduct educational awareness with local recreational fishers on how to safely release hooked birds.