Abstract
Seabirds are a highly threatened group, yet the foraging ecology of several species remains poorly understood. Brown boobies breed in all oceans in the tropical region and are common across their range. In Tinhosa Grande (São Tomé and Príncipe), this species breeds in one of the largest colonies of seabirds in the east tropical Atlantic. We studied the foraging ecology of Brown boobies from this colony during the chick-rearing period. Thirty-three birds were tracked with GPS loggers and their diet was analysed from 11 regurgitations, using traditional and DNA barcoding techniques for prey identification. A total of 127 completed foraging trips were identified, 89% of which lasted less than 24 h. Females performed significantly longer trips and both sexes foraged preferentially over deep oceanic waters. The diet of Brown boobies included juvenile fish and squid (Sthenoteuthis pteropus), comprising mostly fish species whose juvenile phases live in the pelagic environment, and only migrate to coastal waters when adults. The most frequent of those prey found was Flying gurnard (Dactylopterus volitans). The relevance of such prey shows that Brown booby conservation depends not only on the management of their foraging areas and breeding sites but also on the correct management of the coastal adjacent areas that support the adult individuals of some of their prey. Our results suggest that the areas closest to the colony do not have available resources for these birds to feed on and that Brown boobies may be associate with subsurface marine predators or with sargassum patches to forage.
Highlights
Seabird populations are declining worldwide (BirdLife International 2018) mostly due to direct mortality, changes in food resources and marine ecosystem functioning and breeding habitat lost
A total of 127 trips were obtained from 28 birds, of which 14 trips lasted more than 24 h
Birds spent most of the nocturnal period sitting at sea, as assessed by the relatively fixed GPS positions
Summary
Seabird populations are declining worldwide (BirdLife International 2018) mostly due to direct mortality, changes in food resources and marine ecosystem functioning and breeding habitat lost. The family of seabirds comprising gannets and boobies, range from cold temperate seas to the tropics breeding mostly in offshore islands (Brown et al 1983, Hoyo et al 1996). Different species can forage in coastal waters or offshore, ranging from a few km to more than 500 km from the nesting sites Within Sulidae, there are three species of boobies that are pantropical, Brown booby (Sula leucogaster), Masked booby (Sula dactylatra) and Red-footed booby (Sula sula). These pantropical sulid species live in broadly similar environments and have comparable distributions (Hoyo et al 1996)
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