Abstract
The South Pacific Gyre has the most hyper-oligotrophic waters in the world and is considered the largest “oceanic desert.” Rapa Nui (Easter Island), located within the South Pacific Gyre, is a breeding ground for masked boobies (Sula dactylatra), which are seabirds with a foraging range that effectively confines them within the gyre. The foraging ecology of this species in the gyre was examined by attaching GPS and time-depth devices to chick-rearing adult birds (9 and 14 birds in 2016 and 2017, respectively) and by collecting regurgitates (18 and 15 samples in 2016 and 2017, respectively). In addition, the birds’ foraging ecology between years was compared. Masked boobies traveled in various directions, dived at unspecific locations, and explored areas < 110 km from the colony. Local environmental conditions were not significantly different between years, and differences in foraging parameters (maximum foraging range, trip duration, and dive depth) were greater among individuals than between years. The foraging characteristics of masked boobies suggest that resources were ephemerally distributed around the colony, with similar abundances across years. Under these conditions, traveling to unspecific locations may increase the area covered and the probability of prey encounter. The spatial and temporal consistencies in environmental conditions explain the uniformity of foraging parameters between years. The ability of masked boobies to exploit ephemerally distributed resources in seascapes like Rapa Nui may help explain its pantropical distribution.
Highlights
Optimal foraging theory suggests that predators make foraging decisions that optimize energy intake with minimal energy investment, maximizing energetic gain (Charnov 1976; Pyke et al 1977; Louzao et al 2014)
In the tropical marine environment, prey can be concentrated in areas of enhanced primary productivity [high chlorophyll-a concentration (CHL) and lower sea-surface temperature (SST)] (Ballance et al 2006), and seabirds may travel directly to these areas where prey encounters are likely to be higher (Weimerskirch 2007; Assali et al 2017)
The current study provides the first description of the foraging ecology of a plunge-diving seabird species in the hyper-oligotrophic waters of the South Pacific Gyre
Summary
Optimal foraging theory suggests that predators make foraging decisions that optimize energy intake with minimal energy investment, maximizing energetic gain (Charnov 1976; Pyke et al 1977; Louzao et al 2014). In the tropical marine environment, prey can be concentrated in areas of enhanced primary productivity [high chlorophyll-a concentration (CHL) and lower sea-surface temperature (SST)] (Ballance et al 2006), and seabirds may travel directly to these areas where prey encounters are likely to be higher (Weimerskirch 2007; Assali et al 2017). The South Pacific Gyre may be an especially challenging region for seabirds. This region has the most hyper-oligotrophic superficial waters in the world (Claustre et al 2008) and is considered to be the world’s largest “oceanic desert” (Morel et al 2010). While some seabird species breeding within the gyre, such as petrels, travel thousands of kilometers to forage at fronts with high productivity (Clay et al 2017), other species with smaller
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