Abstract
Seabirds are among the most threatened birds as a result of acute exposure to many anthropogenic threats. Their effective conservation requires a detailed understanding of how seabirds use marine habitats. Recently, one of the largest no-take marine reserves in the Atlantic was designated in tropical waters surrounding Ascension Island, on which the largest Atlantic population of sooty terns (Onychoprion fuscatus) breeds. Although they are the most abundant tropical seabird, they appear to have suffered marked population declines on Ascension Island as they have elsewhere. Here, we describe year-round movements and habitat use of male and female sooty terns between 2011 and 2015. On average, birds traveled 47,000 km during their 8 months of migration, during which they remained within 2,900 km of the island. They spent most of the day and night in flight, only touching down briefly on the ocean most likely to feed. Habitat suitability models successfully predicted foraging ranges of birds and their at-sea distributions varied considerably between seasons, years and sexes. Considerable variation in range overlap between birds and the new marine protected area (MPA) suggests that similar such studies of other marine taxa are urgently needed. The range of sooty terns mainly falls in the high seas outside of the new MPA, highlighting the very large areas that many oceanic seabirds forage across and the challenges their conservation present.
Highlights
Effective animal conservation first requires detailed knowledge of an organism’s spatial and temporal distributions
Seabirds are excellent bio-indicators of anthropogenic pressures on the marine environment (Furness and Monaghan, 1987). Their movements may reflect the distributions of other key elements of marine food webs (Phillips et al, 2009). This is especially true of tropical seabirds, many of which have near-obligate relationships with cetaceans and predatory fish such as tuna that drive prey species to the surface where seabirds feed on them (Veit and Harrison, 2017; Reynolds et al, 2019) in so called “facilitated foraging” (Maxwell and Morgan, 2013)
We considered the 50 and 95% kernel utilization distribution (UD) contours to represent the core foraging range (CFR) and the home range (HR), respectively
Summary
Effective animal conservation first requires detailed knowledge of an organism’s spatial and temporal distributions. Seabirds present conservationists with challenges in this regard in part because of their high mobility (Norris and Pain, 2002; Oppel et al, 2018) and extensive foraging ranges, when not breeding (Flint, 1991; Catry et al, 2009) In light of their perilous conservation status compared to other avian taxa (Votier and Sherley, 2017; Dias et al, 2019), characterizing seabird movements to inform conservation strategies is paramount, especially since many have undergone steep recent declines in population size worldwide (Croxall et al, 2012; Paleczny et al, 2015). Seabirds are excellent bio-indicators of anthropogenic pressures on the marine environment (Furness and Monaghan, 1987) Their movements may reflect the distributions of other key elements of marine food webs (Phillips et al, 2009). Understanding seabird movements is of high importance for planning and assessing the effectiveness of marine reserves (Lascelles et al, 2016; Anon 2018; Oppel et al, 2018)
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