Abstract
The Sooty Shearwater Ardenna grisea, an abundant but declining petrel, is one of many seabird species that construct breeding burrows, presumably because these confer protection from predators and the elements. Little is known about the causes of variation in Sooty Shearwater burrow architecture, which can differ markedly both within and between breeding sites. We hypothesize that burrow architecture varies in response to habitat type and competition for space. To address these hypotheses, we recorded Sooty Shearwater burrow dimensions on Kidney Island, the largest Sooty Shearwater colony in the Falkland Islands, South Atlantic, and modelled these as functions of burrow density (a proxy for competition) and habitat indices. Our models suggest that Sooty Shearwaters burrow further underground in response to competition for breeding space, and that soil underlying dense tussac grass Poa flabellata is more easily excavated than other substrates, indicating how vegetation restoration could aid the conservation of this species.
Highlights
The Sooty Shearwater Ardenna grisea, an abundant but declining petrel, is one of many seabird species that construct breeding burrows, presumably because these confer protection from predators and the elements
Little is known about the causes of variation in Sooty Shearwater burrow architecture, which can differ markedly both within and between breeding sites
Our models suggest that Sooty Shearwaters burrow further underground in response to competition for breeding space, and that soil underlying dense tussac grass Poa flabellata is more excavated
Summary
The Sooty Shearwater Ardenna grisea, an abundant but declining petrel, is one of many seabird species that construct breeding burrows, presumably because these confer protection from predators and the elements. Our models suggest that Sooty Shearwaters burrow further underground in response to competition for breeding space, and that soil underlying dense tussac grass Poa flabellata is more excavated. It is likely that burrow characteristics vary with habitat, such as vegetation, slope, soil structure or type, as these will affect both the energetic cost of excavation and the structural and hydrological properties of the burrow (Ramos et al 1997, Powell et al 2007) Neither of these hypotheses has been tested. Burrows at Putauhinu Island, New Zealand, are on average 0.5 m longer (McKechnie et al 2007) than those at Tıtı Island, New Zealand (Geary et al 2014) It is not known whether this is due to differences in habitat or competition. Understanding the drivers of variation in burrow architecture could inform habitat restoration projects as well as studies on competition and nutrient cycling by seabirds
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