Breeding cavity-nesting seabirds on remote, oceanic islands are threatened largely by destruction of nest cavities and introduced predators. In response, artificial cavities are often implemented as a conservation strategy. Effective artificial cavity programs require recognition of specific nest-site characteristics, which can be major determinants of survival and persistence of cavity-nesting seabirds. In Bermuda, we monitored 158 natural and 178 artificial cavities of the White-tailed Tropicbird (Phaethon lepturus catesbyi) from 2013–2015 to determine if specific nest-site characteristics could explain cavity selection, nest survival, and predation by introduced rats (Rattus spp.) and the American Crow (Corvus brachyrhynchos). We found that tropicbirds preferred natural cavities lined with sand, and which had smaller entrances and were located on steeper cliffs. Occupancy of artificial cavities on the mainland varied across years and increased with cavity depth, whereas neither variable had any effect on artificial cavity occupancy on satellite islands. Clutch survival declined in cavities with rubble in nesting sand, and those with shallower cavity depths and larger entrance heights. Nestling survival varied by year, declined as the nesting season progressed, and increased with nestling age. Rat predation was significantly higher on mainland sites compared with satellite islands. Crow predation occurred only on offshore island sites, where natural cavities and shallower cavities with larger entrance heights were vulnerable. Rat and crow predation rates varied across years. Our results suggest multiple nest-site characteristics and temporal factors are important predictors of productivity in White-tailed Tropicbirds. Conservationists should simultaneously consider nest-cavity siting and dimensions, while they conduct biosecurity and predator control to improve the nest success of cavity-nesting seabirds.
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