Habitat and ecology of breeding and non-breeding White-tailed Tropicbirds (Phaethon lepturus catesbyi) in Bermuda

Mejias, Miguel Alberto (2017) Habitat and ecology of breeding and non-breeding White-tailed Tropicbirds (Phaethon lepturus catesbyi) in Bermuda. Masters thesis, Memorial University of Newfoundland.

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Abstract

Pelagic seabirds have terrestrial and marine life stages and conditions at both sites can affect survival. On land, seabirds are threatened by destruction of nests and introduced predators. Assessments of threats at-sea, however, requires data on pelagic movement and behaviour, which is unknown for many seabirds. To mitigate degradation of breeding sites, artificial cavities are sometimes used. To identify pelagic activities geolocators (GLS) are a useful tool. However, data on nest-site selection, nest success and predation of artificial and natural seabird cavities are limited. In Bermuda, we monitored 158 natural and 178 artificial cavities of White-tailed Tropicbirds (Phaethon lepturus catesbyi) in 2013-2015. Tropicbirds favoured natural cavities with nesting sand, smaller entrances and on steeper cliffs. Artificial cavity occupancy varied by location, year and cavity depth. Clutch survival increased in deeper cavities, with smaller entrances and no rubble. Nestling survival varied by year and increased with age. American Crow (Corvus brachyrhynchos) predation was higher in natural cavities, and shallower cavities with larger entrances. We obtained GLS data from 25 recaptured tropicbirds in 2015 and learned that birds in the fall and winter ranged from Bermuda to the Mid-Atlantic Ridge. Non-breeders spent 95% of night periods and 59% of day periods wet. We found nest-cavity traits and temporal factors important for nesting tropicbirds. However, introduced rats were unaffected by cavity dimensions and should be removed. Lastly, we found, for the first time, marine areas where Atlantic tropicbirds are vulnerable and can be studied for pelagic threats.

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