| Summary: | Every autumn, migratory shorebirds move from their breeding grounds to their wintering areas. During the wintering season shorebirds need to find food, typically in intertidal flats uncovered by the receding tide, and when the tide rises, they move to resting areas, known as high-tide roosts. The Bijagós archipelago is one of the most important wintering areas in West Africa, hosting several hundred thousands of shorebirds, however the wintering ecology of these species in this site remains little studied. Although many studies have focused in the foraging ecology of these species, including some in the Bijagós, the information on habitat use, specifically regarding roosting areas, is mostly lacking. This thesis aims to determine the variation in shorebird use of tannes as high tide roost (a unique habitat to tropical areas) and to quantify the proportional usage of this habitat using satellite tracking of two shorebird species (Bar-tailed Godwit, Limosa lapponica and Whimbrel, Numenius phaeopus), in a major tropical wintering area, the Bijagós archipelago in Guinea-Bissau. Results indicate that tannes are mostly used by shorebirds around the high-tide peak, both during diurnal and nocturnal tides. During the peak high tide, when tannes often flood, shorebirds must find alternatives (such as mangroves), but many return soon after the flood peak, suggesting that tannes have an important role as resting habitats. Satellite tracking data indicated that intertidal flats were the most used habitat by both species, as could be expected, but that mangrove was the second most used habitat for the Whimbrel. Although tannes presented lower proportional use from the satellite tracking data, potentially associated with the characteristics of the two species tracked, camera trapping data indicated substantial numbers of shorebirds in some tannes. This is the case in the Ratum tanne, which congregated up to 657 individuals. These results suggest that protecting high-tide roost habitats such as tannes and mangroves in tropical ...
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