Long-term monitoring of landbirds on Aldabra Atoll indicates increasing population trends

Abstract

SummaryLong-term survey data can provide important information on temporal and spatial changes in bird populations and are needed for conservation management. We investigate population indices of seven landbird species using an 11-year dataset from the UNESCO World Heritage Site of Aldabra Atoll. We analysed the associations of location, season and habitat with abundance, assessed population trends, and examined the influence of monitoring circumstances on results. Populations of all species except for the Aldabra Drongo Dicrurus aldabranus increased over this period. Abundance was associated with season and habitat, and interactions were found between season and location that differed for each species. Bird count results were affected by the timing of monitoring, number of observers and weather conditions. We use the results to review the strengths and weaknesses of the current monitoring programme and make recommendations for improvements. Overall our results indicate no immediate cause for conservation concern for the Aldabra landbird species monitored.

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“…It is home to the last remaining population of Indian Ocean giant tortoises 17 ( Aldabrachelys gigantea ) and provides one of the largest nesting sites for endangered green turtles ( Chelonia mydas ) 18 in the western Indian Ocean. The atoll supports large colonies of seabirds 19 , 11 endemic land-bird species/sub-species 20 and the biomass of fish and sharks in its extensive coral reef and mangrove ecosystems is among the highest in the Indian Ocean 21 . The ecosystem services that Aldabra and other Seychelles island ecosystems provide are vital to human health and prosperity in the Seychelles and across the wider region but have already been subject to intense pressure from invasive alien species 22 , 23 , habitat loss 24 and climate change 25 .…”