Synthesis of oystercatcher conservation assessments: general lessons and recommendations
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26 August 14
Bruno J. Ens, Les G. Underhill
This chapter synthesizes the information in the conservation assessments of the various oystercatcher species and subspecies. The Canary Island Oystercatcher Haematopus meadewaldoi went extinct in about 1940, leaving 11 surviving oystercatcher species. Between two and five subspecies are recognized for three species of oystercatcher, making a total of 18 surviving taxa (excluding buturlini as a separate subspecies of the Eurasian Oystercatcher).
The volume and quality of information available on the feeding ecology, life history, population size and trends, conservation status and threats, are highly variable between the various (sub)species. Whereas the nominate subspecies ostralegus of the Eurasian Oystercatcher Haematopus ostralegus is the best studied shorebird in the world, hardly any information is available on some other (sub)species.
All oystercatcher species are long-lived and dependent on coastal habitats during the non-breeding season. Many species and populations are coastal throughout the year, but some populations of some species move inland to breed. Oystercatchers breed on the open ground, making nests and chicks vulnerable to flooding, predation and destruction by human activities. ‘Black’ oystercatcher species are generally found on rocky shores, while ‘pied’ species are more often found on beaches, sandy shores, muddy coasts and estuaries. The current IUCN Red List of Threatened Species (IUCN 2013) only addresses the conservation status of oystercatcher species, not subspecies or subpopulations. Many subspecies have disjunct geographical distributions, so that if the subspecies went extinct, the empty area would not be re-occupied quickly by another subspecies. Furthermore, some subspecies have small population sizes. Indeed, the Chatham Oystercatcher Haematopus chathamensis has been classified as ‘Endangered’ since 1994 because of its small population size. We suggest that the subspecies galapagensis of the American Oystercatcher Haematopus palliatus should be classified as ‘Endangered’ and the subspecies frazari of the American Oystercatcher as ‘Vulnerable’ because of their small population sizes. The subspecies osculans of the Eurasian Oystercatcher should be classified as ‘Near Threatened’. IUCN may wish to consider revising the classification of the American Black Oystercatcher to ‘Near Threatened’ from ‘Least Concern’, but clear declines or fluctuations of population and distribution have not been demonstrated.
Coastal development and human activities in the coastal zone are the most important threat to oystercatcher species around the world under present conditions. Increasing human use of the coastal zone in combination with sea-level rise may well be the greatest threat in the future.