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Using playback to estimate the distribution and density of the world’s smallest flightless bird, the Inaccessible Island Rail Atlantisia rogersi

Published online by Cambridge University Press:  24 August 2020

BEN J. DILLEY Open the ORCID record for BEN J. DILLEY [Opens in a new window] ,
GEORGE SWAIN ,
JULIAN REPETTO  and
PETER G. RYAN Open the ORCID record for PETER G. RYAN [Opens in a new window]
BEN J. DILLEY*
Affiliation:
FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, University of Cape Town, Rondebosch 7701, South Africa.
GEORGE SWAIN
Affiliation:
Tristan Conservation Department, Edinburgh of the Seven Seas, Tristan da Cunha, United Kingdom.
JULIAN REPETTO
Affiliation:
Tristan Conservation Department, Edinburgh of the Seven Seas, Tristan da Cunha, United Kingdom.
PETER G. RYAN
Affiliation:
FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, University of Cape Town, Rondebosch 7701, South Africa.
*
Author for correspondence; email: dilleyben@gmail.com
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Summary

The Inaccessible Island Rail Atlantisia rogersi, the world’s smallest extant flightless bird, is endemic to Inaccessible Island, a 14-km2 uninhabited island in the Tristan da Cunha archipelago, central South Atlantic Ocean. Rail populations are notoriously hard to survey and the rugged topography of Inaccessible Island makes a survey particularly challenging. Fortunately, Inaccessible Island Rails are very vocal, because their secretive behaviour means birds are hard to observe in the dense vegetation. We assessed the distribution of rails across Inaccessible Island using playbacks at 350 point-count sites in October–November 2018. Rail calls were heard at 98% of sites and we estimate the rail population to be in the order of 10,300 birds (95% CI 9,100–12,200), based on estimated rail densities in the six main habitats. Historic population estimates were reasonably crude and thus not suitable for inferring population trends, but the population appears to be stable and we recommend the species’ status remains as ‘Vulnerable’. The accidental introduction of alien mammals poses the greatest threat to the survival of the Inaccessible Island Rail and the removal of house mouse Mus musculus and ship rat Rattus rattus from neighbouring Tristan da Cunha Island would greatly reduce the risk of such a catastrophe.

Keywords

Atlantisia rogersiTristan da Cunha archipelagoflightless birdpoint countplayback survey
Type
Research Article
Information
Bird Conservation International , Volume 31 , Issue 2 , June 2021 , pp. 286 - 292
Copyright
© The Author(s), 2020. Published by Cambridge University Press on behalf of BirdLife International

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