Camera trapping and transect counts yield complementary insights into an endangered island endemic rail

Abstract

Island endemic species are disproportionately represented in the tally of global extinctions. The island endemic Cocos buff-banded rail (Hypotaenidia philippensis andrewsi) is classified under the Australian Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) as Endangered. It is restricted to the remote Cocos (Keeling) Islands in the Indian Ocean where, until 2013, only the island Pulu Keeling supported a population of this species, following earlier extirpations of the bird from islands in the southern atoll. To establish a second viable population to mitigate against potential extinction of this subspecies, 39 rails were reintroduced from Pulu Keeling to Horsburgh Island in April 2013. As a component of post-translocation monitoring, we conducted intensive camera trapping from 29 May 2015 to 30 June 2016 (397 calendar days) to investigate recruitment success, behaviour and potential threats to the population. Biannual transect sampling to monitor and investigate long-term population density was also conducted. We found Cocos buff-banded rail persisting on Horsburgh Island with an increase in the founder population to 97 rails in February 2016. Ongoing recruitment with breeding activity on Horsburgh Island and the emigration of rails to nearby (2.5km) Direction Island is indicative of short-term success. Images from the camera traps have documented behaviours that have not previously been described for the species. House mice were also identified as a potential threat to the Horsburgh Island rail population. Island rail species have suffered a high rate of extinctions, and their conservation remains a formidable challenge, given the risks of continuing introductions of invasive mammalian predator species.