Monday, 24 July 2017

Seychelles magpie robin population census on Denis Island, June 2017

A total of 76 individual Seychelles magpie robins were observed during a population census of the species on Denis Island from13-20 June 2017. Fifty seven of the robins observed were ringed and 19 were unringed.  In addition to censusing the population, 12 of the unringed robins were captured and ringed. A total of seven SMR were still unringed at the end of our time on Denis.

Following cat Felis catus and rat Rattus rattus eradications and rehabilitation of native broadleaved woodland habitat, twenty Seychelles magpie robins Copsychus sechellarum (SMR) were introduced to Denis Island in June 2008 as part of a national recovery programme for the species (Burt et al. 2016). For the first two years post translocation the robins were supplementary fed on a daily basis, but supplementary feeding ceased in 2010. Management currently involves the provision of nest boxes, ringing new recruits to the population, and to clearing relatively small areas of fouzer taba fern Nephrolepis biserrata to improve the foraging habitat for the robins within the forested conservation zone.
The purpose of this work was to (i) estimate the current SMR population size on Denis, (ii) map approximate territory locations and identify territory occupants and (iii) ring unringed SMR with metal ID ring and an individually identifiable colour combination.

Photo: Seychelles Magpie robin (KlartjeePuttemans)

The census was undertaken by Rachel Bristol and Indira Gamatis from 13-20 June 2017. All areas of the island were searched several times for SMR. All robins seen were identified i.e. ring combination recorded, and the number and age (adult/ juvenile-based on plumage) of unringed birds was also noted. The locations of individuals and group composition (i.e. who was hanging out with who) was also recorded.
Unringed robins were caught, ringed, measured and blood sampled. They were captured mostly using a spring trap baited with live termites, but also with a mist net using termites as an attractant.

Population size, trend and age structure
A total of 76 magpie robins were seen on Denis during this census. Two of the original robins translocated from Fr├ęgate Island are still present. These two males are a minimum of 10 years old as both were adults at the time of translocation to Denis in June 2008. Nineteen individuals, almost all of which were juveniles, were unringed. These 19 individuals represent productivity over the past year. The population trend is increasing, see Figure 1. We are confident this census is fairly accurate, however it is possible a few individuals were undetected, therefore this population estimate of 76 confirmed individuals can be considered conservative.

Figure 1. Trend in Magpie robin population size on Denis Island from introduction in 2008 till present
(Data sources: Burt et al. 2016; Denis Island magpie robin monitoring records; Bristol & Gamatis 2017)
Twelve robins were ringed during this census. Biometric measurements and blood samples were taken from all individuals ringed. Seven individuals were still unringed at the end of our time on Denis.

Photo: Magpie robin juvenile with new rings (R.Bristol)

Territories (location and number) appear to have changed little since the last accurate monitoring in 2016. There appear to be 18 territories on Denis each occupied by 2-6 robins. However we were not on the island for sufficient time to assign all individuals to territories with certainty, or to confirm possible shifts in territory boundaries.

Thank you as always to Green Islands Foundation (GIF) and Denis Island management for enabling this census and providing transport, accommodation and meals.

Bristol RM and Gamatis I (2017) Seychelles magpie robin population census on Denis Island, June 2017. Unpublished report.

Burt AJ, Gane J, Olivier I, Calabrese L, de Groene, A, Liebrick T, Marx D, Shah N (2016) The history, status and trends of the Endangered Seychelles Magpie-robin Copsychus sechellarum. Bird Conservation International 26, 505-523. doi: 10.1017/S0959270915000404.

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