Conserving islands and their birds
Oceanic islands hold a disproportionately large amount of terrestrial biodiversity, yet are extremely vulnerable to introduced species: more than 90% of recent bird extinctions have been of island birds. Fortunately, eradicating invasive species can restore island ecosystems, provided there are strict controls on the subsequent import of people and materials. Birds are flagships for the conservation-management and restoration of island ecosystems. Our work focusses on South Africa’s Prince Edward Islands and the UK Overseas Territory of Tristan da Cunha and Gough Island.
This programme is mainly concerned with the impacts of introduced predators, especially House Mice Mus musculus, but also is involved in the eradication or control of introduced plants and invertebrates. The impacts of House Mice on seabirds were only discovered in the early 2000s, following research by Fitz students in collaboration with the Royal Society for the Protection of Birds (RSPB) at Gough Island. Since then, mice have been found to attack seabirds on Marion Island, and plans are underway to try to eradicate the species at both islands. Following a busy year for this project in 2018, when field work was conducted at Marion, Inaccessible and Nightingale Islands, 2019 was a year of consolidation, writing up papers, pushing forward on the policy front, and preparing for the next stage of field interventions.
Activities in 2019
- Two papers were published on Tristan Thrushes Turdus eremita, one revising population estimates for the species at Inaccessible and Nightingale Islands, and one on their consumption of intertidal invertebrates. The former paper used two different techniques (nest mapping and resightings of individually colour-marked birds) to conclude that the populations at the uninhabited Tristan islands are substantially larger than previously thought.
- A paper on the distribution and relative abundance of the Inaccessible Island Rail Atlantisia rogersi was submitted, showing that the species remains common throughout Inaccessible Island, and its population size is at least as large as that estimated in the early 1980s.
- A paper on the ongoing spread and rapid increase in impact of the introduced Soft Brown Scale Coccus hesperidium and its associated Sooty Mould Seiridium phylicae on Phylica arborea trees at both Inaccessible and Nightingale Islands was drafted. Because the fruit of these trees are crucial for the large-billed finches on these islands, the findings prompted the RSPB to investigate the viability of a biocontrol programme to limit the populations of Soft Brown Scale using parasitic wasps.
- Three years of mark-recapture data for Wilkins’ Nesospiza wilkinsi and Nightingale Finches N. questi collected by Ben Dilley and Delia Davies on Nightingale Island from 2016 to 2018 were analysed in collaboration with Res Altwegg (SEEC) to estimate first year and adult survival. These data were then used in a PVA exercise by the Conservation Biology MSc class to assess the possible impacts of reduced Phylica fruit load on the tiny population of Wilkins’ Finches confined to Nightingale Island.
- The programme to attempt to eradicate introduced House Mice from Gough Island, originally planned for winter 2019, was postponed until 2020. The plans for a follow-up eradication attempt to eradicate mice from Marion Island are also delayed until at least 2021. Peter Ryan remains involved in the planning for both attempts.
- Post-doc Susan Miller analysed genetic microsatellite data from Greg McClelland’s PhD to explore population structure among Lesser Sheathbills Chionis minor at the Prince Edward Islands. She found that Prince Edward Island sheathbills nested within the diversity of sheathbills from Marion Island, being similar to birds from the north coast of Marion. This result suggests that genetic differentiation among the two island populations is trivial, and thus Prince Edward can be used as a rescue population for Marion Island should a large proportion of the sheathbills on Marion be killed during the mouse eradication attempt.
- Autumn surveys were conducted for the fifth successive year to monitor the spread of mouse attacks on large chicks of Grey-headed Thalassarche chrysostoma and sooty albatrosses Phoebetria spp. at Marion Island.
- A paper on confirming the impacts of Black Rats Rattus rattus on a colony of Broad-billed Prions Pachyptila vittata breeding in a coastal cave at Tristan da Cunha was drafted. Rat predation of seabirds’ eggs and chicks is thought to be largely responsible for the low densities of burrow-nesting petrels at Tristan compared to other islands in the archipelago.
- Peter Ryan had the chance to visit the Pitcairn Islands in the central South Pacific in Oct-Nov 2019. Although his work focused on marine plastic pollution, he was able to gain useful insights into the biodiversity challenges faced by this UK Overseas Territory that shares many similarities to the Tristan archipelago.
- Ben Dilley was awarded his PhD on the impacts of mice on seabirds at Marion and Gough Islands. He remained at the Fitz writing up papers from his subsequent research at the Tristan archipelago.
- Andy Schofield (RSPB) put in a funding application to the Darwin Fund to support a three-year project to instigate biocontrol measures against Soft Brown Scale at the Tristan archipelago. Irrespective of the outcome of this funding, Dr Chris Malumphy, an entomologist specialising in the control of plant pests from Fera Science Limited, UK, will visit Tristan in early 2020 to assess the feasibility of using wasps to control Soft Brown Scale at the islands.
- Peter Ryan contributed to a global review paper in PLoS ONE identifying priority islands for restoration through eradication of introduced predators, led by Nic Holmes from Island Conservation.
- Chris Jones submitted a paper summarizing population trends in the Critically Endangered Gough Bunting Rowettia goughensis based on transect counts and territory mapping during the breeding season. The results suggest that the species is holding its own in the highlands of Gough, as the population has remained stable for the last decade or so.
Agreement on the Conservation of Albatrosses and Petrels; BirdLife International; DST-NRF CoE grant; EU-BEST; Royal Society for the Protection of Birds; South African National Antarctic Programme; UK Overseas Territories Environment Programme.
Prof. Peter Ryan (FIAO, UCT)
Dr Alex Bond (formerly at the RSPB)
Dr Richard Cuthbert (formerly at the RSPB)
Dr Ben Dilley (FIAO, UCT)
Trevor Glass (Tristan Conservation Department)
Dr Stefan Oppel (RSPB)
Dr Susan Miller (FIAO, UCT)
Andy Schofield (RSPB)
Dr Ross Wanless (FIAO, UCT and BLSA)
Research assistants: Chris Jones, Michelle Risi and Alexis Osborne (Gough 2018/19 and 2019/20).