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  • Tags / Keywords coconut palm
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  • Tags / Keywords brown rats
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Canna seabird recovery project: 10 years on
Island and Ocean Ecosystems, BRB
Available Online
2019
Rats were eradicated in 2005–2006 from the islands of Canna and Sanday, Scotland (total area 1,320 ha). Poison bait was laid from December 2005 onwards and the last rat was killed in February 2006. An intensive period of monitoring over the next two years con?rmed that no rats remained on the islands. Seabirds have been monitored on Canna for nearly 50 years and some species have shown good evidence of recovery since the eradication. Other species have not recovered and this may have been due to mortality caused by food shortages or storm events which have been impacting seabirds in the region. These regional changes in pressures affecting the seabird populations make the interpretation of the impacts of the rat eradication programme much more difficult. Atlantic puffins, formerly con?ned to off shore stacks, have recolonised sites on the mainland of Canna and a count of over 2,000 was recorded in 2016. Manx shearwaters, which had ceased nesting in the monitored colony have made a slow recovery to one or two pairs in 2016. Productivity has also increased from a low of 0.2 chicks per nest in the 1990s to 0.74 in 2017. European shags nesting in boulder colonies were most susceptible to rat predation. One such colony has recovered from 45 nests in 2005 to 75 in 2016 and productivity increased from less than 0.7 chicks per nest to an average of 1.6 following eradication. Populations of shags nesting in cliff locations have shown no recovery or have declined. Mew gulls, which nest along the shoreline, have increased from ?ve to over 30 pairs. Other seabirds, such as common guillemots and black-legged kittiwakes, have shown no clear trends and are probably affected by other factors. Rabbit populations have increased on both islands, reaching an estimated 15,500 animals in 2013 that were causing considerable damage through grazing, erosion, and disturbance of archaeological remains. It is unclear whether the increase in rabbit numbers can be attributed to rat eradication. An intensive control programme has brought the rabbit population under control. While some seabirds have responded positively to the rat eradication, the response of some has been slow and others have not responded, probably as a result of regional pressures on their survival. It is important that monitoring of both seabirds and rabbits continues to track the success of this important seabird colony.
Maximising conservation impact by prioritising islands for biosecurity
Available Online

Bambini, L.

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Dawson, J.

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Havery, S.

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John, L.

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Oppel, S.

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Radford, E.

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Varnham, K.

2019
Invasive alien species are one of the primary threats to native biodiversity on islands worldwide, and their expansion continues due to global trade and travel. Preventing the arrival and establishment of highly successful invasive species through rigorous biosecurity is known to be more economic than the removal of these species once they have established. However, many islands around the world lack biosecurity regulations or practical measures and establishing biosecurity will require social and financial investments. Guiding these investments towards islands where native biodiversity is at highest risk from potential invasions is of strategic importance to maximise conservation benefit with limited resources. Here we implement an established prioritisation approach, previously used to identify which islands will have the greatest conservation gains from the eradication of invasive species, to identify which islands would benefit the most from establishing or improving biosecurity. We demonstrate this approach for 318 islands in the Caribbean UK Overseas Territories and Bermuda where we considered all threatened native terrestrial vertebrates that are vulnerable to the most harmful invasive vertebrates (black and brown rats, cats, small Indian mongoose, green iguana). The approach calculates the increase in conservation threat score resulting from anticipated negative effects of potential invaders on native biodiversity, and highlighted Sombrero (Anguilla) and Cayman Brac (Cayman Islands) as important islands where threatened reptile species would likely be eliminated if rats, feral cats or mongoose invaded. Feasibility and cost implications should now be investigated more closely on the highlighted islands. The prioritisation presented here can be expanded to more islands and more invasive/native taxa (herbivores, plants and invertebrates), but requires a classification of the severity of potential impacts between invasive and native species for which currently little information exists. Besides highlighting opportunities for biosecurity, this approach also highlights where knowledge gaps about population sizes of and threats to reptiles with restricted ranges exist.
Report on results of rat control trials in the Tokelau Islands from 30 July to 20 September 1970 and recommendations for a comprehensive scheme of rat control
BRB
Available Online

Kazimierz Wodzicki

1970
The visit to the Tokelau Islands described below is the third carried out in a study of ecology, rat control and related problems. The first visit in 1966/67 (Wodzicki 1968 A) was devoted primarily to the study of the ecology of the Polynesian rat (Rattus exulans) and the environment, including the animals and the vegetation, of Nukunonu atoll. The main objects of the second expedition in April-June 1968 (Wodzicki 1968 B) were the initiation of a long-term investigation of rat damage on all three atolls and the training of two men from each island as rat control operatives. The present visit was planned with the following tow main objectives in mind: 1. the study of the relationship of rat damage to various coconut varieties growing in the Tokelau Islands; and 2. the conduct of rat control trials with the view of preparing for the Administrator, Tokelau Islands (Mr. Richard B. Taylor) recommendations for a rat control scheme suitable for the Tokelau Islands. The preliminary analysis of data collected during the fifteen months long investigation of rat damage in 1968/69 on the three atolls suggested that palms belonging to some varieties may be more prone to rat damage then others (Wodzicki 1970). It seemed important that we learn more about the character of palms growing on the three atolls. With regard to rat control, trials with various kinds of poisons have been carried out since our first visit to the Tokelaus in 1966/67 (Wodzicki 1968 A). However, during our first two visits knowledge of rat ecology was not sufficiently advanced to allow for more sophisticated tests. Since the author's 1968 visit, the important work on rat control in the Gilbert and Ellice Islands by F.J. Smith (Smith 1969) has become available. This information and our knowledge of rat ecology, gradually acquired since the beginning of the Tokelau Islands rat project, now makes possible a programme that could become the basis of a practical rat control scheme for the three islands. As most of the previous work had been carried out on Nukunonu atoll only, it was felt that half of the time during the visit should be spent on Fakaofo and th remainder on Atafu. Following a brief descrption of these trials is the writer's recommendation of a rat control scheme submitted to the Administrator, Tokelau Islands. Finally, some other observations on plants, animals and related aspects are friefly reported and collections made for the Botany Division, D.S.I.R. and the Dominion Museum are briefly mentioned.