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On the verge of a biological crisis: the state of invasive species in the Pacific

Island and Ocean Ecosystems, BRB

Available Online

Cas Vanderwoude

A report prepared by the Invasive Partnership for the Pacific Islands Forum Leaders Meeting, Palau July 2014 as requested by the Micronesian Chief Executives in Resolution 19-01

Canna seabird recovery project: 10 years on

Island and Ocean Ecosystems, BRB

Available Online

Rats were eradicated in 20052006 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.

Dawson, J.

Havery, S.

John, L.

Oppel, S.

Radford, E.

Varnham, K.

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.

The Ecology of Rodents in the Tonga Islands

Available Online

Twibell, John

The influence on crop damage of Rattus norvegicus, Rattus rattus, and the native Polynesian rat, Rattus exulans, was studied during the establishment of a rat control program for the Tongan Department of Agriculture in 1969. This was the first long-term study of Tongan rodents. Previous scientific literature on Tongan mammals is very sparse. The Kingdom of Tonga, or Friendly Islands, consists of approximately 150 small islands with a combined area of about 256 square miles at lat 21 0 S. The majority of these islands are composed of raised coral limestone ; however, there is a row of six volcanic islands on Tonga's western border. Tongatapu, the location of the government center, is the largest and most important island. The Ha'apai island group lies 80 miles north of Tongatapu, and 150 miles north is the Vava'u group. Fiji is 420 nautical miles east and Samoa is 480 miles north. The climate is tropical and is influenced seasonally by trade winds. Since Captain Cook's first visit in 1773, Western civilization has brought trade, missionaries, and perhaps rats to Tonga. With this shipping came numerous introduced plants and animals. The arrival dates for the common rat, Rattus norvegicus, and the "European" roof rat, Rattus rattus, are not known, but are believed to be more recent, probably since the increase of regular shipping trade and the construction of wharves. Presently rodents account for approximately 20 percent of the agricultural losses and $50,000 worth of economic loss each year (Twibell, unpublished). This is a conservative estimate based on damage counts and observation. In some areas rats destroy or damage up to 50 percent of the coconuts, which represent the main economic crop in Tonga. THE INFLUENCE on crop damage of Rattus norvegicus, Rattus rattus, and the native Polynesian rat, Rattus exulans, was studied during the establishment of a rat control program for the Tongan Department of Agriculture in 1969. This was the first long-term study of Tongan rodents. Previous scientific literature on Tongan mammals is very sparse. The Kingdom of Tonga, or Friendly Islands, consists of approximately 150 small islands with a combined area of about 256 square miles at lat 21 0 S. The majority of these islands are composed of raised coral limestone ; however, there is a row of six volcanic islands on Tonga's western border. Tongatapu, the location of the government center, is the largest and most important island. The Ha'apai island group lies 80 miles north of Tongatapu, and 150 miles north is the Vava'u group. Fiji is 420 nautical miles east and Samoa is 480 miles north. The climate is tropical and is influenced seasonally by trade winds. Since Captain Cook's first visit in 1773, Western civilization has brought trade, missionaries, and perhaps rats to Tonga. With this shipping came numerous introduced plants and animals. The arrival dates for the common rat, Rattus norvegicus, and the "European" roof rat, Rattus rattus, are not known, but are believed to be more recent, probably since the increase of regular shipping trade and the construction of wharves. Presently rodents account for approximately 20 percent of the agricultural losses and $50,000 worth of economic loss each year (Twibell, unpublished). This is a conservative estimate based on damage counts and observation. In some areas rats destroy or damage up to 50 percent of the coconuts, which represent the main economic crop in Tonga.

Predation pressures on sooty terns by cats, rats and common mynas on Ascension Island in the South Atlantic

Island and Ocean Ecosystems, BRB

Available Online

Dickey, R.C.

Hughes, B.J.

Reynolds, S.J.

Despite the presence of invasive black rats (Rattus rattus), common mynas (Acridotheres tristis), and feral domestic cats (Felis catus), sooty terns (Onychoprion fuscatus) breed in large numbers on Ascension Island in the tropical South Atlantic Ocean. These introduced predators impact the terns by destroying eggs or interrupting incubation (mynas), eating eggs (mynas and rats), eating chicks (rats and cats), or eating adults (cats). Between 1990 and 2015, 26 censuses of sooty terns and five of mynas were completed and myna predation was monitored on 10 occasions. Rat relative abundance indices were determined through trapping around the tern colonies and rat predation was monitored by counting chick carcasses. Cat predation was quantified by recording freshly killed terns. Prior to their eradication in 2003, cats had the greatest impact on sooty terns and were depredating 5,800 adults and 3,600 near-fledging chicks (equivalent to the loss of 71,000 eggs) each breeding season. We estimated that 26,000 sooty tern eggs (13% of all those laid) were depredated by approximately 1,000 mynas. Rats were not known to depredate sooty terns prior to cat eradication but in 2005, 131 of 596 ringed (monitored) chicks (22%) were depredated by rats. In 2009 chick carcass density was 0.16 per m2. Predation by rats hugely increased in the absence of cats and was the equivalent of 69,000 eggs. Care is needed when applying our findings to seabirds globally. The scarcity of alternative food sources and seasonally high density of easily available prey in the sooty tern colony may have magnified predation by cats, rats and mynas.

The Isles of Scilly seabird restoration project: the eradication of brown rats (Rattus norvegicus) from the inhabited islands of St Agnes and Gugh, Isles of Scilly

Island and Ocean Ecosystems, BRB

Available Online

Bell, E.

Boyle, D.

Buckley, P.

Floyd, K.

Garratt, W.

Lock, L.

Mason, S.

McCarthy, R.

Pearce, J.

Pearson, J.

St Pierre, P.

Sugar, K.

As part of the Isles of Scilly Seabird Recovery Project, and directed by Wildlife Management International Ltd, the eradication of brown rats (Rattus norvegicus) from the inhabited islands of St Agnes & Gugh, Isles of Scilly was completed between October 2013 and April 2014 with the assistance of volunteers, and staff from the Royal Society for the Protection of Birds, Isles of Scilly Wildlife Trust and Natural England. Bait stations with cereal-based wax blocks containing bromadiolone at 0.005% w/w were established on a 4050 metre grid over the island. With the presence of 85 residents on the 142 ha islands, this is the largest community-based brown rat eradication globally to date. Given the fact that a community is based on these islands, community engagement and advocacy was a vital and fundamental part of the eradication. Consultation for eradication began three years prior to the operation to explain the requirements for the proposed project and to assess support, but this built on many years of wider community engagement with seabird conservation. All of the residents supported the eradication of rats and vision of the project. The consultation and inclusion of the community in decision-making and management of the Isles of Scilly Seabird Recovery Project was a critical part of the operation and key to the success of the eradication. The community took ownership of the project and has committed to the on-going biosecurity requirements following the eradication of rats. The removal of brown rats from St Agnes and Gugh was a major achievement and provided the opportunity to restore the islands' communities of seabirds and other native species. This project provided an example of the effectiveness of ground-based rodent eradication techniques on an inhabited island and the lessons learnt during this operation can be used to help proposed eradications on other islands with communities and with terrain suitable for ground-based techniques.

Simultaneous rat, mouse and rabbit eradication on Bense and Little Bense Islands, Falkland Islands

Island and Ocean Ecosystems, BRB

Available Online

Carey, P.W.

Bense and Little Bense Islands (144 ha total area) have, for over a century, supported populations of three introduced pest mammals: Norway rat (Rattus norvegicus), house mouse (Mus musculus), and European rabbit (Oryctolagus cuniculus). An operation to eradicate these mammals simultaneously was undertaken in winter 2016. Cereal pellets laced with brodifacoum (25 ppm) were hand-broadcast on both islands in two applications with 3,900 kg of bait applied in total. Baiting transects were spaced at 20 m intervals and bait-throwing positions located every 20 m along each transect. The coastline was also baited at 20 m intervals. Precision bait coverage was aided by programming GPS units to give off an audible alarm when staff reached each correct bait-throwing position. Application 1 resulted in an average bait density of 15.3 kg/ha. Application 2 commenced 10 days later and resulted in an average baiting density of 11.7 kg/ha. Reduced availability of fi eld staff resulted in coverage in Application 2 being less complete than in Application 1 and only the most important mammal habitats were baited a second time. These were: all tussock areas, all coastlines, and some inland heath areas. Areas with no vegetation (e.g. burned zone on Bense) and some inland heath communities were not treated, although all of these retained unconsumed bait from Application 1. Some non-target mortality was recorded, with dolphin gulls (Larus scoresbii) being the most common victims. This was also the only species observed to consume bait pellets. Consumption of poisoned mammals or gulls may have killed three turkey vultures (Cathartes aura jota), one striated caracara (Phalcoboenus australis), and one short-eared owl (Asio flammeus). The removal of invasive species is part of a broader ecological restoration plan for these islands and will hopefully lead to an increase in native biodiversity, including the re-establishment of the endemic passerines Cobbs wren (Troglodytes cobbi) and blackish cinclodes (Cinclodes antarcticus).

Long term rodent control in Rdum tal-Madonna yelkouan shearwater colony

Island and Ocean Ecosystems, BRB

Available Online

Cabello, J.S. Santiago

Lago, P.

Varnham, K.

Rodent predation on eggs and chicks is one of the main threats to procellariiform species in the Mediterranean, where the black rat (Rattus rattus) and brown rat (R. norvegicus) have been present on many islands for centuries. The yelkouan shearwater (Puffinus yelkouan) is an endemic Mediterranean seabird species classified as vulnerable. Malta holds up to 10% of the global population; the largest colony, Rdum tal-Madonna (RM), protected as a Natura 2000 site, hosts around 500 breeding pairs. This colony has been monitored since its discovery in 1969. A very low reproductive success due to rat predation was noticed in the late 1990s to early 2000s. In 2007 a seasonal rodent control programme was established during the breeding season of yelkouan shearwater to reduce rat predation on eggs and chicks. Rodent control took place between 2007 and 2010 and was reviewed and continued from 2012 to 2017. Breeding success since 2007 has been higher than 80%. In two other colonies with rat presence and where rodent control did not take place, the breeding success in 2016 and 2017 was substantially lower than in the colony with the rodent control programme. The European storm-petrel (Hydrobates pelagicus melitensis) only breeds in rat-free areas like remote sea caves or islets around the Maltese islands. In 2014, the first breeding attempt by European storm-petrel was recorded on the Maltese mainland at RM with a chick fledging successfully for the first time in 2016. The ongoing LIFE Arcipelagu Garnija project is assessing rat predation in all Maltese yelkouan shearwater colonies in order to establish predator control in the most important yelkouan shearwater breeding sites in 2018.

The effect of Norway rats on coastal waterbirds of the Falkland Islands: a preliminary analysis

Island and Ocean Ecosystems, BRB

Available Online

Kuepfer, A.

Passfi eld, K.

Poncet, S.

Tabak, M.A.

The Falkland Islands have been affected by anthropogenic-induced habitat modifi cation including introduction of invasive species and grazing by livestock. Introduced Norway rats are known to have a large effect on native Falklands passerines but their effect on other native birds has not been explored. We investigated the effects of several environmental variables, including the presence of Norway rats and chronic grazing by livestock, on an assemblage of 22 species of coastal waterbirds by comparing species richness and relative abundance of birds among 65 rat-infested islands, 29 rat eradicated islands and 76 historically rat-free islands. Bird count data from 299 km of coastline were used to estimate relative bird abundance, expressed as the number of individuals per kilometre of coastline for each species. Our study provided three key results. First, coastal waterbird abundance on islands historically without rats was twice as high as that on islands where rats were present. Second, bird abundance on rat-eradicated islands was intermediate between that of historically rat-free and rat-infested islands. Third, habitat modification by grazing appeared to reduce bird abundance in both rat-free and rat-infested habitats. From a conservation perspective, this study suggests that rat eradication programmes in the Falkland Islands are effective at restoring coastal waterbird abundance and would be even more so if carried out in conjunction with restoration of native coastal plant communities.

Applying lessons learnt from tropical rodent eradications: a second attempt to remove invasive rats from Desecheo National Wildlife Refuge, Puerto Rico

Island and Ocean Ecosystems, BRB

Available Online

Figuerola-Hernandez, C.E.

Griffiths, R.

Herrera-Giraldo, J.L.

Howald, G.R.

Keitt, B.

Silander, S.

Swinnerton, K.

Will, D.J.

The introduction of invasive rats, goats, and rhesus macaques to Desecheo National Wildlife Refuge, Puerto Rico led to the extirpation of regionally signifi cant seabird colonies and negatively impacted plant and endemic reptile species. In 2012, following the successful removal of goats and macaques from Desecheo, an attempt to remove black rats using aerially broadcast rodenticide and bait stations was unsuccessful. A review of the operation suggested that the most likely contributors to the failure were: unusually high availability of alternative foods resulting from higher than average rainfall, and insufficient bait availability. In 2016, a second, successful attempt to remove rats was conducted that incorporated best practice guidelines developed during a workshop that focused on addressing the higher failure rate observed when removing rats from tropical islands. Project partners developed a decision-making process to assess the risks to success posed by environmental conditions and established go/no-go decision points leading up to implementation. Observed environmental conditions appeared suitable, and the operation was completed using aerial broadcast of bait in two applications with a target sowing rate of 34 kg/ha separated by 22 days. Application rates achieved on the ground were stratified such that anticipated high risk areas in the cliff s and valleys received additional bait. We consider the following to be key to the success of the second attempt: 1) monitoring environmental conditions prior to the operation, and proceeding only if conditions were conducive to success, 2) reinterpretation of bait availability data using the lower 99% confidence interval to inform application rates and ensure sufficient coverage across the entire island, 3) treating the two applications as independent, 4) increasing the interval between applications, 5) seeking regulatory approval to give the operational team sufficient flexibility to ensure a minimum application rate at every point on the island, and 6) being responsive to operational monitoring and making any necessary adjustments.

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