Invited article: The impacts of non-native species: a review of the British Ornithologists’ Union's Autumn 2008 Scientific Meeting: The impacts of non-native species

The 1995 conference on naturalized and introduced birds organized by the British Ornithologists’ Union (BOU) and the Joint Nature Conservation Committee (JNCC) (Holmes & Simons 1996a) provided a benchmark in the understanding of the status and impacts of such species in the United Kingdom. That conference stemmed from a growing realization of the numbers and diversity of bird species that had become established in the UK as a result of introduction by humans and led to important changes in the way that the status of such species is assessed (Holmes & Stroud 1995, Holmes et al. 1998). Existing legislation was reviewed (Holmes & Simons 1996b) and conference presentations highlighted a range of conservation problems, as well as existing plans for control programmes (e.g. Hughes 1996). Since then much has been learnt, in terms of both the status of individual species and their ecological and economic impacts (see review by Manchester & Bullock 2000), and policy in this area has been developed to reflect this. The BOU’s Autumn 2008 Scientific Meeting on ‘The impacts of non-native species’, held in Peterborough, UK, aimed to provide an overview of the present state of knowledge and action on this issue. Here we provide a review of the conference; papers from the conference can be accessed via the BOU ProcNet website (http://www.bouproc.net/). The scope of the 2008 conference differed from that in 1995 in that the impacts of other non-native taxa on native bird species were also considered. Although focusing on the UK, the 2008 conference also encompassed the UK Overseas Territories (UKOTs), an important and developing area of concern. Due to the breadth of this scope, some subject areas considered in 1995 were not included, notably the impacts of naturalized introduced gamebirds (see Balmer et al. 1996, Robertson 1996). Nevertheless, this is an area where there has been an increasing amount of research in recent years, in terms of both the possible benefits of associated habitat management for native bird species (Draycott et al. 2008) and potential adverse impacts on native species, including the spread of disease from reared and released birds (Tompkins et al. 2000). Non-native species may have a range of negative impacts on indigenous species, including competition, predation, disease and genetic effects (i.e. hybridization) as well as impacts on ecosystem function through habitat alteration (Manchester & Bullock 2000, Lever 2005, Sol et al. 2005). Furthermore, non-native species may impact on human interests, for example by causing health risks and economic losses, in agriculture, forestry, aquaculture and other sectors (Pimentel et al. 2005). Sol et al. (2005) highlighted five priorities required to deal with the problems that non-natives pose: research, monitoring, legislation, mitigation and informing the public. These themes were much in evidence throughout the 2008 conference and in many of the individual papers. The first aim of the 2008 conference was to present a series of case studies, ranging from studies of well-established non-natives to those newly established or less well studied. In his paper for the 1995 conference, Hughes (1996) reviewed the threat that Ruddy Ducks Oxyura jamaicensis, introduced in the Western Palearctic, posed to the native White-headed Duck Oxyura leucocephala through hybridization and competition, and early plans for implementing control measures. Following these initial control trials (Hughes et al. 2006), and further large-scale research (Hughes et al. 1999, Smith et al. 2005), a 5-year control programme was started in 2005 with funding from EU LIFE-Nature and the UK’s Department for Environment, Food and Rural Affairs (Defra). This integrated programme of research and action is the most complete to date for a non-native bird species in the UK. Its success and the present status of the Ruddy Duck in the UK were reviewed for the conference by Henderson (2010). The development of our understanding of non-native species and of associated UK policy since the 1995 conference is apparent in that recent risk assessments (commissioned by the Great Britain Non-native Species Secretariat) formed the basis of talks on the status and potential impacts of parakeets and Eurasian Eagle Owls Bubo bubo. The potential impacts of introduced Rose-ringed Parakeets Psittacula krameri in the UK as an agricultural pest and as a competitor with native species for nest-sites were previously recognized by Feare (1996) and since then the UK population has expanded greatly in numbers, if not yet in range (Butler 2002, Fletcher & Askew 2007). Tayleur (in press) reviewed the present status of the species in the UK and evidence for impacts to date, as well as the recent establishment of a small population of Monk Parakeets Myiopsitta monachus. The establishment of the Eurasian Eagle Owl in the UK has been more recent, with the first documented breeding in 1984 and annual breeding since 1997. The status of this species in Britain was recently reviewed by Melling et al. (2008), who concluded that all UK records probably involved birds of captive origin, rather than wild native birds colonizing from continental populations. Toms (2009, 2010) reported on the likelihood of the species becoming more widely established and identified possible impacts on a range of native species, including Pine Marten Martes martes, Capercaillie Tetrao urogallus and Long-eared Owl Asio otus. Non-native geese have been established for much longer in the UK and the continuing population growth of two species, the Greater Canada Goose Branta canadensis and Egyptian Goose Alopochen aegyptiacus, was reviewed for the conference by Rehfisch et al. (in press). There is often a lack of clear evidence as to the actual impacts of non-native species, and as this work highlighted, this problem is not restricted to less common or recently established species. The status and potential impacts of non-native waterbirds in countries within the African-Eurasian Waterbird Agreement (AEWA) area were summarized by Wright et al. (in press). Based on a recent review (Banks et al. 2008, itself updating an earlier review: Blair et al. 2000, Rehfisch et al. 2006), this work further highlighted the need for increased research and quantification of the impacts of non-native waterbirds and for improved national legislation, but also that many countries currently lack effective monitoring and the measures or resources to prevent introductions of non-native waterbirds. Even in countries with legislation in place to prevent the introduction of non-native species, introductions still occur (Shaw 2006). The impacts of introduced mammals on island bird populations have long been recognized (Atkinson 1989, Blackburn et al. 2004). Recently in the UK, there has been particular concern over the impacts of introduced Hedgehogs Erinaceus europaeus and American Mink Neovison vison on breeding wader and seabird populations in the Outer Hebrides and other Scottish islands (Craik 1995, 1997, Jackson & Green 2000, Jackson et al. 2004, Ratcliffe et al. 2005). Control programmes have been set up to eradicate these predators (Jackson 2001, 2005, Scottish Natural Heritage 2004, Hebridean Mink Project 2006). Luxmoore et al. (2010) reviewed a similar programme that has successfully eradicated introduced Brown Rats Rattus norvegicus from the island of Canna, thereby allowing the re-establishment of a formerly large colony of Manx Shearwaters Puffinus puffinus. Non-native species – in particular mammals – are a significant problem in the UKOTs (Varnham 2006), which are nearly all remote islands and which consequently support many endemic and restricted-range bird species, as well as some of the world’s most important seabird colonies. Hilton and Cuthbert (2010) reported that mammalian predators have caused enormous reductions in seabird mega-colonies in the UKOTs (for example on Ascension, St Helena and Tristan da Cunha), likely to be in the order of many millions of breeding pairs, as well as losses of endemic land-birds. Recent progress on the eradication of these predators and plans for future schemes were also reviewed. Introduced mammals have impacted native bird populations not only through predation, but also through alteration of habitats. In Great Britain, there has been concern as to the impacts of the ongoing large increases in abundance and distribution of deer on woodland biodiversity (Fuller & Gill 2001), and the particular impacts of introduced Reeves’ Muntjac Muntiacus reevesi and Fallow Deer Dama dama were reviewed by Fuller and Gill (2010). Deer activity notably reduces the vegetation structures that provide nest-sites, feeding sites and shelter for bird species dependent on woodland understories; other impacts may include increased predation risk, trampling and alteration of food supplies (Fuller 2001). The impacts of non-native deer species may not solely be additive to those of native species, as there is probably sufficient inter-specific variation in the ecology and behaviour of these species to result in differential impacts on vegetation structure and composition. Sol et al. (2005) provided a useful summary of the processes of establishment of non-native populations, and helpful clarification of terminology. In their review, an introduced species is one that has been transported outside of its native range and which is released or escapes into a new environment; an established or naturalized species is one that forms a self-sustaining wild population following introduction; and an established or naturalized species that succeeds in spreading beyond the site of introduction is termed an invasive. The 1995 BOU/JNCC conference had earlier highlighted the problems presented by the variety of terms used to describe non-native bird species (Holmes & Simons 1996a) and this led to a review of the terminology used to describe their status in Great Britain (Holmes & Stroud 1995). In turn, this resulted in a major review of the categorization of bird species on the British List, overseen by the BOU’s Records Committee (BOURC) (Holmes et al. 1998). The approach of linking terminology to process is followed by the BOURC, whereby Category C comprises ‘species that, although introduced, now derive from the resulting self-sustaining populations’ and Category E comprises ‘species that have been recorded as introductions, human-assisted transportees or escapees from captivity, and whose breeding populations (if any) are thought not to be self-sustaining’ (BOU 2006). Dudley (2010) presented a summary of the most recent review of the status of introduced, naturalized bird species in Britain (Dudley 2005) and highlighted those non-native species which are potential admissions to the British List. These, notably, include the Sacred Ibis Threskiornis aethiopicus, the emblem of the BOU, which is now firmly established in France and has impacted native waterbird species through nest predation and nest-site competition (Kayser et al. 2005, Yésou & Clergeau 2005). The need for improved monitoring of non-native bird species was highlighted at the 1995 conference (Marchant 1996) and following the recommendations made then there has been a significant improvement in the scope of surveillance for these species at a UK level, as well as in other European countries. Records of all but the most common non-native bird species breeding in the UK are now summarized in an annual report (Holling and the Rare Breeding Birds Panel 2007). There are also currently plans to establish a non-native species surveillance scheme in Great Britain, and a government non-native species indicator. Stroud (in press a) reviewed past and current treatment of non-native bird species by the main ornithological schemes in the UK, and the main international legislation driving this. Whilst some international treaties such as AEWA have periodically reviewed the status of groups of non-natives at an international scale (as reported by Wright et al. in press), information on non-native birds at continental scales is lacking, and there clearly remains a need for greater monitoring effort to inform national risk assessments and management plans. The development of our understanding of the problems that non-native species can cause and the resultant need for co-ordinated action led to the launch, in 2008, of Defra’s Invasive Non-Native Species Framework Strategy for Great Britain (Defra 2008). This strategy adopts the three-stage hierarchical approach set out in the Convention on Biological Diversity 1992 of implementing prevention measures, followed by early detection and rapid eradication and, subsequently, longer term containment and control/management as necessary. This approach thus incorporates a number of priorities (also highlighted by Sol et al. 2005, see above): prevention; early detection, surveillance, monitoring and rapid response; mitigation, control and eradication; as well as important cross-cutting issues such as building awareness and understanding; legislation; research; information exchange and integration (Thomas 2010). Prevention provides the most cost-effective approach to minimize the risks posed by non-natives, and is the focus of much of the relevant legislation. Wilson and Heydon (in press) provided an overview of current legislation as pertaining to England. Obligations to regulate or prohibit the introduction of non-native species are set out in international conventions and directives, such as the Convention on Biological Diversity (CBD), the Bern Convention, the European Union (EU) Birds Directive (2009/147/EC) and the EU Habitats Directive (92/43/EEC). The primary piece of British legislation aiming to protect native biodiversity from the impacts of non-native species through their release or escape into the wild (and to implement the provisions of the EU Birds and Habitats Directives) remains the Wildlife & Countryside Act 1981 (as amended). Wilson and Heydon (in press) highlight weaknesses in this legislation, for example in the use of problematic or inconsistent definitions, and the different approaches taken to control or limit the impacts of non-native species at different stages of establishment (established and widespread species, established but localized Species and potential colonizers). Conclusions from the conference are outlined by Stroud (in press b) and broadly follow the priorities of the Invasive Non-native Species Framework Strategy referred to above. A number of key points were highlighted by speakers during the conference and in these conclusions. Walton (2010), for example, highlighted three outstanding imperatives – to ensure that developing policies retain sound biological rationales, that action is implemented urgently and that legislative frameworks are adequate to support policies. There is clearly also scope to improve the information flow from research and monitoring programmes to action plans, and a need for improved communication, education and public awareness (Bremner & Park 2007). Not least, it is clear that resourcing will be fundamental to the success of the strategy. The UK is one of relatively few EU member states to put in place a national strategy, and is engaging with the issue at an international level to promote progress. In December 2008, the European Community (EC) adopted a Communication presenting policy options for an EU Strategy on Invasive Species (proposed in the European Commission’s Action Plan for the EU 2010 Biodiversity Target). EC policy is centred on the same CBD approach adopted in the Invasive Non-Native Species Framework Strategy for Great Britain and will provide an opportunity to develop EU legislation, bringing all member states up to a shared, co-ordinated legislative standard. Despite this progress, there remains much to do, notably beyond the EU. Stattersfield and Capper (2000) indicate that invasive species have played a role in the majority of all bird extinctions since 1800, particularly island species lacking natural defences to introduced predators. It is of extreme concern, for example, that 298 species (25%) of globally threatened birds are currently affected by introduced mammals. A recent review has also identified invasive species as one of the main threats to the world’s Critically Endangered birds (BirdLife International 2008). It is thus particularly important that a similar strategy on non-natives is urgently developed to protect the globally significant biodiversity of the UKOTs. Within Britain, the priority must now be to translate the Invasive Non-Native Species Framework Strategy into effective action on the ground. This remains perhaps the most difficult challenge in the process of dealing with non-native species but, ultimately, the only true measure of its success. On behalf of the BOU, we would like to thank the following organizations for sponsoring the conference and the proceedings from the conference: the British Trust for Ornithology, Defra, Joint Nature Conservation Committee and Natural England. Our thanks also to all the authors who presented papers at the conference: Iain Henderson, John Tayleur, Richard Luxmoore, Rob Fuller, Mark Rehfisch, Lucy Wright, Mike Toms, Steve Dudley, David Stroud, Charles Wilson, Paul Walton and Huw Thomas, and to David Stroud and Colin Galbraith for leading the discussion, as well as those who reviewed the papers for these proceedings. We are grateful to BOU’s Steve Dudley and Angela Langford for running the conference itself and their work with the proceedings. We hope that, as with the 1995 conference, these proceedings will provide an impetus for further research and monitoring on non-native species and further integrate this work with legislation and policy.