Migratory Birds: Ecology and Conservation

Migratory Birds: Ecology and Conservation. A report on the BOU’s Annual Conference held at the University of Leicester 5-7 April 2011.

Jenny C. Dunn

RSPB, The Lodge, Potton Road, Sandy, Bedfordshire. SG19 2DL.

In April 2011, the British Ornithologist’s Union’s annual conference took place at the University of Leicester. The theme of this year’s conference was the ecology and conservation of migratory birds, and talks ranged from those focussed on either breeding, migration or wintering ecology, to those linking two or more of these and trying to build a more complete picture of the complex problems faced by long distance migrants. Talks also covered recent technological advances, which are increasingly allowing us intriguing new insights, particularly into the seasonal movements and wintering areas of some of the most declining species. Finally, talks examined the policy challenges associated with protecting migratory species and how best to tackle flyway-scale conservation of migratory birds.

The talks highlighted the progress made in expanding our knowledge of migratory routes and related staging and wintering areas, thanks initially to the contribution of recovery information from ringing studies, and more recently to advances in technology such as geolocators and satellite tags (Baillie et al. 2009). These techniques offer the ability to track individual birds throughout the entire annual cycle, linking ecology on both breeding and wintering grounds (Robinson et al. 2010) and providing crucial information for the design of effective conservation strategies (Martin et al. 2007). However, as always, the amount that is still unknown was also emphasised: much of this knowledge will be critical in aiding our understanding of species’ ecology and thus increasing our ability to effectively conserve migratory birds (e.g. Faaborg et al. 2010a).

The conference began with a welcome address by the BOU President Dr Alistair Dawson and was followed by a keynote speech by Professor Ian Newton OBE FRS FRSE entitled “The ecology of bird migration patterns”. Professor Newton’s talk gave an introduction to the history of research and knowledge of migratory birds, as well as serving to highlight the differences between obligate and facultative migrants. Obligate, or fixed, migrants follow a fixed migration route, with individuals often returning to the same breeding and wintering grounds year after year, a trait thought to be largely under genetic control (Newton 2008). In contrast, facultative, or irruptive migrants tend to migrate when a declining food supply demands it, and show huge variation in both timing of migration and migration route, differing even in the direction of migration from year to year (Newton 2006). Facultative migrants also show very little breeding or winter site fidelity, as revealed by ring recoveries and stable isotope analyses (Marquiss et al. 2008). Finally, Professor Newton suggested that obligate and facultative migrants should be regarded more as a continuum, rather than two distinct entities, citing the case of the White Stork Ciconia ciconia which appears to have both an obligate and a facultative section to its migration strategy (Berthold et al. 2004), continuing to wintering grounds further south if necessary in order to take advantage of food availability.

The first three sessions of the conference focussed on migration ecology, and the first of these opened with a keynote presentation from Dr Peter Marra (Smithsonian Migratory Bird Center, Washington) examining the implications of carry-over effects between seasons, and between breeding and wintering grounds (e.g. Inger et al. 2010). This talk emphasised the importance of taking into account the entire annual cycle of migratory birds when considering any aspect of their ecology, as seasonal interactions may be common (Norris & Marra 2007, Reudink et al. 2009) and in general, research has tended to focus on the breeding season rather than at other stages of the annual cycle (Faaborg et al. 2010b). Satellite tracking technology has greatly increased our ability to track the movements of individuals in some detail for long periods, and the next talk by Dr Kaspar Thorup (Natural History Museum of Denmark, University of Copenhagen, Denmark) summarised data from a satellite tracking study, examining the influence of perpendicular wind on the migration of first year raptors as distinct from adults (Thorup et al. 2003). The raptor theme was continued by Matias Juhant (University of Maribor, Slovenia), who discussed the scarcity of knowledge regarding raptor migration within South America, and emphasised the importance of establishing monitoring programmes using migration counts (Juhant 2010).

Dr Ulf Ottosson (A. P. Leventis Ornithological Research Institute & University of Lund, Sweden) opened the second session, describing a study of Garden Warblers Sylvia borin, trying to piece together the story of this species’ migration through a series of ringing-recapture sites in Africa and providing substantial insight into the over-winter ecology of this species (Ottosson et al. 2005b). The timing of migration has long been known to be under the control of both exogenous and endogenous factors (Styrsky et al. 2004), but how these interact to influence migration timing is less well known. This was the focus of the next talk from Miren Andueza (University of Valencia & Aranzadi Science Society, Spain) who described a study of exogenous and endogenous factors in Sedge Warbler Acrocephalus schoenobaenus migration, emphasising the importance of considering all factors together, rather than each separately, as additive effects may be common. The next talk from Dr Volker Salewski (University of Osnabrück, Germany) discussed the difficulties of differentiating between Eastern Iduna pallida and Western Olivaceous warblers I. opaca (Ottosson et al. 2005a), and of distinguishing resident from migrant populations of both species, highlighting some of the complexities associated with understanding the migration ecology of these two species. The use of stable isotopes has increased dramatically over the past decade, especially in North America (Bowen et al. 2005); however, their use in Afro-Palaearctic migrants is less well developed. Dr Paul Donald (RSPB, UK) spoke about stable isotope work trying to identify the winter distribution of the Aquatic Warbler Acrocephalus paludicola by comparison of stable isotope feather signatures with those of resident African species within the same trophic guild (Flade et al. in press). This talk also highlighted some of the difficulties with this technology, such as the requirement for a detailed knowledge of moulting ecology, pointing out that moulting areas and wintering grounds are not necessarily the same. Consequently, these data need to be accompanied by other complementary approaches, followed by fieldwork to confirm likely wintering locations (Buchanan et al. in press). Dr Elizabeth Yohannes (Max Planck Institute for Ornithology, Germany) continued the stable isotope theme with her talk providing an overview of the use of stable isotopes in avian migration work, and citing an example of hybrid Great Acrocephalus arundinaceus and Clamorous A. stentoreus Reed Warblers with features of both species, where stable isotope analysis enabled the location of hybrid wintering grounds to be established (Yohannes et al. 2011).

The final migration ecology session began with a talk from Dr Rob Robinson (BTO, UK) looking at large scale patterns of demographic responses to climate change in Palaearctic warblers. For example, decreased productivity in woodland species, where temperature change was most rapid, suggested mismatches with the seasonal peak in food availability. Similarly, increased productivity of reed-dwelling species, where temperature change was greatest, suggested that this habitat may be thermally limiting and consequently that survival is responsible for population changes in these species. The second talk in this session was from Dr Fernando Spina (Istituto Nazionale per la Fauna Selvatica, Italy), looking at fat reserves in Barn Swallows in relation to the timing of roosting and migration. Dr Spina illustrated a relationship between fat reserves and the size of habitat barriers, for example, deserts or seas, along migratory routes, revealing that both adult and juvenile birds with larger barriers to cross had larger fat reserves (Rubolini et al. 2002). Teresa Militão (University of Barcelona, Spain) followed this by discussing whether stable isotope analysis can be used to trace migratory routes of Atlantic seabirds and concluded that this method can detect species-specific migratory strategies, but that knowledge of individual species’ moult strategies was crucial in interpreting these data (Ramos et al. 2009). Dr Rob Sheldon (RSPB, UK) closed this session by describing work using satellite tags to establish the migration routes of the Sociable Lapwing Vanellus gregarious, a species for which hunting on migration has been identified as the key threat to the population. Data from satellite tracking has enabled survey and monitoring work to be targeted at key sites along the migratory routes used by this species and hence provide crucial information that will aid the development of appropriate conservation actions.

Dr Jenny Gill (University of East Anglia, UK) opened the next session of talks, aimed at discussing responses to environmental change, with a keynote presentation looking at the population-level responses of migratory birds to environmental change, focussing on the Black-tailed Godwit Limosa limosa. This long-term study investigates the drivers of “seasonal matching” in this species, where breeding and non-breeding ground habitat show marked variation in terms of breeding success and over-winter survival, and a very strong relationship exists between winter and summer habitat quality within individuals (Gunnarsson et al. 2005). Strong seasonal matching is seen only in males, not females and consequently it is thought to be driven by natal site fidelity and may have profound implications in terms of inflating fitness inequalities driven by habitat quality (Gunnarsson et al. 2005). Next, Professor Brian Huntley (University of Durham, UK) described work utilising 20 years of survey data to create models predicting distributional responses to climate change in migrant species. These models predicted shifts in both breeding and non-breeding ranges resulting in a predicted 25% increase in migratory distance (Doswald et al. 2009), although a change in migratory strategy was proposed as an alternative possibility, whereby sub-Saharan migrants could potentially winter north of the Sahara as habitat becomes suitable. Alternatively, birds may respond to an increased availability of habitat suitable for breeding and wintering and consequently become resident in part of their range. Adam Seward (University of Cardiff, UK) followed this by presenting results from supplementary feeding experiments in breeding Northern Wheatears Oenanthe oenanthe, where pairs provided with supplementary food were more likely to have an extra breeding attempt, and recruit offspring into the breeding population.

The second day opened with a second session discussing responses to environmental change and began with a talk by Dr Silke Bauer (Swiss Ornithological Institute, Switzerland) looking at how environmental change might affect the departure cues used by birds in timing their migration. This talk emphasised how little we know about the external cues affecting departure dates of migrants and the need to develop a greater understanding of these cues before we can predict the consequences of environmental change for migrant species. Catriona Morrison (University of East Anglia, UK) continued this session by discussing contrasting population trends between Willow Warblers Phylloscopus trochilus in Scotland and the south east of England (Morrison et al. 2010), with nest-specific rainfall data showing high failure rates in warm and dry conditions. Urbanisation causes changes in microclimate that may impact upon bird behaviour through higher temperatures and greater food availability (Partecke & Gwinner 2007), and Mikkel Kristensen (Copenhagen Natural History Museum, Denmark) discussed the possibility of distinct migration behaviour between urban and rural birds. Urban populations did appear to have adapted to these changes, with both blackbirds and great tits reducing their migration distance compared to their rural counterparts, and urban blackbirds showing a decrease in the number of migrating individuals, suggesting a higher degree of residency. Next, Dr Juliet Vickery (RSPB, UK) discussed early results of a large-scale project in Ghana and Burkina Faso monitoring migrants across a range of habitat types and highlighted the importance of using multiple conservation tools, considering socio-economic impact of conservation actions, and taking a co-ordinated flyway approach when dealing with migratory species. This session was concluded by a Techspot from Vicky Jones (Birdlife International) introducing the Critical Site Network Tool, a tool for conservation planning and management of waterbirds accessible at

The next session focussed on the practicalities of putting science into practice in terms of management for migratory birds, and began with a talk from Dr José Alves (University of East Anglia, UK) looking at the energetic costs of geographic variation in Black-Tailed Godwit wintering grounds, and showing that the costs of migrating longer distances and over-wintering further south are outweighed by lower energetic living costs and reflected in an earlier arrival date on breeding grounds and an increased reproductive success. Dr Nigel Clark (Delaware Shorebird Project & BTO, UK) followed this by describing the difficulties involved in establishing compromise between interested parties where overfishing of Horseshoe Crabs Limulus polyphemus at the final stopover site for Red Knot Calidris canutus in Delaware Bay has led to a catastrophic decline of this species (Haramis et al. 2007). Whilst no long-term management solution has yet been established, a major hurdle has been overcome as fishery groups now appreciate that management of Horseshoe Crab fishing is essential for the recovery of Red Knot populations. Conference talks then moved on to the implementation of conservation through policy, focussing first on the construction of Species Action Plans (SAPs), with Tim Jones (DJEnvironmental, UK) discussing the problems faced when constructing and implementing action plans for migratory species, emphasising the need for international supported and cooperation and a mutual shared will over a large geographic scale. Dr Norbert Schäffer (RSPB, UK) described one example of a successfully implemented action plan, the EU SAP for the Corncrake Crex crex, which was largely driven by changing mowing practices in the breeding areas to enhance nestling survival (Schäffer & Weisser 1996). Many lessons learned from the Corncrake SAP have been incorporated during the development of the SAP for the Aquatic Warbler: SAPs are more likely to be successful when a species faces similar problems across its whole range, and when the SAP is ‘owned’ by an individual or institution, and driven by the chairman of the working group. Dr Tim Stowe (RSPB, UK) concluded this session by examining practical approaches to implementing conservation strategies for African-Eurasian migrants, emphasising that whilst an international agreement is a very important start it needs to be complemented by action on the ground at regional and national levels. The identification of key wintering and stopover sites are particularly important for waders and soaring birds; however, there are still many unanswered questions regarding the migration of passerines which migrate on a broad front, and conservation resources need to be focussed on identifying key habitats and locations in the sub-Saharan region in order to gain a greater understanding of factors influencing population declines of these species.

Professor Franz Bairlein (Institute of Avian Research, Germany) opened the final session, discussing future knowledge and policy needs, with a key-note presentation discussing current knowledge and future perspectives for the effective conservation of migratory birds. Professor Bairlein’s talk emphasised the importance of stopover sites and concluded by stressing the importance of integrating theory with reality and identifying the mechanisms driving population trends for each species. Declining population trends are generally associated with a lack of adaptation to changing conditions; however, Professor Hanna Kokko (Australian National University, Australia) pointed out that interpretation of population trends resulting from environmental change can be tricky, citing a model of partial migration in Finnish Skylarks Alauda arvensis where a higher proportion of the population remaining resident as a result of climate change could potentially lead to population declines as a result of increased adaptation. The final talk of the conference was from Dr Ian Bainbridge (Scottish Natural Heritage, UK), examining future projections for the requirements of migratory birds. Future conservation strategies need to take into account both daily and annual cycles; however, policy tends to be less effective across annual cycles and site-based conservation measures work better for some species than others, highlighting the need for flexibility. Site-based conservation is particularly difficult when species are mobile over-winter and frequently a lack of knowledge as to the location of wintering grounds hampers conservation efforts. Human population growth, with it’s associated habitat destruction and degradation is likely to be one of the biggest problems restricting conservation effort for migratory birds.

Dr Danaë Sheehan rounded off the conference with a summary, reviewing the approaches, challenges, and priorities for future research highlighted throughout the conference. Many challenges were suggested: one of the main priorities should be seen as getting these issues onto the agendas of multilateral agreements and making them effective. Research priorities tended to focus on factors on wintering grounds – such as identifying key drivers of population trends, investigating socioeconomic drivers, habitat choice, and factors driving variation in seasonal survival and regional variation in population trends. Investigating factors driving declines in migratory seabirds, managing water and wetlands for migrants in a changing climate, and establishing the effects of climate change on productivity and migration strategies were also among those issues highlighted as research and conservation priorities.