Seeing the bigger picture: how anthropogenic landscape modification in Africa affects declining migratory birds and the need for trans‐continental research and conservation

Population trends of European birds are becoming increasingly well monitored and are used to identify ecologically related suites of species that show consistent patterns of decline. This synthetic process has identified several major patterns that reflect systematic declines in biodiversity in certain functional groups of species (PECBMS 2012) and this has driven European-based conservation action in recent decades. As an example, the issue of how the continuing, long-term decline of Europe’s farmland bird populations may be reversed has been rarely out of the spotlight of applied ecologists for some decades (Newton 2004a, Donald et al. 2006, Verhulst et al. 2007, Butler et al. 2010, Baker et al. 2012). Until recently, however, little attention had been paid to understanding factors that operate outside Europe, for those species that occupy geographically distant landscapes for almost two-thirds of their life cycle. When viewed as a suite of species in their own right, populations of long-distance migrants are also systematically showing rapid and worrying declines, often in contrast to resident species and short-distance migrants (Berthold et al. 1998, Sanderson et al. 2006, Heldbjerg & Fox 2008, van Turnhout et al. 2010), for reasons that are generally poorly understood. In our efforts to determine and address those population-limiting factors operating on our doorstep in Europe, have we lost sight of the bigger picture of relevance to migratory birds? European-based research aiming to identify factors associated with the population declines of birds in Europe has, in the most part, identified no single proximate cause (Newton 2004a,b). Different species respond to different environmental changes, and population declines are often associated with multiple factors operating simultaneously (Green 2002). However, in many cases, anthropogenic habitat degradation appears to play a major role (Newton 2004a,b). This has been particularly true in the case of birds of European farmland, with resounding supporting evidence suggesting that declines have been primarily driven by a wide range of environmental consequences of the intensification of arable and pastoral farming systems (Newton 2004a, Donald et al. 2006). In contrast to resident species, migratory bird populations may be affected by threats on the breeding grounds, on the wintering grounds and at stopover sites in between, making them vulnerable to the effects of environmental change at a particularly wide geographical scale (Newton 2004b). Potential drivers of population declines in long-distance migrants are diverse and are spread across the migratory cycle – anthropogenic landscape modification is widespread throughout the Africa–Eurasia flyway, both historically and recently (Zwarts et al. 2009). In the last few decades it has been exacerbated by the increasing rate of human population growth, particularly in African nations (Turner et al. 1993, Cleaver & Schreiber 1994), coupled with the more insidious effects of climate change (Gregory et al. 2005, Thornton et al. 2006, Boko et al. 2007, FAO 2007). It is now likely that there are few truly pristine, unaltered habitats left within the range states of migratory species, with most landscapes showing some degree of modification as a result of anthropogenic competition for natural resources in an increasingly human-dominated world. Anthropogenic modification of landscapes may be subtle (e.g. selective felling of individual trees) or dramatic (e.g. slash and burn agriculture). Whilst recent arboricultural practices will have undoubtedly altered once-pristine forested and wooded landscapes, it is the transformation of agricultural landscapes, driven by intensification of arable or pastoral farming systems and generally occurring on a wider geographical scale, that is more obvious. In these systems, change has been particularly rapid in recent decades, driven by the relentless search for food security for rapidly increasing human populations. The associated landscape changes that took place in Europe in the early to middle part of the 20th century have, in the last three decades, started to be mirrored in Africa (McCann 1999, Robinson & Sutherland 2002, Pretty et al. 2011). Taking note of the rapid and alarming population declines of long-distance migrants, researchers have recently started to focus more attention on Africa in an attempt to assess whether the main drivers of their decline lie on the European breeding grounds or on the staging or wintering grounds in Africa. Recognizing the *Corresponding author. Email: danae.sheehan@rspb.org. uk