Is supplementary feeding in gardens a driver of evolutionary change in a migratory bird species?

Abstract

Human activities are causing rapid environmental change at a global scale. Urbanization is responsible for some of the most extreme human-altered habitats and is a known driver of evolutionary change, but evidence and understanding of these processes is limited. Here, we investigate the potential underlying mechanisms contributing to the contemporary evolution of migration behaviour in the Eurasian blackcap (Sylvia atricapilla). Blackcaps from central Europe have been wintering in urban areas of Britain with increasing frequency over the past 60 years, rather than migrating south to the Mediterranean. It has been hypothesized that the popularization of providing supplementary foods for wild birds within Britain may have influenced this marked migratory change, but quantifying the selective forces shaping evolutionary changes remains challenging. Using a long-term national scale data set, we examine both the spatial distribution and interannual variation in blackcap wintering behaviour in Britain in relation to supplementary food availability and local climate. Over a 12-year period, we show that blackcaps are becoming increasingly associated with the provision of supplementary foods in British gardens, and that the reliability of bird food supplies is influencing their winter distribution at a national scale. In addition, local climatic temperatures and broader scale weather variation are also important determinants of blackcap wintering patterns once they arrive in Britain. Based on our findings, we conclude that a synergistic effect of increased availability of feeding resources, in the form of garden bird food, coupled with climatic amelioration, has enabled a successful new wintering population to become established in Britain. As global biodiversity is threatened by human-induced environmental change, this study presents new and timely evidence of the role human activities can play in shaping evolutionary trajectories.

Garden Bird Feeding: Insights and Prospects from a North-South Comparison of This Global Urban Phenomenon

“…In contrast, changes in migration patterns of some species such as the Eurasian blackcap have led to more enduring changes to community structure because birds are now present throughout the winter in the UK. This is a trend that has grown in blackcaps in the last 60 years and appears to be closely related to the increased availability of feeders in gardens (Plummer et al, 2015). We expect that urban bird communities will continue to be sensitive to anthropogenic feeding practices resulting in foods being available year-round.…”

“…However, even among the well-studied examples such as Eurasian blackcaps Sylvia atricapilla (Plummer et al, 2015) and white storks Ciconia ciconia (Massemin-Challet et al, 2006), it is difficult to disentangle various other potential influences such as the effects of climate change.…”

The breeding performance of raptors in urban landscapes: a review and meta-analysis

“…In fact, the density of birds, in particular some passerine species and Feral Pigeons (Columba livia), is thought to increase with urban cover due to the association with higher food abundance (Blair 1996;Marzluff 2001;Tratalos et al 2007). Furthermore, the migratory behaviours of some species may be altered due to the increased consistency and abundance of food (Plummer et al 2015). Urban environments may also present some species with increased nesting habitat, including natural vegetation and artificial nest boxes (Harper et al 2005;Jokimäki et al 2016Jokimäki et al , 2017.…”

Urban Bird Feeders Dominated by a Few Species and Individuals

“…Although studies of bird-feeding impacts in urban habitats are rare, there is mounting evidence to confirm that garden bird feeding can be profoundly influential for urban-dwelling bird communities (Amrhein, 2014). For example, feeding can alter body condition, reproductive outputs, adult survival, disease dynamics, community assemblages, and migration (Robb et al, 2008;Jokimäki and Kaisanlahti-Jokimäki, 2012;Galbraith et al, 2015Galbraith et al, , 2017Orros and Fellowes, 2015a;Plummer et al, 2015;Wilcoxen et al, 2015). The vast body of scientific literature on the influence of supplementary feeding on a wide range of species and non-urban habitats corroborates many of these findings (e.g., Boutin, 1990;Clout et al, 2002;Ilarri et al, 2008;Schoech, 2009;Ruffino et al, 2014).…”