Certainly, food availability is an important factor acting to limit bird populations ( Newton, 1980), affecting reproductive success and survival of many bird species in different systems ( Martin, 1987). Whether the impacts of supplementary feeding are universal among and within feeder-visiting species remains largely unstudied. 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). 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., 2015, 2017 Orros and Fellowes, 2015a Plummer et al., 2015 Wilcoxen et al., 2015).
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). Effectively a massive ecosystem-scale intervention, bird feeding has numerous potential implications for the biology and ecology of feeder-visiting birds ( Jones, 2011), as well as the wider faunal community (e.g., Bonnington et al., 2014 Orros et al., 2015). In recent decades bird feeding has shifted from a predominantly winter-only activity to a pastime commonly practiced year-round ( Jones and Reynolds, 2008 Horn and Johansen, 2013 Galbraith et al., 2014). Participation rates for engagement in bird feeding are consistently estimated at between one- to two-thirds of households ( Jones and Reynolds, 2008 Galbraith et al., 2014 Orros and Fellowes, 2015b). Garden bird feeding is a phenomenally popular activity in many parts of the world, including in New Zealand, Australia, the UK, Europe, and the USA ( Jones, 2017). Crucially, particularly given the avifaunal context in New Zealand, resource dominance by introduced species could have potential negative outcomes for native species conservation in cities. The observed individual and species-specific differences in supplementary food resource use imply that the impacts of garden bird feeding are not universal. Furthermore, season had an important influence on most visitation parameters. We also found within-species differences in feeder use for all focal species, with individual variation greatest in house sparrows. Significant associations were detected among a number of species, suggesting interspecific interactions are important in determining feeder use. These species were present at feeders most frequently, with the largest conspecific group sizes. Eleven bird species were detected using feeding stations, however, two introduced species (house sparrow Passer domesticus and spotted dove Streptopelia chinensis) dominated visitation events. We used camera traps as well as Radio Frequency Identification (RFID) technology to examine intra- and interspecific feeder visitation patterns and to discern species associations. We investigated patterns of feeder use by garden birds visiting experimental feeding stations in Auckland, New Zealand, with the specific aim of determining whether use of supplementary food was consistent or variable among individuals and species. Individual birds and species that make frequent use of feeders are more likely to experience both the benefits and detrimental impacts of supplementary food. Consistency in feeder use among birds is likely an important determinant of this. However, there is still a paucity of information on the impacts of feeding, including the ubiquity of these impacts among and within feeder-visiting species. Many people engage in the practice of feeding assuming that birds gain some benefit from the food they provide, yet recent studies have revealed the potential for detrimental impacts as well. The practice of garden bird feeding is a global phenomenon, involving millions of people and vast quantities of food annually.
2Centre for Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland, Auckland, New Zealand.1Auckland Museum, Auckland, New Zealand.Beggs 2, Katharina Parry 4 and Margaret C.
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