Wild bird feeding (probably) affects avian urban ecology

Abstract

Why do people feed wild birds? It is intuitively clear that humans feel delighted by the presence of birds that they can manage to attract by offering ordinary seeds at a feeder. According to surveys on human motivations for feeding wild birds in Australia, some people may gain experiential knowledge from observing the birds in their gardens, or feed the birds in return for the massive habitat destruction caused by humans ( Howard & Jones, 2004 ; Ishigame & Baxter, 2007 ). However, outside Australia, the largely unstudied motivations of people feeding birds are just one example for our gaps of knowledge with respect to bird feeding ( Jones & Reynolds, 2008 ). It is in sharp contrast to our limited knowledge on the habit that wild bird feeding is probably the most widespread and popular form of human–wildlife interaction throughout the world ( Jones, 2011 ), and, at least in northern temperate regions, the largest wildlife management activity ( Martinson & Flaspohler, 2003 ). In the UK, suffi cient commercial wild bird foods are sold to support a hypothetical number of over 30 million great tits ( Parus major ; Robb et al., 2008a ), which is many more than the 2 million pairs of great tits that are actually present (www.bto.org). Surveys have found that 64% of households provide supplementary food for birds in the UK ( Davies et al., 2012 ), and 43% in the USA ( Martinson & Flaspohler, 2003 ). In suburban and rural environments of Australia, estimated household feeding rates range from 36% to 48% ( Ishigame & Baxter, 2007 ). Although BirdLife Australia does not encourage supplementary feeding of wild birds ( Bird Observation and Conservation Australia, 2010 ), northern organizations such as the British Trust for Ornithology (BTO), the Royal Society for the Protection of Birds (RSPB) and the Cornell Laboratory of Ornithology now recommend feeding birds for promoting nature conservation ( Jones, 2011 ). In Germany, a renowned ornithologist recently wrote a popular book on bird feeding that sold 50,000 copies in the fi rst 1.5 years, in which he advocates feeding the birds year-round and on a massive scale ( Berthold & Mohr, 2008 ). Indeed, wild bird feeding is not only here to stay ( Jones, 2011 ), it also seems to be increasing, at least in the UK ( Chamberlain et al., 2005 ). Today, in many countries, the huge effort in providing supplementary food for birds may be one of the largest human infl uences on bird populations, in addition to habitat loss and change, humaninduced climate change and hunting. As I will show in this chapter, we now have a sound basis of knowledge about the impacts that supplementary feeding can have on birds. However, as I will also show, our knowledge mostly comes from smallscale experiments that researchers did in natural and rural habitats. Surprisingly little is known on the impact of feeding birds in our urban gardens and backyards. However, humans are infl uencing urban food supply for birds not only directly by providing feeders, but also via waste treatment and by creating, changing, or destroying urban or natural habitats and food sources in our cities ( Chace & Walsh, 2006 ). Because such additional human infl uences are usually weaker in rural landscapes, the effects of feeding wild birds are likely