Flying the extra mile pays-off: foraging on anthropogenic waste as a time and energy-saving strategy in a generalist bird

Abstract

Food waste disposal represents a major global source of predictable anthropogenic food subsidies and is exploited by many organisms. However, the energetic cost-benefits of foraging on these food subsidies have remained largely unexplored. Here we investigate the year-round foraging decisions of resident white storks, Ciconia ciconia, in Iberia and assess the energetic and time cost-benefits of foraging on both landfill waste and natural food sources. To do so, we use GPS and acceleration data from 55 individuals tagged in southern Portugal between 2016 and 2019. We find that the probability of attending landfill sites was 60% during the non-breeding season and 44% during the breeding season. Moreover, foraging on landfill waste is a time- and energy-saving strategy; although birds had to travel 20% further to exploit this resource during the breeding period, they spent overall 10% less energy than when foraging on natural prey. We show that this relationship could be mediated by a reduction in foraging time and an increase in foraging efficiency while exploiting landfill waste. Surprisingly, we did not find any evidence that landfill specialists experienced any competitive advantage during landfill exploitation over birds that visit landfills occasionally. These insights are key to predict how species that rely on landfills can be affected by waste reduction initiatives planned by the European Union, and implement the necessary management strategies.