Mitigating GHG emissions: A global ecosystem service provided by obligate scavenging birds

Abstract

Dead animals release greenhouse gases to the atmosphere through natural decomposition or because they have to be processed by disposal methods such as composting or rendering. Obligate scavenging birds (vultures) consume dead animals and are among the most efficient terrestrial scavengers. They may therefore contribute to a considerable reduction in sources of greenhouse gases. Here, we quantify the global contribution of vultures in reducing greenhouse gas emissions by consuming organic material. First, we evaluated a scenario where all the dead animals that can be consumed by vultures every year have to be disposed of by composting, anaerobic decomposition (e.g., burial), anaerobic digestion or rendering. Second, we assessed a scenario in which dead animals are left to decompose in the environment. Current vulture populations (∼134–140 million individuals) may reduce emissions of 3.03–60.70 Tg CO2 eq. per year, depending on the disposal method implemented, without considering carcass transport to disposal plants. Alternatively, they may reduce emissions of 13.02 Tg CO2 per year if dead animals remain in the environment. Over recent years a decline in vulture populations worldwide has led to a decrease of a 30 % in their capacity to mitigate greenhouse gases emissions. A few abundant vulture species reduce almost 98 % of the maximum emissions potentially removed worldwide by all extant vulture species over one year. This ecosystem service contributed by vultures to humans and nature cannot easily be replaced by other species, including humans. Moreover, supplanting this contribution with alternative carcass disposal methods is expensive and harmful to the environment due to emissions generated in the process. Our results highlight an important service that vultures provide worldwide, which is relevant in the current context of global warming.