The underestimated role of carrion in vertebrates' diet studies

Aim: Despite the increasing scientific evidence on the importance of carrion in the ecology and evolution of many vertebrates, scavenging is still barely considered in diet studies. Here, we draw attention to how scientific literature has underestimated the role of vertebrates as scavengers, identifying the ecological traits that characterize those species whose role as scavengers could have gone especially unnoticed. Location: Global. Time Period: 1938–2022. Major Taxa Studied: Terrestrial vertebrate scavengers. Methods: We analysed and compared (a) the largest database available on scavenging patterns by carrion-consuming vertebrates, (b) 908 diet studies about 156 scavenger species and (c) one of the most complete databases on bird and mammal diets (Elton Traits database). For each of these 156 species, we calculated their scavenging degree (i.e. proportion of carcases where the species is detected consuming carrion) as a proxy for carrion consumption, and related their ecological traits with the probability of being identified as scavengers in diet studies and in the Elton Traits database. Results: More than half of the species identified as scavengers at monitored carcasses were not assigned carrion as food source in their diet studies nor in the Elton Traits database. Using a subset of study sites, we found a direct relationship between a species' scavenging degree and its rate of carrion biomass removal. In addition, scavenger species, which were classified as non-predators and mammals had a lower probability of being identified as scavengers in diet studies and in the Elton Traits database, respectively. Main Conclusions: Our results clearly indicate an underestimation of the role of scavenging in vertebrate food webs. Given that detritus recycling is fundamental to ecosystem functioning, we encourage further recognition and investigation of the role of carrion as a food resource for vertebrates, especially for non-predator species and mammals with higher scavenging degree.

JM was supported by a Basque Government predoctoral grant (PRE_2018_2_0112), ZMR, LNA and EA by contracts co-funded by the Generalitat Valenciana and the European Social Fund (ESF) (APOSTD/2019/016, ACIF/2019/056 and APOSTD/2021/028 respectively). MM, JMPG and ESG were funded by MCIN/AEI/10.13039/501100011033, by ‘European Union NextGenerationEU/PRTR’, ERDF ‘A way of making Europe’ and by ESF ‘Investing in your future’ (grant numbers RYC-2015-19231, IJC-2019-038968, TED2021-130890B-C21, PID2021-128952NB-I00 and RYC-2019-027216-I). ESG was also partially funded by the HORIZONMSCA-2021-SE-0 action number: 101086387, ‘REMARKABLE’ project. ZMR and DRG were also funded by the Junta de Andalucía (POSTDOC_21_00353 and PREDOC_00262). RPR was co-funded by the ESF and Plan Propio I+D+i UCLM.