White-faced and Black-faced ibises foraging on predictable anthropogenic food subsidies in Patagonia, Argentina

Waste associated with human activities can benefit opportunistic species at the individual and population levels but could also expose them to pathogens or toxins. We provide information on unreported foraging habits of White-faced ibis (Plegadis chihi) and Black-faced ibis (Theristicus melanopis) in the Chubut River Valley, an urban and agricultural landscape in eastern Patagonia, Argentina. Both species were recorded during monthly counts made between February and June 2021 at anthropogenic food sources along the lower river valley, although almost exclusively at those sites offering waste from livestock production. This is the first record of both species foraging at this type of food source of human origin. White-faced and Black-faced ibises were present in numbers that varied between 2 and 679 individuals and between 1 and 18 individuals, respectively, depending on the site and month. Both species were recorded walking over carcasses and viscera and probing into these remains or on the soft soil surrounding the ponds where liquids generated by rendering processes were disposed. Given the current growth in livestock production in the area, further monitoring and assessment at other months of the year are needed to adequately interpret the species trophic ecology and the potential conflicts with human populations.