Forest-dwelling crab-eating foxes, Cerdocyon thous (Carnivora, Canidae), in eastern Ecuador: new ecological and genetic records of an elusive Neotropical canid.

The crab-eating fox, Cerdocyon thous, is the most broadly distributed native canid in South America, occupying a wide range of ecosystems from open savannas to dense tropical forests from Venezuela to Argentina. Its geographical range is expanding towards the Pacific coast of Central America by crossing the Darien rainforest. In Ecuador, its presence has been poorly documented and remains ecologically ambiguous. In this study, we confirm the presence of C. thous in north-eastern Ecuador based on two roadkill specimens collected in Sucumbíos Province and two independent photographic records from Yasuni National Park, which were obtained through systematic camera-trapping. Stomach-content analysis revealed a predominantly insectivorous and opportunistic diet which includes insects, arachnids, reptiles, and amphibians. In addition, an ectoparasite analysis found parasitism by the introduced cattle tick Rhipicephalus microplus, highlighting potential risks of pathogen transmission between domestic animals and wildlife. Mitochondrial cytochrome b sequences from form a well-supported distinct haplotype from other South American lineages, suggesting that forest-dwelling foxes in eastern Ecuador may represent a separate evolutionary unit with unique ecological adaptations to rainforest environments. These findings underscore the importance of continued monitoring of C. thous in the Amazon, particularly in the context of road expansion, habitat alteration, and increasing interactions with domestic animals such as domestic dogs. Our results have implications for taxonomic assessment, ecological understanding, and conservation planning of this widespread, yet understudied, Neotropical canid in Ecuador.