Data from: Kelp and dolphin gulls cause perineal wounds in South American fur seal pups (Arctocephalus australis) at Guafo Island, Chilean Patagonia

During 5 reproductive seasons, we documented the presence, extent, and origin of perineal wounds in South American fur seal pups (Arctocephalus australis) on Guafo Island, Northern Chilean Patagonia. The seasonal prevalence of perineal wounds ranged from 5 to 9%, and new cases were more common at the end of the breeding season (February), when pups were on average 2 months old and were actively expelling hookworms (Uncinaria sp). Histologically, wounds corresponded to marked ulcerative lymphoplasmacytic and histiocytic dermatitis with granulation tissue and mixed bacterial colonies. In 2015 and 2017, Kelp gulls (Larus dominicanus) and Dolphin gulls (Leucophaeus scoresbii) were observed picking and wounding the perineal area of marked pups. This behavior occurred more frequently after the pups’ defecation, when sea gulls engaged in consumption of pups’ feces. The affected pups usually had moderate to marked hookworm infections along with bloody diarrhea and anemia. Pups with severe wounds (23% of affected animals) had swollen perineal areas and signs of secondary systemic bacterial infection. We propose that seagulls on Guafo Island have learned to consume rests of blood and parasites in the feces of pups affected by hookworm infection, causing perineal wounds during this process. We conclude that this perineal wounding is an unintentional, occasional negative effect of an otherwise commensal gull-fur seal relationship.