Storm-Petrels Aggregate on the Open Sea to Feast on Opportune Blubber

Scavenging by seabirds at marine mammal carcasses on the open sea is a poorly documented phenomenon, especially among the smaller species of procellariiformes. During a pelagic survey in the Galápagos, I recorded at least fifty Elliot's storm-petrels (Oceanites gracilis) foraging at a large piece of drifting blubber. Individuals pattered at the sea surface to pick up oil droplets, a foraging mode consistent with storm-petrel ecology yet rarely documented in the context of mammal carcasses. Reports in other species emphasize consumption of blubber or tissue, but this observation suggests that small-bodied seabirds may instead exploit the more metabolically efficient liquid fraction. This observation raises questions regarding the nutritional role played by opportunistic scavenging in storm-petrels and the possible sensory cues facilitating such aggregations. Furthermore, it exemplifies the importance of natural history observations in documenting infrequent but ecologically significant interactions.