Periodic excretion patterns of seabirds in flight

Understanding when and how often seabirds excrete at sea is important for understanding their potential influence on marine ecosystems¹. Whales are known to redistribute nutrients through excretion, the 'whale pump'². Large and widespread populations of seabirds could similarly shape key pelagic ecosystem processes, but such effects cannot be evaluated without basic data on their excretion behavior. Because of the challenges of observing seabirds traveling over the open sea, current knowledge of such effects is restricted to the terrestrial environment, and their excretion characteristics in open ocean are almost entirely unknown. Here, we report our observations of excretions of streaked shearwaters (Calonectris leucomelas) in the open ocean made using a belly-mounted video camera. The streaked shearwaters exhibited a marked tendency to avoid excretion while floating on the sea surface and consistently excreted during flight. Excretion timings showed periodicity, occurring every 4-10 min during daylight hours with inter-event intervals varying within a few minutes. Streaked shearwaters excreted approximately 5% of their body mass per hour, potentially substantial enough to influence flight energetics. Our study opens a path toward evaluating seabirds' contributions to regional nutrient cycles and their epidemiological interactions within marine ecosystems.