The influence of rivers on seabird foraging ecology.

Rivers act as vital arteries to the world's oceans, delivering fresh water and nutrients that sustain marine ecosystems. Globally, river flow increasingly is being altered by climate change and anthropogenic pressures; yet the significance of rivers to predatory marine species, such as seabirds, and the extent to which river-related changes affect their food webs, remains poorly understood. This review synthesises 51 studies specifically designed to examine river influences on seabird habitat selection, diet, health, and demographics, while highlighting methodological approaches and ecological patterns. Although river-related variables remain underutilised in seabird research, 88% (45/51) of studies that included them reported clear evidence of river effects for at least one type of seabird response, suggesting these ecological links are under-recognised rather than absent. When selected as the primary explanatory (most informative) variable in each study, plume-based metrics were conclusive in 95% (19/20) of cases, whereas river-specific metrics (namely number of rivers, river outflow and distance to river mouths) were conclusive in 84% (26/31) of cases, confirming that both metric types are highly reliable once aligned with the seabird response in question. River-influenced coastal waters consistently supported critical foraging hotspots across all seabird orders, whilst also exposing birds to potential pollutant burdens and altered prey dynamics. Seabird dietary data are a valuable indicator of prey variability associated with river outflows, with greater prey diversity recorded in estuarine habitats compared to marine ones. Rivers exhibited mixed effects under anthropogenic pressures but generally positive influences during climate disturbances, suggesting that seabirds may increasingly depend on riverine environments as buffers against changing marine conditions. We recommend expanding investigations into river impacts on seabird health in tropical systems, incorporating long-term hydrological influences, and prioritising the integration of river-specific and oceanographic data to predict seabird responses more effectively in a rapidly changing world.