Conserving the World's specialist riverine birds

The ecotone connecting rivers with their riparian zones represents conditions where fluvial processes, abundant resources and reciprocal energetic subsidies have combined over evolutionary time to create multiple opportunities for niche development in a wide range of organisms. Among them, specialist riverine birds are diverse, conspicuous, and widespread globally, but they remain under-researched by both river ecologists and ornithologists. Globally, we identify 69 bird species that have evolved specialized lifestyles along high-gradient, fast-flowing rivers and here we review (i) spatial patterns in their distribution to identify hotspots of diversity; (ii) major threats to their status and (iii) regions that are candidates for their conservation. Only a few species of specialist riverine birds are well known ecologically, hindering understanding of population trends, distribution, and conservation requirements at regional, continental or global scales. Multiple threats include habitat impairments through dams and other water resource infrastructure; land management for agriculture, forestry and urbanization; invasive non-native species; pollution from well-known and emerging sources; and the effects of climate change on flow patterns and thermal regimes. Neither the direct nor indirect effects involved—for example through prey availability or species interactions—have been adequately addressed by ecologists in contrast to birds in terrestrial or marine ecosystems. We identify two urgent needs respectively, (i) to expand interdisciplinary research to understand the ecology of river birds and (ii) to enhance their conservation both through catchment-scale action and by protecting those regions that support threatened species and large species richness, notably in the tropics and sub-tropics.