Cross-ecosystem linkages between freshwater insects and riparian birds across the USA.

Freshwater and terrestrial ecosystems are linked by reciprocal flows of energy and nutrients, including the emergence of aquatic insects that provide abundant, high-quality prey for riparian birds. Local studies show that emergent aquatic insects can enhance bird reproduction and survival, yet it remains unclear whether such associations scale up across landscapes and persist under human disturbance. Here we show that the richness of mayflies, stoneflies and caddisflies (Ephemeroptera, Plecoptera and Trichoptera; EPT), an indicator of freshwater integrity and insect emergence, predicts the prevalence of 288 bird species across 14,177 rivers in the contiguous USA, even after accounting for human land use. Aerial insectivorous birds exhibit more than threefold higher prevalence at sites with high compared with low EPT richness. This linkage is consistent across river types describing hydrology (including intermittent systems), temperature and geomorphology, with the strongest gains occurring in rivers with low baseline bird prevalence. The associations are weaker in urbanized sites but persist in highly agricultural landscapes provided that EPT richness remains relatively high. Our findings provide continental-scale evidence that emergent aquatic insects sustain riparian birds, underscoring that freshwater conservation offers considerable co-benefits to terrestrial ecosystems.