The emergence of avian influenza virus (AIVs) in seabird populations has intensified in recent years, signaling a significant shift in host ecology and transmission dynamics. To address this, this study introduces the Terrestrial Bird-Seabird Co-occurrence Index (TSCI), a novel metric designed to assess the spatial and temporal co-occurrence between terrestrial bird and seabird AIV hosts. The TSCI demonstrates strong predictive performance (AUC = 0.94), capturing over 84.10% of confirmed seabirds AIV cases within global high-risk zones. Based on this, 363 Mha of coastal wetlands (representing 2.44% of global land area) were identified as high-risk terrestrial birds and seabirds contact interface, providing a robust tool for identifying high-risk zones of potential virus spillover at the “terrestrial birds and seabirds contact interface.” Our analysis highlights that temperate coastal regions, particularly in Europe, North America, and East Asia, exhibit high TSCI values. Wetland ecosystems serve as critical hotspots for virus spillover, emphasizing the need for habitat-specific conservation and surveillance strategies. Our study offers a scalable tool to enhance targeted monitoring, guide resource allocation, and inform integrated policies for preventing zoonotic spillover from wild bird reservoirs under the One Health framework.