Chance Hines Mitchell Byrd Reese F. Lukei Jr. Barton J. Paxton Laura Duval Keriann Spiewak Gregory D. Kearns Daniel D. Day Barnett Rattner Bryan D Watts 2026 <p class="TitleInline"><strong>Introduction:<span>&nbsp;</span></strong></p><p>Ospreys (<i>Pandion haliaetus</i>) are well-known sentinels of aquatic ecosystem health and are indicators of both environmental contaminants and fish stocks. The Chesapeake Bay supports one of the largest osprey breeding populations in the world, but recent studies have documented declining reproductive performance and increasing food stress in some portions of the estuary.</p><p class="TitleInline"><strong>Methods:<span>&nbsp;</span></strong></p><p>We monitored osprey nests (N = 571) throughout the Chesapeake Bay during the 2024 breeding season and compared breeding metrics between high-salinity (&gt;10 parts per thousand [ppt]) and low-salinity (&lt;5 ppt) study areas. We also compared contemporary breeding performance within four high-salinity sites to historical data collected during the 1980s.</p><p class="TitleInline"><strong>Results:<span>&nbsp;</span></strong></p><p>Salinity was strongly associated with breeding performance and the likelihood that pairs achieved productivity levels required for population maintenance. All high-salinity study areas functioned as demographic sinks, whereas low-salinity areas functioned as demographic sources. Breeding metrics including the proportion of pairs breeding, clutch size, nesting failure, brood reduction, and nestling loss all suggested greater food stress within high-salinity areas. Temporal comparisons documented substantial declines in reproductive performance between the 1980s and 2024 within high-salinity study sites. High-salinity sites during the 1980s exhibited breeding performance comparable to low-salinity sites in 2024.</p><p class="TitleInline"><strong>Discussion:<span>&nbsp;</span></strong></p><p>Although several factors may influence osprey productivity within the Chesapeake Bay, we suggest that reduced availability of Atlantic menhaden (<i>Brevoortia tyrannus</i>) is a primary driver of poor reproductive performance within high-salinity waters.</p> application/pdf 10.3389/fmars.2026.1685158 en Frontiers Media Widespread reproductive deficits in Chesapeake Bay ospreys article