Global-scale shorebird distribution in relation to productivity of near-shore ocean waters

The median density of shorebirds during their non-breeding season on the co ast of South America was significantly greater in coastal zones with high p rimary productivity than in zones with moderate and low primary productivit y. A world-wide review showed that sites harboring large numbers of winteri ng and migratory shorebirds corresponded significantly with regions of high coastal zone productivity. We suggest that the spacing of rich intertidal foraging habitats along the world's coastlines has been an important featur e in the evolution of long distance migration by shorebirds.