Abstract

In many migratory bird populations, individuals forgo migrating to the breeding grounds for one or more years and instead 'oversummer' in non-breeding areas. This behaviour occurs among long-distance migratory shorebirds, typically species exhibiting delayed maturity. As the oversummering areas remain poorly described, conservation strategies will be incomplete even in species experiencing ongoing global declines. Oversummering areas could be a weak link in the chain if they are spatially distinct from non-breeding grounds, and used during critical stages throughout individual's lifetime. Here, we present a combining study based on (1) GPS-tracking adult Hudsonian godwits Limosa haemastica oversummering in inland South America, (2) two consecutive seasons of surveys to estimate minimum godwit abundance in that area, and (3) analyses of 13 years of shorebird counts based on the Neotropical Waterbird Census (NWC) in Argentina. Godwits arrived at pampa plain wetlands in early May and spent 5e6 months there. We observed godwits in six out of 44 wetlands surveyed, with a minimum of 366 and 746 godwits counted each survey. Based on frequency of occurrence in NWC, oversummering propensity in Argentina was high for three out of nine Nearctic shorebird species, all of which are of international conservation concern. Despite our limited survey effort, we found several hundred godwits that will likely represent only a small fraction of the population oversummering in this region. Given their delayed maturity, many other long-distance migratory shorebirds may spend large portions of their lives in previously undocumented wetlands while deferring migration. These unrecognized oversummering habitats fall outside the scope of today's conservation efforts for Hudsonian godwits, because they are not spatially nested within the non-breeding grounds, an issue to be studied for other shorebirds. We therefore propose including specific criteria for oversummering areas when designating wetlands of international concern for the conservation of long-distance migratory shorebirds. (C) 2020 The Author(s). Published by Elsevier B.V.