Long-term declines of wader populations at the Tagus estuary, Portugal: a response to global or local factors?

Abstract

SummaryMigratory wader populations face global threats, mainly related to increasing rates of habitat loss and disturbance driven by human activities. To a large extent, the long-term survival of these populations requires the conservation of networks of sites along their migratory flyways. The Tagus estuary, Portugal, is among the most important wetlands for waders in the East Atlantic Flyway. Annual winter wader counts have been carried in this wetland since 1975 and a monthly roost-monitoring programme was implemented in 2007. Wintering populations of three out of the five most abundant species, Dunlin Calidris alpina, Grey Plover Pluvialis squatarola and Redshank Tringa totanus, showed significant population declines over the past three decades, which are most likely due to the loss and degradation of roost sites as a result of increasing human activity. The situation is unlikely to improve, as a high proportion of the wintering waders use roost sites that are situated in highly urbanised areas with no legal protection. The use of different roost sites by waders is highly variable both temporally and spatially, thus emphasizing the need for a network of good quality roost sites. Additionally, during migration, 60-80% of all the waders of the Tagus estuary concentrate at a single refuge, thus increasing the risk for wader populations during these periods. SumárioAs populações de aves limícolas migradoras enfrentam ameaças globais, maioritariamente relacionadas com a crescente perda de habitat e perturbação humana. Para garantir a sobrevivência a longo-termo destas populações é imprescindível a conservação de uma rede de áreas húmidas ao longo das suas rotas migratórias. O estuário do Tejo, em Portugal, é uma das mais importantes áreas húmidas para aves limícolas na rota Migratória do Atlântico Este. Desde 1975, foram efectuadas contagens anuais de aves limícolas no inverno nesta zona húmida e, em 2007, foi implementado um programa de monitorização mensal dos refúgios de preia-mar. As populações invernantes de três das cinco espécies de limícolas mais abundantes no estuário, o Pilrito-de-peito-preto Calidris alpina, a Tarambola-cinzenta Pluvialis squatarola e o Perna-vermelha Tringa totanus, mostraram tendências significativas de decréscimo nas últimas três décadas, potencialmente devido à degradação e perda de refúgios como resultado da crescente actividade antropogénica. Esta situação poderá deteriorar-se, uma vez que uma grande proporção das aves limícolas invernantes utiliza refúgios em áreas densamente urbanizadas sem qualquer estatuto legal de protecção. A utilização dos diferentes refúgios do estuário do Tejo por aves limícolas tem uma grande variação espacial e temporal, o que reforça a importância da existência de uma rede de refúgios de elevada qualidade nesta área húmida. Durante a migração, 60 a 80% das aves limícolas concentram-se num único refúgio, ficando assim particularmente vulneráveis neste período.

Intertidal biofilm distribution underpins differential tide-following behavior of two sandpiper species (Calidris mauri and Calidris alpina) during northward migration

“…Adding to these concerns, many shorebird species worldwide are experiencing population declines (Wetlands International, 2006). While the reason(s) for the declines are unclear (Thomas et al 2006;Catry et al 2011) shorebird conservation practices have, hitherto, not encompassed the important role that intertidal biofilm is now known to play in shorebird diets, in general, and fuelling breeding migration, in particular. Based on our study, we recommend that environmental assessments for coastal development and conservation strategies for shorebirds need to explicitly consider the physical and biotic processes that produce and replenish biofilm.…”

Wet Grasslands as a Green Infrastructure for Ecological Sustainability: Wader Conservation in Southern Sweden as a Case Study

“…Grazing and traditional hay making on wet grasslands thus expanded, resulting in a cultural landscape favoring waders [31,32]. However, more recently, wet grasslands have been severely reduced [33,34] through a range of human-induced factors including intensification of agriculture [35,36], hydrological changes [33], eutrophication [30,37], land abandonment [38], forest expansion [39,40], urbanization [41], climate change [42] and land management shifts [43,44]. These factors have resulted in land cover changes that has directly and indirectly influenced species' habitats as well as population structure of species assemblages [34,45,46].…”

Long-term population trends reveal increasing importance of a Mediterranean wetland complex (Messolonghi lagoons, Greece) for wintering waterbirds

“…The trends found in this study were compared to similar analyses available for a range of other European countries: Bulgaria (Michev and Profirov 2003), Sweden (Nilsson 2008), Ireland , the Netherlands (Hustings et al 2009), France (Fouque et al 2009), the UK (Calbrade et al 2010), Portugal (Catry et al 2011), the Czech Republic (Musil et al 2011), Denmark, Germany and the Netherlands (Wadden Sea; Van Roomen et al 2012), and as found in this study, the number of increasing species was higher than the number of decreasing species in Bulgaria, Sweden, the Netherlands (part), France, the UK and the Czech Republic. In contrast, decreasing species were in the majority in the Irish and Wadden Sea (German/Danish/Dutch) studies.…”