title: Declines in migrant shorebird populations from a winter-quarter perspective.
abstract: Many long-distance migrating shorebird (i.e., sandpipers, plovers, flamingos, oystercatchers) populations are declining. Although regular shorebird monitoring programs exist worldwide, most estimates of shorebird population trends and sizes are poor or nonexistent. We built a state-space model to estimate shorebird population trends. Compared with more commonly used methods of trend estimation, state-space models are more mechanistic, allow for the separation of observation and state process, and can easily accommodate multivariate time series and nonlinear trends. We fitted the model to count data collected from 1990 to 2013 on 18 common shorebirds at the 2 largest coastal wetlands in southern Africa, Sandwich Harbour (a relatively pristine bay) and Walvis Bay (an international harbor), Namibia. Four of the 12 long-distance migrant species declined since 1990: Ruddy Turnstone (Arenaria interpres), Little Stint (Calidris minuta), Common Ringed Plover (Charadrius hiaticula), and Red Knot (Calidris canutus). Populations of resident species and short-distance migrants increased or were stable. Similar patterns at a key South African wetland suggest that shorebird populations migrating to southern Africa are declining in line with the global decline, but local conditions in southern Africa's largest wetlands are not contributing to these declines. State-space models provide estimates of population levels and trends and could be used widely to improve the current state of water bird estimates.
authors: DST/NRF Centre of Excellence at the Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Rondebosch, South Africa, 7701.
authors: Robert E
authors: RE
authors: Simmons
authors: Directorate Scientific Services, Ministry of Environment and Tourism, Windhoek, Namibia.
authors: Holger
authors: H
authors: Kolberg
authors: Namibian Coast Conservation and Management Project, Ministry of Environment and Tourism, Swakopmund, Namibia.
authors: Rod
authors: R
authors: Braby
authors: Centre for Statistics in Ecology, Environment and Conservation, Department of Statistical Sciences, University of Cape Town, Rondebosch, 7701, South Africa.
authors: Birgit
authors: B
authors: Erni
mesh_terms: D063147:Animal Distribution; D025041:Animal Migration; D000818:Animals; D046091:Charadriiformes / Q000502:physiology*; D003247:Conservation of Natural Resources; D008954:Models, Biological; D009276:Namibia; D011157:Population Dynamics; D012621:Seasons
keywords: Bahía Walvis; Namibia; Puerto Sándwich; Sandwich Harbour; Walvis Bay; declinaciones a largo plazo; long-term declines; modelo de estado-espacio; population trend; state-space model; tendencias poblacionales