Medium‐term changes in coastal bird communities in the Western Cape, South Africa

Abstract

There are few studies of medium-term, quantitative changes in faunal communities in the southern hemisphere. The linear nature of coastlines makes populations of coastal birds easy to count. Repeat surveys of 278 km of coastline in three regions of the Western Cape, South Africa show marked differences in coastal bird community structure over the last 30 years, despite limited human impacts on coastal habitats (mainly increased human disturbance). The total number of birds has not changed, but species richness increased following colonization of the coast by Egyptian geese (Alopochen aegyptiaca, Anatidae) and three species of ibises (Threskiornithidae). Biomass also increased due to greater numbers of large-bodied birds. Contrary to the prediction that large birds are more susceptible to human disturbance, most small birds decreased in abundance. Among waders that breed along the coastline, numbers of African oystercatchers (Haematopus moquini, Haematopodidae) doubled, linked to increased food availability following invasions by alien mussels (Mytilidae). By comparison, numbers of white-fronted plovers (Charadrius marginatus, Charadriidae) decreased by 37% (59% close to Cape Town), at least in part as a result of increasing human disturbance.The greatest decreases occurred among migrant waders (Scolopacidae and Charadriidae), with numbers of the four most abundant species falling by >50%, and both common Calidris species by >90%. Migrant wader populations decreased in all three regions, irrespective of whether surveys were in protected areas or not, suggesting that factors outside the region are driving these trends. Some species may have decreased due to changes in their preferred wintering areas, but others probably reflect population decreases, confirming the generally poor conservation status of migrant waterbirds worldwide.

A synthesis of three decades of socio-ecological change in False Bay, South Africa: setting the scene for multidisciplinary research and management

“…The most common migrant terns feeding in the bay are common terns Sterna hirundo and sandwich terns Thalasseus sandvicensis, both of which breed in Europe. Counts of coastal roosts in False Bay in 2010 were only 20% the size of roosts in 1980, with common terns showing the most marked decrease (from almost 7,000 birds to less than 250; Ryan, 2013).…”

“…Sandy beaches, including reflective, intermediate, and dissipative-intermediate beach types, dominate the northern shoreline of False Bay (Sink et al, 2012; Figure 8). The sandy beaches provide habitat for nesting birds such as the white-fronted plover Charadrius marginatus (Ryan, 2013). In all, 18 macrofaunal and 17 foredune plant species are known for the sandy beaches of False Bay, two-thirds of which are endemic to southern Africa (Harris et al, 2014), although none are unique to the bay.…”

“…In addition, beaches are under threat from ' coastal squeeze', as they are diminishing between a rising sea level (Section 5.4.3) and ongoing coastal developments (Harris et al, 2015). As a result of human impacts, the bay has seen a 59% decrease in the abundance of white-fronted plovers, which nest above the high-water zone (Ryan, 2013), and declines in the abundance of the giant isopod Tylos granulatus, also a high-shore inhabitant (N. Karenyi personal communication). Pollution and fishing practices in False Bay are mainly responsible for the poor condition of the subtidal sediment habitats in the bay, although their impacts have not been quantified.…”

Declines in migrant shorebird populations from a winter-quarter perspective

“…Only the Bar-tailed Godwit and Common Whimbrel showed increases in the South African studies de Villiers 2009). Ryan (2013) similarly reports considerable declines in Calidris sandpipers between the 1980s and 2010s along the Western Cape coast in South Africa.…”

Waders (Aves, Charadriiformes) in a Mediterranean remnant wetland: a year-round pilot study evidences contrasting patterns in diversity metrics

“…Therefore, little research has been focused on the yearly patterns of diversity metrics applied to the whole wader community, here considered as a ecological assemblage (sensu Magurran, 2004). Studies on this topic have strategic implication in wetland conservation since waders are an assemblage of conservation concern per se and as indicators of the state of wet ecosystems (Ryan, 2013).…”