Zwarts L. (1988) Numbers and distribution of coastal waders in Guinea-Bissau. ARDEA 76 (1): 42-55

One million waders overwinter on the intertidal flats of Guinea-Bissau (1570 km2; Fig. 1). Curlew Sandpiper (250,000), Bar-tailed Godwit (156,000), Knot (144,000) and Little Stint (123,000) are the four most common species (Table 1). The estimated totals, based on counts made during the winter of 1982/1983 (81 km2 counted) and the winter of 1986/ 1987 (278 km2 counted), are an improvement on the estimates by Poorter & Zwarts (1984) whose extrapolation was based solely on the counts done during the first winter. The counts were carried out on the low water feeding areas, since high water counts were impracticable. Most waders roosted in mangroves where they were easily overlooked. The preference for roosting in mangroves or on the ground differed per species (Fig. 3). Low tide distribution was related to the type of sediment (Figs 2, 6 and 7) and the presence of the fiddler crab Uca tangeri (Fig. 5). The species composition in and outside the burrowing zone of Uca was completely different (Fig. 4). Whimbrel and Common Sandpiper appear to be typical Uca specialists, whereas the Calidris species and the Bar-tailed Godwit rarely fed on Uca. Female Curlews foraged relatively more inside the Uca zone than males (Fig. 8). Curlews feeding on Uca extracted them from their burrows: the longer the bill the more crabs within reach. The number and biomass of Uca accessible for the short-billed Curlew was so low (Fig. 9) that most of them switched to other prey. Female Bar-tailed Godwits fed mainly along the tidal edge, whereas most males were found on the intertidal flats (Fig. 8). The rare Uca specialists among the Bar-tailed Godwits were the (long-billed) females; prey accessibility IS probably the explanation, as is the case with the Curlew. Sex ratio counts revealed that half of the Curlews and Bar-tailed Godwits in Guinea-Bissau were males. Wader density and predation pressure on the intertidal areas in Guinea-Bissau (Fig. 10) and elsewhere are compared (Table 2, Fig. 11). The Importance of the coastal wetlands in Guinea-Bissau, the geographical origin of the waders and their flyways (Fig. 12) are briefly discussed.