The zonation of non-breeding waterbirds along the Schelde estuary (The Netherlands–Belgium), one of the longest estuaries in NW-Europe with still a complete salinity gradient, including a large freshwater tidal area, was described. Numbers of birds were counted monthly over the period October 1991 to June 1997. Highest numbers of waterbirds were observed in late autumn and winter, with annual peak numbers ranging between 150,000 and 235,000 individuals for the whole estuary. Based on a multivariate analysis different waterbird communities were observed along the salinity gradient. The polyhaline areas of the estuary were numerically dominated by the waders Oystercatcher and Dunlin. Due to the presence of a large brackish marsh in the mesohaline zone, the waterbird community in this area was dominated by the herbivores Wigeon and Greylag Goose. In the oligohaline and freshwater tidal areas, the waterbird community was dominated by duck species, with Teal and Mallard being the most important. The international importance of the Schelde estuary for waterbirds was evidenced by the fact that for 21 waterbird species the 1% level criterion, according to the Ramsar convention, was exceeded. The relation of the observed diversity and community patterns with the functional and habitat diversity of the Schelde estuary as well as the effect of recent conservation measures to preserve this habitat were discussed.

Abstract As the previous chapter discussed, Oystercarcher numbers breeding or wintering in one area may depend not only on factors operating in that area hut also on the supply of birds available to live there. This, in turn, depends on the attractiveness of the area relative to others and on processes occurring on the, often distant, wintering or breeding grounds and on migration. In such a species, population processes must be investigated at large spatial scales. But how large must the scale be before, in some meaningful sense, we can say that a population is being studied? Oystercatcher numbers on one mussel bed, for example, are determined almost entirely by the behavioural decisions of individuals and few would regard investigating this as a population study. But as the scale increases relative to the scale of movement of individuals, numbers become increasingly dominated by the balance between reproductive and mortality rates until all of the important changes in numbers are caused this way. Some ecologists argue that population studies can only be done satisfactorily at the scale at which immigration and emigration arc for all practical purposes non-existent.

The number of waders in the Oosterschelde, S.W. Netherlands, declined after a reduction in intertidal area due to the construction of a storm surge barrier and secondary dams, suggesting that the carrying capacity had been reached (Schekkerman et al., 1993). In this paper we present data on consumption and predation pressure by birds to explore whether the reduction in their numbers is due to prey depletion or to other factors.

Between 1982 and 1987, the construction of a storm-surge barrier and two secondary dams in the eastern and northern parts of the Oosterschelde/Krammer-Volkerak area resulted in the loss of 33% of the 170 km2 of intertidal area in the estuary. Consequences for non-breeding waterbirds were evaluated on the basis of monthly high-tide counts during five seasons before and three seasons after the construction period.

Until a few years ago there was a paucity of ornithological information from the north coast of Egypt, including the Nile Delta lakes. Several recent expeditions to this region revealed new and important information, particularly on quantitative aspects of the Mediterranean coastal avifauna. Systematic counts of migrating waterbirds along the north coast of Sinai have also been carried out during six autumns between 1973 and 198 2 (Paran & Paz 1980, Paran 1980, Y. Paran in lit., Petersen & Sørensen 1980, 1981a, 1981b, Baha el Din & Salama 1984). Counts of waterbirds have been carried out in the Nile Delta lakes in the winters of 1978/79, 1979/80 and in November 1981 (Meininger & Mullié 1981a, 1981b, Bennett et al. 1982). Also, preliminary surveys of breeding birds were made in the spring of 1983 in the Nile Delta lakes (Meininger et al. 1986) and in the spring of 1985 along the north coast of Sinai (Fry et al. 1985).

In the winters of 1978/79 and 1979/80, and in September and October 1980, the authors investigated the trapping and hunting of waterbirds in Lake Manzala (Egypt). It has been calculated that 98 000–162 000 waterbirds are killed annually. The number of people practising these activities is estimated at less than 2000 in a population of 35 000–40 000 fishermen. The majority of the birds are, however, taken by less than 100 men. Compared with 1930 about 30–50% fewer duck and coot are sold. This decrease is mainly caused by the decrease in numbers of pochard and tufted duck. Hunting pressure on waders was found to be extremely high. The contribution of these activities to the regional economy is reviewed and found to be insignificant. A number of conservation measures are recommended.