Elsevier

Biological Conservation

Volume 103, Issue 2, February 2002, Pages 183-198
Biological Conservation

The importance of protected areas as nocturnal feeding grounds for dabbling ducks wintering in western France

https://doi.org/10.1016/S0006-3207(01)00120-3Get rights and content

Abstract

We studied the diurnal and nocturnal habitat use of wintering dabbling ducks (Anas spp.) in two protected areas of an internationally important winter quarter in western France. The waterbodies of the reserves are heavily used by ducks during daylight hours, and 3–55% of these birds used the reserves at night: >50% of shoveler (A. clypeata), 20% of granivorous ducks (mallard A. platyrhynchos, teal A. crecca and pintail A. acuta), and lower numbers of herbivores (wigeon A. penelope and gadwall A. strepera). Radio-tracking showed that some ducks used the reserves by day and by night, and that some of them may switch from one protected site to another: radio-tagged birds were located in one of the two protected areas for 76% of the days and 81% of the nights they were sought, with granivores switching from waterbodies to wet grasslands within a reserve between the two periods. Such resident individuals may be ‘experienced’ wintering ducks, avoiding surrounding unprotected feeding habitats at night, while birds that leave the reserves at night may be subdominants and/or ‘naı̈ve’ individuals from a transient migratory sub-population. This study suggests that management of nature reserves should combine day-roosts with significant areas of nocturnal feeding grounds, since in protected areas both habitats may be successively used by wintering dabbling ducks across the 24-h cycle.

Introduction

Most wetlands have undergone major changes during the last few decades, despite growing public demand for wildlife conservation and the ratification of the Ramsar convention by many countries. In Europe the principal change has involved habitat loss, especially through drainage for agriculture (e.g. Thomas, 1976, Owen and Thomas, 1979, Poslavski and Shirekov, 1990, Williams, 1990a, Williams, 1990b, Handrinos, 1992, Tamisier and Grillas, 1994, Madsen, 1998). These processes have created a new landscape: a matrix of transformed agricultural landscapes enclosing protected, mostly small, areas. Agricultural fields can attract waterbirds when they provide abundant food (Thomas, 1981, Jorde et al., 1983, Van Roomen and Madsen, 1992, Baldassarre and Bolen, 1994), but the main consequences of agricultural development for waterbirds are negative: loss of habitat increases competitive interactions between individuals and mortality rates (e.g. Goss-Custard and West, 1997). Some birds avoid transformed habitats by modifying their migration routes (Dolman and Sutherland, 1995); nonetheless habitat loss in wetlands generally has severe consequences for waterbird populations (e.g. Goss-Custard and Sutherland, 1997, Weller, 1999). In dabbling ducks (Anatidae), major winter quarters have been abandoned, and large scale redistributions of birds have been reported after wetland transformation (e.g. Pirot and Fox, 1990, Poslavski and Shirekov, 1990, Williams, 1900c, Duncan et al., 1999).

The conservation management of wildfowl habitat, especially for Anas species, is difficult since most dabbling ducks are intercontinental migrants and use contrasting, spatially distinct habitats by day and by night in their winter quarters. The birds generally flock and rest on large waterbodies during daylight hours, and disperse to feed at night into smaller wetlands. Such systems of day-roosts and foraging habitats have been termed ‘functional units’ of dabbling ducks (Tamisier, 1976, Tamisier, 1978).

During the 1970s most of the internationally important winter quarters were marine (Appendix A). Since then several small, newly protected non-marine areas have become very important sites for these birds. For instance, in Charente Maritime the 35,000 ha Marais Littoraux et Côtiers now contain four nature reserves (total area of 400 ha, protected since the 1980s), in inland marshes and coastal lagoons (fresh or brackish, non-tidal) which are currently used by some 15,000 ducks in January (Deceuninck et al., 1999 and pers. comm.). Overall the crude density of ducks is ca. 0.4 birds ha−1, similar to densities in the nearby wintering area, the western part of the Marais Poitevin, 50 km to the north (15,000–20,000 ducks on 40,000 ha, Duncan et al., 1999, Des Touches, pers. comm.). Crude densities in western France are thus of the same order as those in the Camargue, the most important winter quarter for ducks in France (ca. 2 birds ha−1 on 145,000 ha, Tamisier and Dehorter, 1999), but both are much lower than those recorded in the Pacific and Atlantic coasts of America (8–12 birds ha−1, Baldassarre and Bolen, 1994). Nonetheless, the Charente-Maritime wetlands are internationally important for dabbling ducks (>10,000 individuals), and specifically for shoveler and teal.

The protected areas of Charente-Maritime are surrounded by intensive agriculture, and wildfowling takes place both by day and night. This poses particular problems for the conservation and sustainable use of waterbirds, and one major aim of the management of the reserves is to maintain, or create, good feeding habitats within the protected areas (e.g. Salamolard, 1993). There have, however, been few studies of the use of space in these ecological islands (but see Guillemain et al., 2000a, Guillemain et al., 2000b, Guillemain et al., 2000c).

The aim of this paper is to test the prediction that, unlike many other wintering areas, most or all of the birds stay in the protected areas at night. We use duck counts in two protected areas of Charente-Maritime by day, by night and of birds leaving the reserves in evening flights. Radio-marked individuals were followed to determine whether individual ducks specialise, i.e. by remaining in the reserves at night, or by leaving them for feeding habitats in the marshes around, and we describe the types of habitats they use within the reserves at night. The results are discussed in relation to the functional unit principle, and we draw conclusions for the management of nature reserves for these waterbirds.

Section snippets

Study sites

We studied use by ducks of two protected sites of the Marais littoraux et côtiers de Charente-Maritime (Western France, 45°60′ N, 01°00′ W), an area where agricultural drainage has reduced and fragmented the original grazed wet grasslands (Fig. 1). Both sites encompass non-marine day-roosts, surrounded by potential feeding habitats both inside and outside each reserve: these two sites are likely to be distinct functional units for wintering dabbling ducks. The two reserves differ greatly in

Patterns of duck numbers across the winter

Patterns of duck numbers across the winter are shown for each of the six species in Fig. 2. In species where average numbers differed between years, larger numbers were recorded in 1995–1996 than in 1996–97 or 1997–98 (Table 1). The number of mallard at Yves was maximal in early winter, and the numbers relative to the maximum count (hereafter ‘relative number’) decreased linearly from September to March (r2=0.80, F1,28=113.57, P<0.0001; Fig 3). There were two obviously distinct periods at

Habitat use by wintering dabbling ducks

The nocturnal counts showed that both reserves were used at night by a large proportion of the ducks, especially shoveler, of which about half remained in the reserves during the night; at a nearby site of international importance for this species, over half the birds also feed at night on their day roost (Guillemain et al., 2000b). The same pattern, although less pronounced, was also observed in granivorous species: granivores, as predicted in Section 1, used the reserves extensively at night

Acknowledgements

We would like to thank Brian N.K. Davis, Alain Tamisier, John Goss-Custard, Olivier Dehorter and an anonymous referee for valuable comments on an earlier version of the manuscript. We are grateful to Noël and Louis Guillon, Daphné Durant, Emma Fojt, Johanna Corbin, Géraldine Simon, Jérôme Mery, Xavier Fichet, Sylvie Houte and Didier Portron for their help during the field work, as well as Jean-Louis Roland for skilful piloting at night. We thank the Ligue Française pour la Protection des

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