The importance of protected areas as nocturnal feeding grounds for dabbling ducks wintering in western France
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
References (54)
Competitive foraging in mallards: ‘ideal free’ ducks
Animal Behaviour
(1982)- et al.
A review of habitat changes in the Camargue: an assessment of the effects of the loss of biological diversity on the wintering waterfowl community
Biological Conservation
(1994) Patagial tags for waterfowl
Journal of Wildlife Management
(1963)- et al.
Waterfowl Ecology and Management
(1994) Bird Trapping and Bird Banding. A Handbook for Trapping Methods all Over the World
(1991)- et al.
Individual variation in the competitive ability of interference prone foragers: the relative importance of foraging efficiency and susceptibility to interference
Journal of Animal Ecology
(1999) - et al.
A review of the use and the effects of marks and devices on birds
Ringing and Migration
(1992) - et al.
Use of mini-refuges by female northern pintails wintering in southwestern Louisiana
Wildlife Society Bulletin
(1998) - et al.
Dénombrements d'Anatidés et de foulques hivernant en France. Janvier 1995
(1995) - et al.
Dénombrements de cygnes, oies, canards et foulques hivernant en France. Janvier 1996
(1997)
Dénombrements d'Anatidés et de Foulques Hivernant en France. Janvier 1997
Dénombrements d'Anatidés et de Foulques Hivernant en France à la mi-Janvier 1998
The response of bird populations to habitat loss
Ibis
Long-term changes in agricultural practices and wildfowling in an internationally important wetland, and their effects on the guild of wintering ducks
Journal of Applied Ecology
Changes in the frequency of prospecting fly-overs by Marsh harriers Circus aeruginosus in relation to short-term fluctuation in dabbling duck abundance
Ardea
Birds
Tail-mounted radio transmitters for waterfowl
Journal of Field Ornithology
Individual behaviour, populations and conservation
The concept of carrying capacity and shorebirds
How Oystercatchers survive the winter
Interruptions of terrestrial feeding as a way to decrease the non-digestible fraction of the bolus: field observations and laboratory experiments in mallard
Wildfowl
Foraging behavior and habitat choice of wintering Northern Shoveler in a major wintering quarter in France
Waterbirds
The use of an artificial wetland by shoveler Anas clypeata in western France: the role of food resources
Revue d'Ecologie (Terre et Vie)
Activities and food resources of wintering teal (Anas crecca) in a diurnal feeding site: a case study in western France
Revue d'Ecologie (Terre et Vie)
Wetland loss and wintering waterfowl in Greece during the 20th century: a first approach
Feeding ecology of Mallards wintering in Nebraska
Journal of Wildlife Management
An Introduction to Behavioural Ecology
Cited by (77)
Modeling the spread of avian influenza viruses in aquatic reservoirs: A novel hydrodynamic approach applied to the Rhône delta (southern France)
2017, Science of the Total EnvironmentRice and duck, a good combination? Identifying the incentives and triggers for joint rice farming and wild duck conservation
2015, Agriculture, Ecosystems and EnvironmentInfluence of changes in local environmental variables on the distribution and abundance dynamics of wintering Teal Anas crecca
2023, Biodiversity and ConservationSTUDY OF THE ISOTOPIC ECOLOGICAL NICHE OF THE COMMON COOT FULICA ATRA (LAC TONGA, NORTH-EASTERN ALGERIA)
2023, Applied Ecology and Environmental Research