Estimation du nombre total des oiseaux aquatiques hivernant en Tunisie : période 2001/2002 à 2006/2007

Abstract

Estimating the total number of wintering waterbirds in Tunisia : period 2001/2002 to 2006/2007 Over the past decades, many waterbird populations have undergone rapid changes in numbers as well as in distribution. These continuing changes make it necessary to update population estimates on a regular basis. From this point of view, a regular mid-winter survey of wintering waterbirds was carried out in Tunisian wetlands. The overall objective of this paper is to record wintering population sizes for the period 2001–2002 to 2006-2007 and to identify waterbird indicator species relative to these Tunisian ecosystems. The preliminary analysis of the collected information enabled us to define the size and the actual status of wintering waterbird populations in Tunisia. A total richness of 106 species (3 common, 18 frequent and 85 rare ones), belonging to 23 families and 10 orders, was identified. The most abundant species, which accounted for about 90 % of the total abundance, were : Calidris alpina (18.7 %), Phoenicopterus ruber (13.6 %), Aythya ferina (11.4 %), Fulica atra (10.7 %), Tringa totanus (5.9 %), Larus michahellis (5.2 %), Larus genei (3.9 %), Anas penelope (3.7 %), Calidris minuta (3.5 %), Anas clypeata (2.2 %), Larus ridibundus (2.0 %), Charadrius alexandrinus (1.9 %), Phalacrocorax carbo (1.6 %), Vanellus vanellus (1.4 %), Pluvialis squatarola (1.3 %), Anas platyrhynchos (1.3 %), Anas crecca (1.3 %) and Numenius arquata (1.1 %). With an average of about 427 300 birds per year, Tunisian wetland areas play an important role in waterbird populations conservation due to their large habitats, high productivity and geographical position connecting European and African continents. Considering the Ramsar Criterions, a total of 20 sites appear as internationally important. Indeed, 3 sites individually and regularly held more than 20 000 birds and should be classified as internationally important : Kneiss islands (72 368 birds per year), Ichkeul National Park (91 587 birds per year), and sebkhat Sejoumi (29 276 birds per year). Together, these wetlands host about 45 % of the total national population sizes. Three other sites are also potentially important, recorded as hosting more than 20 000 wintering birds at least once : Kerkennah islands (16 608 birds per year), Jerba island (14 962 birds per year) and sebkhat Ariana (19 122 birds per year). The 1 % threshold for use in Ramsar Convention was met for 14 species (Sterna sandvicensis, Larus genei, Platalea leucorodia, Grus grus, Charadrius alexandrinus, Phoenicopterus ruber roseus, Pluvialis squatarola, Calidris minuta, Calidris alpina, Tringa totanus, Anser anser, Anas penelope, Aythya ferina and Fulica atra) and was exceeded in 10 wetlands. Among all species, 6 are globally threatened (Marmaronetta angustirostris, Aythya nyroca, Oxyura leucocephala, Gallinago media, Limosa lapponica and Larus audouinii) and were regularly observed in 10 sites. Application of the global ANOVA Kurskal-Wallis test to data relative to species richness, mean abundance and Hill (N1 and N2) diversity values reveals highly significant differences between the 8 wetland classes. However, the spatial organization of aquatic birds doesn’t reflect any clear gradient. The ANOSYM test discriminates two major associations : artificial versus natural habitats. The latter are themselves organized into 3 sub-associations according to permanence of water and marine influences. Despite these important carrying capacities of Tunisian wetlands, natural factors and human exploitation have greatly modified many of these ecosystems through habitat loss and fragmentation. Thus, it appears essential to use appropriate strategies, like indicator species method, to enhance the value of these areas for waterbird species, which are very sensitive to habitat changes. In the present case, based on the SIMPER analyses method, 15 species are indicators of the wetland status : Phoenicopterus ruber, Charadrius alexandrinus, Calidris alpina, Larus michahellis, Ardea cinerea, Bubulcus ibis, Ciconia ciconia, Vanellus vanellus, Grus grus, Phalacrocorax carbo, Larus genei, Fulica atra, Tachybaptus ruficollis, Aythya ferina, Podiceps cristatus and Anas platyrhynchos. Besides their fundamental interest and importance, results of the present study can be essential to the application of conservation programs.