Avifauna diversity and phenology in a Ramsar site: Lake Tonga (Northeastern Algeria)

Study Extent

The study was carried out at Lake Tonga, a Ramsar site and wilderness area in El Kala National Park (annex 1). Located in the extreme Northeast of Algeria, this freshwater marsh covers an area of 2,600 ha. It occupies a large coastal depression and communicates with the sea by means of an artificial channel (fig. 1). Eighty percent of the park is covered in a mosaic consisting of emergent vegetation composed of helophyte (notably bulrushes, phragmites and typhas), with a large open water area largely occupied by the white water lily Nymphaea alba. This lily is becoming increasingly invasive, especially during the nesting period of the water birds (Lazli, 2011). Lake Tonga is considered the most important wintering and nesting site in North Africa for a multitude of species, such as the white-headed duck Oxyura leucocephala, the ferruginous duck Aythya nyroca, the purple swamp hen Porphyrio porphyrio, the great crested grebe Podiceps cristatus, and the glossy ibis Plegadis falcinellus (Lazli et al., 2011a, 2011b, 2012; Gherib and Lazli, 2016, 2017; Menasria and Lazli, 2017, Mecif et al., 2020). Regarding halieutic diversity, four species have been identified: Barbus callensis, Anguilla anguilla, Gambusia affinis and Pseudophoxinus callensis (Benmetir et al., 2020).The lake also hosts 22 Odonata species and several species of reptiles and amphibians (Lazli, 2011; Gherib, 2018). Despite its international importance and the essential role it plays in maintaining high biodiversity, this wetland is under increasing pressure from issues such as poaching, eutrophication, urbanization, and recreational summer activities, all of which increase the difficulties of carrying out local conservation actions (Lazli et al., 2014; Gherib and Lazli, 2017; Menasria and Lazli, 2017, Mecif et al., 2020).

Sampling

Fieldwork was conducted twice monthly, from September 2013 until August 2016 using a KONUS-SPOT telescope (20 × 60) and a pair of binoculars (10 × 50). We conducted individual counts when the total number of birds was fewer than 200, and made a visual estimate when the number of birds was greater than 200. In this case, we divided the flock into small equal parts and counted the number of birds in each part. This is the most commonly used method in winter counts because the number of individuals and the observation distances are often large (Lamotte and Bourlière, 1969; Blondel, 1975; Tamisier and Dehorter, 1999).
To avoid disturbing the birds, observations were made from the banks, from around the lake, and from natural promontories. We also used the two watchtowers of "Meizila" and "Oued El Hout" as observation points.

Quality Control

To characterize the aquatic avifauna population, we determined several ecological indices, namely: (i) total abundance, which consisted of a count of the total number of birds that visited Lake Tonga on a specific date (Baziz, 2012); (ii) the frequency of occurrence (fi) according to Dajoz (2006) in Elafri et al. 2016, by dividing the number of surveys during which the species was recorded by the total number of conducted surveys; (iii) specific richness, which is the number of bird species observed on a specific date. This also allows determination and characterisation of the periods when bird numbers are richest and poorest (Blondel, 1969; Legendre and Legendre, 1979; Lindström and Piersma, 1993), (iv) Simpson index, D (according to the formula D = 1 − {Σni (ni − 1)/N (N − 1)}, where ni is the total number of birds of each individual species; N is the total number of birds of all species), (v) Shannon and Weaver diversity index H’(according to the formula H′ = [ΣPi ln Pi ], where Pi = is the proportion of each species in the sample (Daget, 1979). H' value varies from 0 when the community is composed of only one species to 4.5 or 5 bits for the most diverse communities. The lowest values, less than 1.5 bits, are associated with communities dominated by 01 or a few species (Faurie et al., 2003); (vi) as well as the Equitability index or Evenness (E) according to the formula H’/ H’ max, where (H′) is the Shannon diversity index and H’ max= lnS, is the maximum diversity and S is the specific richness recorded during each visit. When E is close to 1, the diversity observed reflects an abundance distribution close to equilibrium (Legendre and Legendre, 1979). Conversely, when E is close to 0, the observed diversity is low and illustrates a highly hierarchical distribution of abundance, which reflects a simple, restrictive environment in which few factors structure the settlement (Gherib, 2018).

Method steps

1. With the monitoring of numbers, we visually noted the locations of waterbirds on grid maps, including all species regularly frequenting the lake and its immediate surroundings, whether wintering or nesting. The location of birds across the water body will later allow us to establish a distribution map of bird families observed throughout the wetland. Statistical analyses were carried out using Minitab 17 Ink. Because the data followed a normal distribution, we used the analyses of variance (one-way ANOVA) to determine whether there was a difference in ecological indices between the three years. The significance level used was p < 0.05.

1. Podicipedidae
   rank: family
2. Phalacrocoracidae
   rank: family
3. Ardeidae
   rank: family
4. Ciconiidae
   rank: family
5. Threskiornithidae
   rank: family
6. Phoenicopteridae
   rank: family
7. Anatidae
   rank: family
8. Accipitridae
   rank: family
9. Pandionidae
   rank: family
10. Rallidae
    rank: family
11. Recurvirostridae
    rank: family
12. Charadriidae
    rank: family
13. Scolopacidae
    rank: family
14. Motacillidae
    rank: family
15. Alcedinidae
    rank: family
16. Laridae
    rank: family
17. Falconidae
    rank: family

The study was carried out at Lake Tonga, a Ramsar site and wilderness area in El Kala National Park. Located in the extreme Northeast of Algeria, this freshwater marsh covers an area of 2,600 ha. It occupies a large coastal depression and communicates with the sea by means of an artificial channel. Eighty percent of the park is covered in a mosaic consisting of emergent vegetation composed of helophyte (notably bulrushes, phragmites and typhas), with a large open water area largely occupied by the white water lily Nymphaea alba. This lily is becoming increasingly invasive, especially during the nesting period of the water birds. Lake Tonga is considered the most important wintering and nesting site in North Africa for a multitude of species.