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Wintering waterbird assemblages in the central part of the Gulf of Gabès in southern Tunisia

  • Faculty of Science of Gabes

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Although the Gulf of Gabès is recognised as an Important Bird Area, several aspects of the ecology of waterbirds inhabiting this area still need to be investigated. We observed how waterbird foraging guilds varied among habitats. In total, 49 species belonging to 16 families were recorded. Winter visitors accounted for 73% of counts. The avifauna was dominated by shorebirds (52% of records), followed by large wading birds (25%), open-water birds (18%) and waterfowl (5%). However, the structure of local waterbird communities and their composition in terms of foraging guilds varied according to habitat type. The bird communities of sandy beaches were dominated by open-water birds, whereas large mudflats were dominated by shorebirds, and wadi estuaries showed a more even representation of foraging guilds. Locally rare species had narrow distributions, whereas locally abundant species were found widely within the gulf. For four species the 1% population level criterion of the Ramsar Convention was exceeded. Overall, our results show that the Gulf of Gabès hosts important numbers of waterbirds with different ecological requirements, which confirms the importance of this gulf as a wintering area for Palearctic waterbirds.
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Journal of African Ornithology
ISSN: 0030-6525 (Print) 1727-947X (Online) Journal homepage:
Wintering waterbird assemblages in the central
part of the Gulf of Gabès in southern Tunisia
Foued Hamza, Abdessalem Hammouda & Slaheddine Selmi
To cite this article: Foued Hamza, Abdessalem Hammouda & Slaheddine Selmi (2016):
Wintering waterbird assemblages in the central part of the Gulf of Gabès in southern Tunisia,
Ostrich, DOI: 10.2989/00306525.2016.1207721
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Wintering waterbird assemblages in the central part of the Gulf of Gabès in
southern Tunisia
Foued Hamza*, Abdessalem Hammouda and Slaheddine Selmi
Département des Sciences de la Vie, Faculté des Sciences de Gabès, Université de Gabès, Gabès, Tunisia
* Corresponding author, email:
Although the Gulf of Gabès is recognised as an Important Bird Area, several aspects of the ecology of waterbirds
inhabiting this area still need to be investigated. We observed how waterbird foraging guilds varied among habitats.
In total, 49 species belonging to 16 families were recorded. Winter visitors accounted for 73% of counts. The
avifauna was dominated by shorebirds (52% of records), followed by large wading birds (25%), open-water birds
(18%) and waterfowl (5%). However, the structure of local waterbird communities and their composition in terms
of foraging guilds varied according to habitat type. The bird communities of sandy beaches were dominated by
open-water birds, whereas large mudflats were dominated by shorebirds, and wadi estuaries showed a more even
representation of foraging guilds. Locally rare species had narrow distributions, whereas locally abundant species
were found widely within the gulf. For four species the 1% population level criterion of the Ramsar Convention was
exceeded. Overall, our results show that the Gulf of Gabès hosts important numbers of waterbirds with different
ecological requirements, which confirms the importance of this gulf as a wintering area for Palearctic waterbirds.
Rassemblements hivernaux chez les oiseaux aquatiques de la zone centrale du Golfe de Gabes en
Tunisie méridionale
Bien que le Golfe de Gabes soit reconnu comme une zone importante pour la conservation des oiseaux, de
nombreux aspects de l’écologie des oiseaux d’eau qui y vivent restent peu connus. Ainsi, l’objectif de ce travail
était de décrire la diversité de l’avifaune hivernante dans ce golfe et d’étudier la variation de sa composition, en
termes de guildes alimentaires, entre les différents types d’habitat qu’abrite cette région. Au total, 49 espèces
appartenant à 16 familles ont été recensées. Les hivernants représentent 73 % des effectifs enregistrés. Cette
avifaune est dominée par les limicoles (52 % des effectifs enregistrés) suivis par les grands échassiers (25 %),
les laridés (18 %) et les canards (5 %). Cependant, la structure des communautés locales et leurs compositions
en termes de guildes varient en fonction de d’habitat. C’est ainsi que les avifaunes des plages sableuses sont
dominées par les laridés, celles des vasières par les limicoles, alors que les estuaires des oueds abritent une
avifaune plus équilibrée. Les espèces localement rares ont une répartition restreinte, tandis que les espèces
localement abondantes ont une large distribution dans le golfe. D’autre part, pour quatre des espèces recensées, le
critère de 1 % de la Convention de Ramsar est atteint. Globalement, nos résultats montrent que le Golfe de Gabes
abrite un effectif important d’oiseaux d’eau ayant des affinités écologiques variées, ce qui confirme l’importance de
ce golfe pour l’avifaune Paléarctique.
Keywords: abundance, foraging guilds, Gulf of Gabès, Tunisia, waterbirds
Understanding the ecological factors affecting waterbird
diversity is a major question in avian ecology, as well as
for conservation purposes (Danufsky and Colwell 2003;
Granadeiro et al. 2007; Liordos 2010). In recent years there
has been a notable decline in many waterbird populations
around the world (Stroud et al. 2004; BirdLife International
2008; Wetlands International 2012). This decline is particu-
larly severe in the Black Sea/Mediterranean flyway, given
that approximately 65% of shorebirds populations have
decreased in this flyway (International Wader Study Group
2003). Initiation of conservation planning in these areas
requires an understanding of the relationships between
waterbird diversity and habitat features, especially in the
most important areas, such as the Gulf of Gabès, in south-
eastern Tunisia (van Dijk et al. 1986; Isenmann et al. 2005).
The Gulf of Gabès offers a mosaic of wetlands and
coastal habitats, including small sandy beaches, large
mudflats and wadi estuaries. Several previous studies
have shown the ornithological significance of this gulf
(e.g. van Dijk et al. 1986; Spiekman et al. 1993; Bos et al.
2001; Hamdi et al. 2008). However, most investigations
focused on monitoring waterbirds inhabiting the largest
mudflats, whereas less attention has been paid to waterbird
assemblages in the other types of coastal habitats. In
recent related works, we have shown that habitat features
and human presence played important roles in shaping
Hamza, Hammouda and Selmi2
waterbird richness and the abundances of individual
waterbird species (Hamza and Selmi 2015; Hamza et al.
2015). However, for a better knowledge of this avifauna
there is a need to investigate further aspects of its diversity.
This paper aims first to provide more information on the
diversity of this avifauna, by describing its composition in
terms of families, migratory status, conservation status and
foraging guilds. Second, we investigate how guild composi-
tion (functional diversity) of waterbird assemblages varies
among the three main gulf habitats.
Material and methods
Study area
Located in south-eastern Tunisia, the Gulf of Gabès
extends from Ras Kaboudia to Elbibane lagoon. It has
the largest tides in the Mediterranean, with tidal amplitude
ranging between 0.8 and 2 m in neap and spring tides,
respectively (Pérez-Domingo et al. 2008). Salinity ranges
from 37.5 to 39.3, and temperature from 13.2 to 26.5 °C
(Ktari-Chakroun and Azouz 1971; Bradaï and Capapé
2001). This gulf is considered one of the most productive
ecosystems in the Mediterranean region (Papaconstantinou
and Farrugio 2000). It is also classified as an Important Bird
Area (Fishpool and Evans 2001) and includes 10 Ramsar
sites, of which the Kneïs islands is a natural reserve (https://
Three main coastal habitats can be distinguished in this
area: (1) sandy beaches with narrow and steep intertidal
zones, (2) large and slightly steep mudflats crossed by
shallow tidal channels and (3) wadi estuaries including one
or more streams crossing saltmarshes and mudflats.
Our work was conducted in the central part of the Gulf
         
          
the south, covering a total of 125 km of coastline (Figure 1).
Fifty study sites, approximately 2.5 km apart, covering the
three habitat types were selected for waterbird surveys
(Figure 1). The mean site area (2 ± 0.4 km²) was calculated
using limits of each sampled site defined by landmarks,
such as tidal channels, sandbanks and saltmarshes.
Data collection
Waterbirds were surveyed from 10 December 2012 to
31 January 2013. This period corresponds with the peak
abundance of wintering waterbirds. Five surveys were
carried out at different dates, so that each site was visited
five times at approximately one-week intervals. All survey
visits were carried out in the morning, during low tide, and
only under suitable meteorological conditions. During each
visit, the observer (F Hamza) was positioned at an elevated
post close to the shoreline and conducted repeated counts
of birds during 30 min, by using binoculars and occasion-
ally a telescope. The highest recorded number of birds
of each detected species was retained. Each survey
represented a counting time of 25 h (30 min × 50 sites) so
that a total sampling effort of 125 h (25 h × five surveys)
was conducted.
The recorded species were classified according to
their migratory status in three categories based on our
prior field experience and on relevant information in the
literature, notably those in Isenmann et al. (2005): resident
(R), regular wintering (RW) and irregular wintering (IW).
A species was considered resident if it could be seen
throughout the year, with evidence of breeding. Regular
wintering species are migratory species that over-winter
and leave at the beginning of the spring. Irregular wintering
species are uncommon species seen occasionally during
winter in the study area.
We also grouped the recorded species into four foraging
guilds according to feeding niche, foraging behaviour
and habitat preferences (Perrins and Ogilvie 1998):
shorebirds, wading birds, waterfowl and open-water birds.
The shorebird guild included tactile surface-foraging
waders (Haematopodidae, Recurvirostridae, Charadriidae,
Scolopacidae and Rallidae, except Eurasian Coot
Fulica atra). Large wading birds comprised long-legged
species that forage on fish and invertebrates in shallow
water (Ardeidae, Threskiornithidae, Ciconiidae and
Phoenicopteridae). The waterfowl guild included swimming
birds (dabblers and divers) that generally feed in wetland
basins (Anatidae, Podicipedidae, Phalacrocoracidae and
Eurasian Coot). Open-water birds are fish-eating and
scavenging seabirds that often catch fish at sea (Laridae,
Sternidae and Procellariidae).
065 130 km
36° N
34° N
32° N
8° E
10° E
Kneïs Islands
Figure 1: Map of the Gulf of Gabès showing the location of study sites
Ostrich 2016: 1–7 3
Finally, the conservation status of each recorded species
was determined according to BirdLife International (2014).
Data analyses
For each recorded species, we determined the rate of site
occupancy as the number of sites where the species was
recorded divided by the total number of sampled sites
(n = 50 sites). We also determined the abundance of each
species in each site as the mean number of individuals
recorded at that site over the five survey visits. The mean
wintering population of each species in the entire study area
was then calculated as the sum of mean local abundances
in each of the 50 sites. We also converted species local
abundances into density values by dividing them by the
areas of the corresponding sites (birds km²). The relation-
ship between average local density and occupancy was then
investigated using Spearman’s correlation coefficient test.
For each site we determined the density of each
foraging guild by summing the local densities of species
belonging to that guild. We also measured the diversity
of the corresponding local waterbird assemblage using
the Shannon index: H =Σ[(ni/Σni)*log2(ni/Σni)], where
ni is the density of guild i in the considered site. The
obtained data were then used to investigate how waterbird
assemblages varied among the three habitats by means of
the non-parametric Kruskal–Wallis test. The Mann–Whitney
test was also used as a post-hoc test for pair-wise compari-
sons between habitats. We also used the c2 test to compare
the relative abundances of the four studied guilds among
the three sampled habitats. In the latter test, data from sites
belonging to the same habitat were pooled together.
All statistical tests and analyses were conducted using
SAS version 8 software (SAS Institute 1999). Means ± one
standard error are reported throughout the manuscript.
Waterbird diversity
A total of 49 species belonging to 16 families were recorded
(Table 1). The families with the highest numbers of species
were Scolopacidae (25% of species), Anatidae (16%)
and Laridae (12%). The most abundant families were
Scolopacidae (41% of birds), Phoenicopteridae (21%)
and Laridae (16%). The most abundant species were the
Dunlin Calidris alpina and Greater Flamingo Phoenicopterus
roseus, which accounted together for 48% of birds recorded.
The great majority of species (47%) had narrow distribu-
tions, as they occurred in less than 20% of sites. The most
widespread species were the Slender-billed Gull Larus genei
and Kentish Plover Charadrius alexandrinus, which occurred
in more than 80% of sites. Moreover, locally abundant
species tended to occur widely while locally rare species
tended to be more localised, as shown by the positive
correlation between the average local density (calculated
across occupied sites) and occupancy (Figure 2).
Concerning migratory status, 11 species were recognised
as resident, 35 were regular wintering species and the three
remaining species were irregular wintering species and
accounted for negligible numbers.
With regard to conservation status, the studied avifauna
was mainly composed of species of Least Concern (47 of
    
species, the Eurasian Curlew Numenius arquata, which
occurred in a large number of sites (68% of sampled sites)
with relatively high numbers (1 054 individuals, 3% of birds).
We also recorded one Vulnerable species, the Marbled Teal
Marmaronetta angustirostris, which was observed in only
one site during a single visit, with a low number (two pairs).
Moreover, for four species, the 1% level criterion of the
Ramsar Convention was exceeded for relevant populations:
Kentish Plover Charadrius alexandrines (3.17%), Eurasian
Spoonbill Platalea leucorodia (4.16%), Greater Flamingo
Phoenicopterus roseus (5.24%) and Slender-billed Gull
Larus genei (1.36%) (Table 1).
Variation in guild composition among habitats
Considering all sampled sites together, we found that the
studied avifauna was dominated by shorebirds, in terms
of both species number (43% of species) and abundance
(52% of birds). Large wading birds were second in
abundance (25%), although they had the lowest number
of species (12%). Open-water birds ranked third in terms
of both species number (18%) and abundance (18%),
whereas the waterfowl guild ranked second in species
number (27%) but last in terms of abundance (5%).
Using the Kruskal–Wallis test, we found that the strength
and direction of the relationship between bird density and
habitat varied among guilds. There were significant habitat
effects on open-water birds, wading birds and waterfowl, but
no significant effect was recorded on shorebirds (respec-
tively: H2 = 20.92, P < 0.0001; H2 = 11.94, P = 0.003;
H2 = 14.58, P = 0.0007; H2 = 0.69, P = 0.71; Figure 3).
Results of the Mann–Whitney test showed that open-water
birds occurred more abundantly in sandy beaches
compared to large mudflats and estuaries, whereas the
difference between the latter habitats was non-significant
(Figure 3a). Waterfowl were significantly more abundant
in wadi estuaries compared to large mudflats and sandy
beaches, with a non-significant difference between the latter
habitats (Figure 3b). For wading birds, significant differences
were found between pairs of habitats, with wadi estuaries
ranked first, followed by large mudflats (Figure 3c).
Waterbird communities of sandy beaches were
dominated by open-water birds, whereas communities
in large mudflats and wadi estuaries were dominated by
shorebirds, with wadi estuaries having the most even distri-
bution among foraging guilds. This finding is also supported
by the results of the comparisons of waterbird diversity,
measured by the Shannon index, among habitats (Kruskal–
Wallis test: H2 = 17.80, P = 0.0001; Figure 4). The highest
waterbird diversity was recorded in wadi estuaries and the
lowest waterbird diversity in sandy beaches (Figure 4).
The main goal of this work was to describe the diversity of
waterbirds wintering in the central part of the Gulf of Gabès,
with a particular focus on the variation in guild composition
among habitats. Our results first show that the studied area
hosts an important wintering waterbird community, in terms
of both species richness and abundance. This community
is clearly dominated by winter visitors. Even though our
Hamza, Hammouda and Selmi4
Family Common name Scientific name Migratory
Mean density
(birds km²)
Haematopodidae Eurasian Oystercatcher Haematopus ostralegus W LC 48 738 10.423 ± 1.973
Recurvirostridae Pied Avocet Recurvirostra avosetta W LC 2 1 0.002 ± 0.002
Black-winged Stilt Himantopus himantopus R LC 4 5 0.119 ± 0.071
Charadriidae Common Ringed Plover Charadrius hiaticula W LC 42 86 1.457 ± 0.482
Grey Plover Pluvialis squatarola W LC 68 833 9.653 ± 2.015
Kentish Plover Charadrius alexandrinus* R LC 88 2094 26.099 ± 3.872
 Vanellus vanellus W LC 2 1 0.006 ± 0.006
Scolopacidae Dunlin Calidris alpina W LC 66 8739 71.550 ± 24.376
Sanderling Calidris alba W LC 44 411 33.450 ± 9.970
Little Stint Calidris minuta W LC 22 101 2.122 ± 0.590
Bar-tailed Godwit Limosa lapponica W LC 2 9 0.084 ± 0.081
Marsh Sandpiper Tringa stagnatilis W LC 58 122 1.534 ± 0.330
Spotted Redshank Tringa erythropus W LC 30 332 2.602 ± 1.202
Common Greenshank Tringa nebularia W LC 58 112 1.551 ± 0.349
Common Redshank Tringa totanus R LC 30 2211 14.840 ± 6.672
Terek Sandpiper Xenus cinereus W LC 2 1 0.003 ± 0.003
Eurasian Curlew Numenius arquata W 68 1054 10.753 ± 2.526
Ruddy Turnstone Arenaria interpres W LC 18 23 0.247 ± 0.076
Common Snipe Gallinago gallinago W LC 4 1 0.032 ± 0.019
Rallidae Common Moorhen Gallinula chloropus R LC 4 7 0.243 ± 0.152
Water Rail Rallus aquaticus W LC 2 1 0.011 ± 0.011
Rallidae Eurasian Coot Fulica atra W LC 4 72 3.665 ± 2.627
Podicipedidae Great Crested Grebe Podiceps cristatus W LC 48 60 2.247 ± 0.852
Little Grebe Tachybaptus ruficollis R LC 8 20 0.992 ± 0.632
Black-necked Grebe Podiceps nigricollis W LC 30 86 2.069 ± 0.854
Phalacrocoracidae Great Cormorant Phalacrocorax carbo W LC 72 497 13.330 ± 4.509
Anatidae Eurasian Wigeon Anas penelope W LC 16 598 7.515 ± 4.152
 Anas acuta W LC 16 166 1.672 ± 0.722
 Anas clypeata W LC 10 57 1.253 ± 0.690
Gadwall Anas strepera W LC 4 12 0.649 ± 0.472
Mallard Anas platyrhynchos R LC 6 43 0.652 ± 0.428
Common Shelduck Tadorna tadorna R LC 14 37 0.371 ± 0.220
Marbled Teal Marmaronetta
W VU 2 1 0.046 ± 0.031
Red-crested Pochard Netta rufina IW LC 2 1 0.009 ± 0.009
Wading birds
Ardeidae Little Egret Egretta garzetta R LC 46 196 2.433 ± 0.752
Grey Heron Ardea cinerea W LC 72 379 5.153 ± 1.055
Great Egret Egretta alba W LC 34 178 0.948 ± 0.290
Ciconiidae Black Stork Ciconia nigra IW LC 2 1 0.009 ± 0.006
Threskiornithidae Eurasian Spoonbill Platalea leucorodia* W LC 58 499 3.741 ± 0.818
Phoenicopteridae Greater Flamingo Phoenicopterus roseus* W LC 56 6815 48.167 ± 8.454
Open-water birds
Laridae Slender-billed Gull Larus genei* R LC 84 2338 97.005 ± 27.584
Yellow-legged Gull Larus michahellis R LC 76 1404 68.732 ± 43.429
Herring Gull Larus argentatus IW LC 2 1 0.008 ± 0.008
Lesser Black-backed
Larus fuscus W LC 58 798 38.613 ± 10.599
Black-headed Gull Larus ridibundus W LC 34 596 47.647 ± 24.988
Mediterranean Gull Larus melanocephalus W LC 8 128 7.894 ± 5.687
Sternidae Caspian Tern Sterna caspia W LC 60 116 3.568 ± 0.955
Sandwich Tern Thalasseus sandvicensis R LC 28 272 10.490 ± 4.869
Procellariidae Cory’s Shearwater Calonectris diomedea IW LC 4 1 0.142 ± 0.101
* Species exceeding the 1% level criterion of the Ramsar Convention
Table 1: List of recorded species classified by foraging guild and family, with information on their migratory status, conservation status, site
occupancy rate, estimated population size (calculated as the mean number of recorded birds in the entire study area over the five surveys),
and mean density (±SE). Migratory status: IW = irregular wintering, R = resident, W = wintering; conservation status: LC = Least Concern,
== Vulnerable
Ostrich 2016: 1–7 5
sampling did not cover the entire gulf, we found that for
four species, namely the Eurasian Spoonbill, Greater
Flamingo, Kentish Plover and Slender-billed Gull, the 1%
level criterion of the Ramsar Convention was exceeded
for relevant populations. Moreover, the Eurasian Curlew,
      
area with relatively high numbers. These findings confirm
the status of the Gulf of Gabès as an important wintering
area for Palearctic waterbirds (van Dijk et al. 1986; Hamdi
et al. 2008), as well as an important area for the resident
Slender-billed Gull.
With regard to the patterns of species occurrence, our
results show that the majority of species had narrow distri-
butions within the gulf. They also show that locally abundant
species tended to range widely, whereas locally rare
species had narrow distributions. This trend is consistent
with one of the most recognised rules in community
ecology, namely the positive interspecific abundance–distri-
bution relationship (Hanski 1999; Gaston et al. 2000; Webb
et al. 2007).
The comparison of our survey results with historical
data on wintering waterbirds in the Gulf of Gabès, notably
those published by van Dijk et al. (1986) who also surveyed
waterbirds during the winter period, were confounded by the
differing extents of the surveys. Our surveys were carried
out in the central part of the Gulf of Gabès, whereas van
Dijk et al. (1986) also monitored peripheral areas, which
permitted them to include more large mudflats in their site
sample but did not take into account small sandy beaches.
The relationship between habitat type and bird density
showed guild-specific habitat effects, which is consis-
tent with recent findings on the determinants of wintering
waterbird richness in the same area (Hamza and Selmi
2015; Hamza et al. 2015). Waterfowl occurred more
abundantly in wadi estuaries compared to large mudflats
and sandy beaches, which can be explained by the
123 4
y = 0.8432x − 0.3324
r2 = 38%, P < 0.0001
Figure 2: Relationship between mean density (expressed as
birds km² and calculated using only data from the sites where the
species was recorded) and occupancy rate (%). Both variables
were log-transformed to meet the normality condition. The
regression line and equation are provided
Z = 1.94, P = 0.02
Z = 3.77, P < 0.0001
Z = 1.51, P = 0.07
Sandy beaches Large mudflats Estuaries Sandy beaches Large mudflats Estuaries
DENSITY (birds km−2)
Z = 1.09, P = 0.27
Z = 4.24, P < 0.0001
Z = −3.54, P = 0.0002
Z = 0.28, P = 0.39
Z = 0.93, P = 0.17
Z = 0.05, P = 0.48
Z = 2.92, P = 0.001
Z = −2.46, P = 0.006
Z = 3.78, P < 0.0001
1 000
1 500
0 0
0 0
(a) (b)
(c) (d)
Figure 3: Densities of open-water birds (a), waterfowl (b), wading birds (c) and shorebirds (d) in the three sampled habitats
Hamza, Hammouda and Selmi6
presence of large and deep tidal channels in this habitat
providing attractive roosting and feeding sites. Further
features of wadi estuaries seem to make them more attrac-
tive to waterfowl, in particular the presence of freshwater
for preening and drinking. Moreover, in estuarine habitats
channels were vegetated with dense beds of seagrass,
which seems to be attractive to some waterfowl species,
especially the Eurasian Wigeon, the most abundant species
in this guild and known to feed on seagrass exposed during
Wadi estuaries also provided the most attractive habitat
for wading birds, which also occurred abundantly in large
mudflats. Like the wadi estuaries, large mudflats are
crossed by tidal channels and contain many tidal pools that
retain a thin layer of water at low tide (Hamza et al. 2014).
These tidal channels seem to provide a refuge to juvenile
fishes from predator fishes (Shenker and Dean 1979; Reis
and Dean 1981; Boesch and Turner 1984; Paterson and
Whitfield 2000). During low tides these small fishes provide
highly concentrated feeding opportunities for wading
birds. By contrast, sandy beaches are characterised by
their narrow and steeply inclined intertidal zones. In these
habitats, only a limited intertidal area is available to use as
a feeding ground. Moreover, tidal pools and channels are
absent and the sandy sediment does not host important
invertebrate biomass (Zwarts 1988; Yates et al. 1993;
Hamza et al. 2014), which makes this habitat less attrac-
tive to waterfowl and wading birds (Hamza and Selmi 2015;
Hamza et al. 2015).
Our results also showed that open-water birds occurred
more abundantly along sandy beaches compared to the
other habitats (Hamza and Selmi 2015). This habitat is
commonly used by local artisanal fishermen (Romdhane
1998; FAO 2011), and it seems that open-water birds
have learnt to profit from this artisanal fishing activity. For
instance, terns were commonly seen catching small fishes
stranded in the nets. Moreover, after fishing, fishermen
generally discard large quantities of small fish, crabs and
fish parts that are attractive to large numbers of gulls.
We found that local density of shorebirds did not vary
significantly among habitats. Some of the most abundant
species in this guild, such as Kentish Plover and Eurasian
Oystercatcher, are habitat generalists (Zwarts 1988;
Granadeiro et al. 2007; Liordos 2010). Moreover, this guild
included some species with different habitat requirements
and showing different abundance patterns (Hamza et al.
2015). For instance, unlike the other shorebird species, the
Sanderling occurred more abundantly on sandy beaches
(Hamza et al. 2015), where it feeds on small invertebrates
by pursuing receding waves and snatching items washed in
by tide along wave-break zones (Evans et al. 1980).
Our results also showed that waterbird diversity was
higher in wadi estuaries compared to mudflats and sandy
beaches. This is likely related to the higher diversity and
availability of food resources and micro-habitats offered
by estuaries. They also offer large and permanent water
basins, providing suitable feeding and roosting sites. They
also provided a mosaic of muddy and sandy sediments,
allowing high numbers of shorebirds with different habitat
requirements to coexist. Investigations of factors affecting
the abundance of individual species have also led to the
same conclusion (Hamza et al. 2015).
In summary, our results confirm the importance of the
Gulf of Gabès as a wintering area for Palearctic waterbirds.
They also show that small sandy beaches mainly hosted
open-water birds, whereas waterbird assemblages in wadi
estuaries were more evenly distributed across guilds.
Further investigations of intra-guild habitat partitioning and
interactions between species, such as competition and
commensalism, are needed to better understand the spatial
organization of this avifauna. It would also be necessary to
investigate the responses of waterbird species to human
activity, particularly traditional clam harvesting and fishing,
and the effect of these activities on waterbird diversity. Such
information may be of great relevance for drawing a clearer
picture about the dynamics of waterbirds wintering in the
Gulf of Gabès, as well as for conservation purposes.
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Associate Editor: Michel Louette
... The gulf of Gabès in Tunisia (hereafter GG) is one of the most important foraging and staging areas for many waterbird species in this flyway (Van Dijk et al., 1986;Bos et al., 2001). More than 80 species of birds, including shorebirds, wading birds, gulls and ducks, use the intertidal areas of this gulf as wintering area (Van Dijk et al., 1986;Bos et al., 2001;Hamdi et al., 2008;Hamza et al., , 2016. A total of 190,000 waterbirds overwinter in this area (Hamdi et al., 2008). ...
... Surprisingly, the diversity of seabirds does not increase with the density of artisanal fishermen despite the large quantities of small fish they discard. A previous study in the same coastal area has shown a positive effect of artisanal fishermen on the abundance of seabirds (Hamza et al., 2016). The lack of positive effect of artisanal fishermen on the diversity of seabirds can be explained by the presence of generalist species (Duhem et al., 2008;Ramos et al., 2011;Scott et al., 2015;Mendes et al., 2018), such as Yellow-legged Gull Larus michahellis and Black-headed Gull Larus ridibundus, which are known to use different habitats/resources (e.g. ...
The accelerated human population growth throughout the world is putting much strain on coastal zones. Human activities conducted in coastal wetlands constitute a serious threat to waterbirds. Indeed, quantifying the impact of these activities on waterbird diversity is vital for the implementation of effective management plans. Here, survey data from the central part of the Gulf of Gabès in Tunisia were used to investigate the impact of recreationists, artisanal fishermen and clam-harvesters on the diversity of shorebirds, wading birds, waterfowl as well as seabirds. The results show that recreation activities have a negative effect on both shorebirds and wading birds. However, artisanal fishing has a negative effect on wading birds only. Shorebirds diversity was lower in intertidal areas used for recreation activity, whereas wading birds' diversity was lower in coastal wetlands used for recreation and artisanal fishing. Clam-harvesting had a neutral impact on waterbirds as these birds seem to be habituated to artisanal clam-harvesters and do not perceive them as a threat. To mitigate the negative impacts of human activities, it is important to raise public awareness (e.g. make awareness campaigns, produce leaflets and signs) and to create coastal protected areas.
... Not only the Pannonian Spoonbill population winters in Tunisia but a sizeable part of the Czech, Italian, and the Camargue population as well, and a few individuals from the Danube Delta (Romania), Greece, and the Netherlands (Azafzaf et al. 2006, Smart et al. 2007, Cepak 2008, Volponi et al. 2008, Lok et al. 2011, Blanchon et al. 2017, Pigniczki 2017b, Kiss et al. 2019. Spoonbills find perfect foraging possibilities in the tidal area of the Gulf of Gabes, where the tidal range of up to 2 m is unique for the Mediterranean Sea (Smart et al. 2007, Hamza et al. 2016. From the nature conservation approach, it is an important result that a significant part of the Pannonian Spoonbill population winters in the Gulf of Gabes, which shows the importance of that area at an international level. ...
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In this paper, the wintering characteristics of the Eurasian Spoonbill (Platalea leucorodia) breeding in the Carpathian Basin (Pannonian population) were analysed. The data of 305 wintering Spoonbills marked with colour-rings in Hungary were used. A significant part, 80% of the Spoonbills wintered in Africa, while 20% spent the winter in Europe and only two birds in the Asian part of western Turkey. The most important wintering sites were in the central part of North Africa (in Algeria, Libya, but mainly Tunisia) and Italy. The tidal area in the Gulf of Gabes in Tunisia was the most important area where a significant proportion, 65% of all wintering Spoonbills spent the winter. This study provided new evidence of Spoonbills occurring in Saharan wetlands (Chott Tindla in Algeria) in winter. 2% of the resighted Spoonbills were reported from the wetlands of the Sahel in Sudan, Nigeria, Niger, Mali, Mauritania, and Senegal. European winterers were mainly found in Italy and, to a lesser extent, in the Balkans and the Carpathian Basin. The mean distance between the natal colonies and the wintering areas was 1,535 km. Spoonbills migrated in a south-southwestern direction (mean: 213°) to reach their wintering sites. In the Hungarian population, most specimens (94%) were short-distance migrants (wintered north of 22°N), 2% were long-distance migrants, and 4% were residents. However, the proportions of the residents and short-distance migrants are supposed to be overestimated and the proportion of the long-distance migrants is likely to be underestimated due to the lack of observation effort in sub-Saharan Africa. However, based on the winter census data and the proportion of ringed individuals of Hungarian origin in the wintering flocks, I estimated that the lack of observation effort would only slightly modify the result. There were two shifts in migratory strategies on an individual level: a resident Spoonbill became a short-distance migrant, and a short-distance migrant became a long-distance migrant by a following winter. While most of the East Atlantic Spoonbills are long-distance migrants, the results of this study indicate that most birds in the Pannonian population are likely to be rather short-distance migrants. The results of the GPS tracking also confirm that most Pannonian Spoonbills are short-distance migrants and support the main conclusion of this paper.
... Therefore, numerous studies on habitat use, selection and community organization have been conducted worldwide (e.g. Jones 2001;Hamza et al. 2016;Elafri et al. 2017;Farinós-Celdrán et al. 2017;Chatterjee et al. 2020). Liordos (2010) described the structure of the waterbird assemblage at Vourkari during winter, by assigning species to foraging guilds. ...
Full-text available
Background Small coastal wetlands are vital sites for wintering waterbirds. Identifying important habitats is critical for managing waterbirds effectively. The Vourkari inlet is a small coastal wetland located near the capital Athens, within the most urbanized and industrialized area of Greece. We aimed at identifying the most important habitats for waterbirds at the Vourkari inlet during winter. Methods Data about habitat use and availability were collected for 14 waterbird species and for seven habitat classes. Habitat selection (Manly’s selection ratio), overlap indices (Pianka’s niche overlap index) and null models were calculated. Results All the studied waterbird species selected available habitats nonrandomly. Shallow waters (0–2 m), were used by 13 waterbirds and selected by five waterbirds. Pools and channels were used and selected by 10 species. Mud was used by nine species and selected by six species. Mud with rocky substrate was used by nine species and selected by eight species. Medium (2–4 m) and deep (4–6 m) open water habitats were used by seven species and selected by four species. Halophytic vegetation was used by six species and selected by two species. Several habitats were selected by nationally important populations: mudflat habitats (i.e., mud, mud with rocky substrate and pools and channels) by Common Redshanks ( Tringa totanus ), halophytic vegetation by Little Egrets ( Egretta garzetta ), shallow waters by Common Shelducks ( Tadorna tadorna ) and medium and deep waters by Sandwich Terns ( Thalasseus sandvicencis ), whilst shallow waters and mudflat habitats were preferred by a possibly internationally important population of Mediterranean Gulls ( Ichthyaetus melanocephalus ). Although overlap in habitat use between species was generally low, null models indicated habitat sharing and a lack of competition. Conclusions Waterbirds coexisted in the absence of competition for habitats at Vourkari, where they mostly used and preferred shallow water and mudflats. Small coastal wetlands are numerous, both in Greece and worldwide, therefore our findings would be useful as a basis for comparisons, both temporal at the inlet and spatial with other sites, that would help assess the importance of habitats and improve management strategies to benefit waterbirds, especially in areas with similar Mediterranean-type habitats and climate.
... Ens et al., 1992;Meire, 1996;Schwemmer & Garthe, 2011;Schwemmer et al., 2016). little attention has been paid to north African coastal areas despite there being some important sites within this region, such as the Gulf of Gabès in southern Tunisia (Hamza & Selmi, 2015;Hamza et al., 2016). The intertidal flats of the Gulf of Gabès are known to host more than half of the Mediterranean population of wintering oystercatchers (Van Dijk et al., 1986). ...
Understanding ecological factors and processes affecting the abundance of species of conservation concern is key to ensuring their conservation. The Eurasian Oystercatcher Haematopus ostralegus is a ‘Near Threatened’ wader species that depends on coastal zones during the non-breeding season. However, these habitats constitute focal points of human settlement and suffer from intensified human activities. I used survey data from the central part of the Gulf of Gabès, Tunisia, to assess the significance of ecological and anthropogenic factors as predictors of the density of wintering oystercatchers. Using generalized linear mixed models, Oystercatcher density was positively correlated with sediment mud content and negatively correlated with seagrass cover. Density was also positively correlated with distance from human settlements and negatively correlated with the densities of recreationists and artisanal fishermen. Overall, oystercatchers avoid intertidal areas near human settlements. This study provides critical information on where conservation and research efforts should be focused to preserve this wader species. As a priority, investigations on flight initiation distances are needed to determine at which spatial level it would be beneficial to create buffer zones or walkways to minimise the negative impact of human disturbance on this wintering population.
During two wintering seasons (2013/2014 and 2014/2015) we studied the ecological status and the diurnal behavior of two sensitive dabbling ducks, the Northern shoveler (Anas clypeata) and the Eurasian teal (Anas crecca) at an unprotected and a patchy wetland of northeastern Algeria (the El Feid marsh, 105 hectare). The spatiotemporal distribution of these ducks in the site is mainly controlled by the temporal changes in the water levels and the variations of the wetland size which are both influenced by rainfall rates. Indeed, this distribution is also related to the biological and the life history factors of each species. During the two winters we found that both species are largely presented in this wetland, and high abundance values have been recorded (580 individuals of Northern shoveler and 690 of Eurasian teal; max observed). Arrival and departure of these species are largely similar and both of them reach their maximum populations size at November and February which correspond to the period of high rainfall rates. In this wetland shovelers and teals behave similarly; they spent almost all of their diurnal time roosting (included sleeping and resting with respectively 43% and 54% of their time). Followed by feeding (respectively 27% and 23% of their time), and swimming (respectively 20% and 17%). Such results ascertained that wetlands of this category (patchy and unprotected) function as roosting and foraging sites for migratory and staging dabbling ducks. This fact should change the prevailing attitude that wetlands of this category are of secondary importance for migratory waterbirds (including the Northern Shoveler and the Eurasian teal) and thus should be useful in reducing their degradation and loss. KEYWORDS: Anatidae; diurnal behavior; spatiotemporal distribution; unprotected wetlands; patchy wetland; water regimes
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The Gulf of Gabès, in south-eastern Tunisia, is one of the most important Mediterranean wintering areas for the Greater Flamingo Phoenicopterus roseus. However, information on the ecological factors shaping the abundance and distribution of this species in this wintering area are lacking. During the winter of 2010-2011, we conducted repeated counts of flamingos in fifteen sites in the central part of the Gulf of Gabès. The collected data were used to investigate the abundance and distribution of flamingos in this particular wintering area. We found that the total number of flamingos inhabiting the studied area ranged from 262 to 1781, and the proportion of occupied sites varied between 27 and 80%. We also found that the abundance and distribution of flamingos showed a peak between mid-November and mid-January. After this period, the flamingos became gradually rare, as a result of adults' migration to northern breeding areas. In addition, our results showed that flamingos more frequently and more abundantly occurred in large mudflats (bays and estuaries) than in sandy beaches with small intertidal zones. The formers are likely to present more attractive feeding habitats because of their higher prey availability and accessibility. However, human presence (fishermen and shellfishers) did not appear to affect flamingos' abundance and distribution. Fishermen and shellfishers did not seem to constitute a threat or a major disturbing factor for flamingos.
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Understanding ecological factors and processes affecting waterbird abundance is a major question in ecology and important for conservation purposes. In the Mediterranean, studies dealing with the determinants of waterbird abundance and distribution have mainly been concerned with European coastal habitats, whereas less attention has been paid to coastal areas in North Africa. In this work, we used count data to investigate the relevance of habitat features and human presence as predictors of the abundance of shorebirds and wading birds wintering in the Gulf of Gabès, a particularly important wintering quarter for many Palearctic waterbirds in Tunisia. We found that the strength and direction of the relationships between bird abundance and both habitat and human parameters varied among species, depending on their ecological requirements. Most species occurred more abundantly in large mudflats compared to narrow sandy beaches, while one species showed an opposite trend. We also found that the studied sites were frequently visited by local people, mainly for clam harvesting, thus sharing the intertidal habitats with birds. However, the abundance of most species did not decrease with increasing human presence, suggesting that traditional clam-harvesting activity did not seem to disturb birds. Nonetheless, we believe that further investigations of the interactions between birds and clam-harvesters are needed to better understand the role of traditional clam-harvesting activity in shaping the abundance and diversity of waterbirds wintering in the Gulf of Gabès.
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Les résultats ornithologiques de quatre années d’étude des oiseaux d’eau hivernants dans le golfe de Gabès (2001-2004) montrent un total de 90 espèces, 13 familles et 7 ordres. Les Charadriiformes constituent le groupe taxonomique le plus abondant et le plus diversifié. Le site constitue le quartier d’hiver le plus important à l’échelle nationale et internationale. Sous l’effet contraignant de l’activité humaine et de la diminution de la productivité du site, la majorité des espèces dominantes révèle une baisse remarquable de leurs effectifs.
Captures of the giant devil ray, Mobula mobular, in the Gulf of Gabes (Southern Tunisia, Central Mediterranean). The authors report captures of the giant devil ray, Mobula mobular in the Gulf of Gabes (Southern Tunisia, Central Mediterranean). They discuss the distribution of the species off the Tunisian coasts and in the Mediterranean.
We examined winter (November–January) shorebird use at 19 sites around Humboldt Bay, California, an important site for nonbreeding shorebirds. We analyzed species richness (number of species), species densities, and incidences (presence/absence) in relation to habitat characteristics (tidal flat width, channelization, standing water, timing of tidal ebb, and sediment particle size). We included site area in analyses of incidence, and site area and substrate heterogeneity in the species richness analysis. We observed a total of 19 species, 8–16 at individual sites, and this variation correlated with substrate heterogeneity. Substrate particle size correlated positively with Sanderling (Calidris alba) incidence and negatively with American Avocet (Recurvirostra americana) incidence. Amount of standing water correlated positively with Whimbrel (Numenius phaeopus) and negatively with dowitcher (Limnodromus griseus and L. scolopaceus) incidence. Width of tidal flat correlated negatively with Whimbrel incidence. Sites at which tides ebbed earliest had higher incidences of Whimbrel and Sanderling and higher densities of Long-billed Curlew (Numenius americanus), but lower yellowlegs (Tringa melanoleuca and T. flavipes) densities. The amount of channelization correlated positively with curlew densities. These habitat relationships suggest that alteration of tidal flats at Humboldt Bay and elsewhere in coastal habitats has the potential to adversely affect patterns of shorebird distribution. Comunidades Invernales de Aves Playeras y Características del Plano Mareal en Humboldt Bay, California Resumen. Examinamos el uso invernal (noviembre–enero) de 19 sitios alrededor de Humboldt Bay, California, por parte de aves playeras. Ésta es un área importante para aves playeras no reproductivas. Analizamos la riqueza (número), densidad e incidencia (presencia/ausencia) de especies con relación a características del hábitat (ancho del plano mareal, canalización, agua estancada, momento de la disminución de la marea y tamaño de partículas del sedimento). Incluimos el área del sitio en los análisis de incidencia y el área del sitio y la heterogeneidad del sustrato en los análisis de riqueza de especies. Observamos un total de 19 especies (8–16 en sitios individuales), y esta variación se correlacionó con la heterogeneidad del sustrato. El tamaño de las partículas del sustrato se correlacionó positivamente con la incidencia de Calidris alba y negativamente con la de Recurvirostra americana. La cantidad de agua estancada se correlacionó positivamente con la incidencia de Numenius phaeopus y negativamente con la de Limnodromus griseus y L. scolopaceus. El ancho del plano mareal se correlacionó negativamente con la incidencia de N. phaeopus. Los sitios en que las mareas menguaron más temprano presentaron mayores incidencias de N. phaeopus y C. alba, y mayores densidades de Numenius americanus, pero menores densidades de Tringa melanoleuca y T. flavipes. El grado de canalización se correlacionó positivamente con las densidades de N. americanus. Estas relaciones de hábitat sugieren que la alteración de planos mareales en Humboldt Bay y en otros hábitats costeros potencialmente puede afectar adversamente los patrones de distribución de las aves playeras.
The utilization of an intertidal salt marsh creek in South Carolina during January 1977 was determined by sampling every third ebb tide for 13 days. All fishes leaving the creek during that period were captured in a channel net. This procedure produced a time-series of samples which permitted analysis of the fish community occupying the intertidal creek at all times of day and night. A total of 14,730 larval, juvenile, and adult fishes comprising at least 22 species in 16 families were collected. The most common larval and juvenile fishes were Leiostomus xanthurus, Mugil spp., Myrophis punctatus leptocephali, Lagodon rhomboides, Paralichthys spp., and Micropogon undulatus. Catch sizes for all species varied widely between samples. No diurnal-nocturnal pattern in catches was evident for L. xanthurus, Mugil spp., L. rhomboides and M. undulatus. M. punctatus was taken in large numbers only when the flood tide occurred during the day, while more Paralichthys spp. larvae were taken in late afternoon-evening flood tide samples. The most common invertebrate, Palaemonetes pugio, was taken in large quantities only in late afternoon-night flood tide samples. Three diversity indices were computed for each sample. Values for all indices varied widely between successive samples. The results emphasize a high degree of utilization of the intertidal creek habitat by larval and juvenile fishes. The diurnal-nocturnal activity patterns of some species, and the wide variation in catch size of the other species can permit use of the intertidal salt marsh habitat with reduced competition for available space and energy.
1. This paper tests the possibility that, primarily through their effect on invertebrate prey densities, sediment characteristics can be used to predict the densities of shorebirds (Charadrii), on the inner banks of the Wash, east England. 192 quadrats were established with, on most shores, a transect of nine quadrats from the marsh edge to the Low Water Mark (LWM). Shorebirds were counted in winter in each quadrat. The densities of the main invertebrate prey species were sampled in early winter/late autumn at the mid-point of each quadrat, together with the sediment particle size and organic content. The time for which each quadrat was inundated over high water spring tides was also measured. 2. Regression analyses revealed that the densities of each of the eight shorebird species were related to the densities of several of their known, or suspected, prey species. A similar analysis showed that the densities of most prey species were, in turn, related to the proportion of one or more of the four sediment particle size categories in the substrate; coarse sand, fine sand; silt and clay. The densities of most invertebrates were also related to inundation time, with most relationships being strongly non-linear. 3. In most cases, the effect of prey density on bird density remained significant when the sediment characteristics and inundation time, together with a measure of a quadrat's distance from the LWM, were added to the regression analysis of variations in bird densities. In a few cases, one component of the sediment particle size distribution additionally affected bird density. On the west and south-west sides of the Wash in particular, the densities of several shorebirds were also markedly higher in quadrats close to the LWM, even with the effect of both prey density and sediment particle size taken into account. The results were largely consistent, however, with the hypothesis that the main factors determining spatial variations in bird densities were variations in prey densities. 4. It was concluded that, because of the strong influence of the sediment on the densities of most prey species, and because the model was based on transects which spanned the whole width of the shore so that the tidal inundation time was comparable in each, the sediment particle size distribution could be used to predict shorebird densities directly. It was not necessary first to predict the densities of the invertebrates on which they feed.