Spatio-Temporal Variation Patterns of Bird Community in the Oasis Ecosystem of the North of Algerian Sahara

The spatial and temporal variation patterns of birds were investigated in the Oasis ecosystem of the North of Algeria Sahara. This contribution aimed to investigate the poorly studied bird fauna of Bousaâda oasis. The direct observation method was used for bird counts, adopted only during the breeding period. A total of 53 species of birds from 29 families and 16 orders were assessed in the different habitats of the Oasis (palm, fruit trees and, cultivated crops). The Passeriformes order was the most abundant represented by 35 species and 16 families. The relative abundance and species richness were recorded during our study period over different seasons and thought that whole surveyed stations represent all the oasis habitats. The Boussaâda oasis holds 18 resident-breeder species and is a transit zone for many migratory birds 14 and 10 species for summer and winter migrants respectively) and11 occasional visitor ones. These results confirmed the positive effects of stations and seasons on the richness and abundance of birds of Bousaâda oasis.


INTRODUCTION
Biodiversity studies attracted the world's attention to ensure several ecosystem services and its impacts on humans (Harrington et al., 2010). Declines in biological diversity during the 20th century have been directly attributed to the growing human activities (Heywood and Watson, 1995). The oasis is considered as a fragile ecosystem of the arid climate. Its landscape relies mainly on the structure of desert-oasis-river components (Yang et al., 2010). Over the centuries, oases have played a key role in the local socioeconomic development and in the ensuring of ecological balance. Over the last century, the oasis ecosystem has been affected seriously due to multiple natural and human constraints: drought, salinity, urbanization, and layout programs (Botes and Zaid, 2002).
Oases constitute key habitats due to their ecological characteristics to survey biodiversity (Chenchouni, 2012). According to the Ramsar Convention, oases are considered a type of inland wetlands (Ramsar, 2007). However, the ecological characteristics of oases in Algeria varied between regions following their geographic location. Although, the ecosystems of arid and desert regions has very peculiar biodiversity related to locale biotope and climate (McGinley, 2007) particularly birds (Roshier et al., 2001;Mwaura, 2010;Chenchouni, 2012).
The avifauna of Algerian oases were reported by Heim de  and Dupuy (1966) followed by updated data (Ledant et al., 1981;Isenmann and Moali, 2000;Samraoui, 2008). In southern Tunisia, many surveys were undertaken on the diversity and distribution of this avifauna (Selmi et al.,2002).Some studies were available on birds of oases in Algeria (Boukhemza, 1990;Chenchouni, 2012;Bensaci et al., 2013) but these are insufficient and limited to some regions and/or occasional observations. The present study was undertaken with the two basic objectives: i) to assess the bird diversity of the oasis located in arid climate differently to previous studies on Oases of Sahara Desert; and ii) to evaluate the spatiotemporal variation patterns of birds within Bousâada oasis.

Study Area
Bousâada (35° 12' 36.97" o N, 4° 10' 46.08" o E) is a marvelous oasis, located in the centre of the northwardly located state of Algeria at an altitude of 602m above the sea level (Figure1). The oasis is delimited by three structural groups: high plains of the Algiers-Oran steppes to the north and east, Saharan desert to the south, and Saharan Atlas to the west (Kaabeche, 1990). The area has an arid climate (annual mean temperature 25°C, average annual precipitation <185.8 mm) with dry season extends all along the year. Bousâada oasis is the first one encountered while heading from the coastline to the Sahara Desert (Boutabba, 2013) Oasis is crossed by Oued Bousâada, flowing at the foot of a huge cliff used for irrigation. The landscape is dominated by palm trees (Phoenix dactylifera L.) mixed with fruit trees and cultivated crops.

Bird Surveys
Bird surveys were conducted from March 2019 to March 2020 which covered all seasons of the year, with three passes are performed in each station during each season, which normally can detect all wintering, visitor passage and breeding species (Blondel, 1975).The territorymapping method is considered the most accurate and appropriate method for estimating species richness and then the abundance of avian communities, particularly in open habitats (Bibby et al., 1992).
This approach based on the assessment of all contacted birds and their abundances during a period of 15 minutes. A pair of binoculars (8×42) and a field guide book were also used to identify the species of birds observed. Counts were performed in calm weather, avoiding harsh weather, wind and bitter cold). A total set of 19 census points (station) was allocated non-randomly, based on accessibility and habitat type. Overall, these stations located in four (4) studied regions: Zakat El-Kib (ZEK), Loulaj (LLJ), JnanLebtom 1 (JB1) and, JnanLebtom 2 (JB2) ( Table 1). These regions have different habitat characteristics. Depending on their location, the surveyed stations are the subject of varied urban pressure and human disturbance. Phenological types used were (1) resident breeder (RB) species present all year with breeding proof; (2) winter visitor (WV) species observed exclusively during the rainy season; (3) summer visitor (SV) migratory species in summer; (4) occasional visitor (OV) species that observed in the study region at least once (Isenmann and Moali, 2000).
Avian species richness was defined as the total number of species detected at each station during the study period. However, the species abundance

Data Analysis
Statistical tests were performed using SPSS 17.0 with a significance level of P ≤0.05. All means are shown ± standard error of mean unless stated otherwise.
We used parametric tests and ANOVA to test all variables,when the normality (Kolmogorov-Smirnov test) and homoscedasticity (Levene test), variables that did not conform to the requirements for parametric tests were transformed by logarithm or a square-root transformation before all analyses (Underwood, 1996).
A one-way multivariate analysis of variance (MANOVA) was performed to test the effect of stations and seasons on therichness and abundance of assessed birds.
The Shannon's diversity index ( '=−∑ log ), where : is the proportion of individuals belonging to the : the species) was used to identify thediversity of bird species in different stations (Magurran, 2004). High values of H' and low values of H' indicate high species diversity (Krebs, 1999). Equitability (Evenness), the distribution of abundances among species was computed as J'= H'/lnS, whereas S is the number of species in each station (Magurran, 2004). Evenness ranges from 0 to 1 and as it approaches 1, individuals are partitioned equally among species (Krebs, 1999).

Specific Richness
A total of 53 bird species, representing 40 genera, 29 families and 16 orders were recorded in the Oasis of Boussaâda from all surveyed stations (Table 1). Order Passeriformes was represented by the highest number of species (35; 16 families). Order Columbiformes was represented by 4 species while orders Accipitriformes, Pelecaniformes and Charadriiformes by two species each. Other orders (11) were represented by only a single species, (Table 2).

Shannon-Weaver Diversity and Evenness (Equitability) Indexes
The highest value of the Shannon diversity index was observed in the JB1-3 (3.64) and the lower of 2.34 was recorded in the JB1-4 station (Fig 2). The maximum value of the equitability index was recorded in the LLJ5 station (0.77), where the minimum value was noted in the JB1-4 (0.53) (Figure 3).

DISCUSSION
The inventory of birds in Bousaâda oasis suggests that 53 bird species, representing 7.66% of the Algerian birds (Isenman and Moali, 2000). However, in the Ziban region (Biskra, Algeria) Farhi and Belhamra (2012) identified 136 species representing 18 orders and 42 families (including waterbirds), of which Passeriformes were represented by 58 species (12 families). Guezoul et al (2013) reported 59 species present over alarger area,covering three oases of the Northern Algerian Sahara.
The highest richness of oases birds in Algeria was recorded in Timimoun region (SWAlgeria), where 100 species (59 genera, 28 families and, 12 orders) were described. Large number of species can be attributed to varied habitat sampled, such as oases, salt lake, reeds, and suburban area (Boukhemza, 1990).
Order Passeriformes is prominently represented in all avian populations that are present in the oasis (66% of assessed species). This is in line with previous studies on oases birds of Algeria (Farhi and Belhamra, 2012;Guezoul et al., 2013). The presence of several bird species in the surveyed oases is closely linked to their phenology.
During the monitoring many species were presented in the most surveyed stations such as :Hybrid sparrow, Collared Dove, Laughing Dove, Turtle Dove, Rock Dove, Greenfinch and Blackbird), some of these are known to have an expansion of their distribution range over the Mediterranean basin (Bergier et al., 1999;Bendjoudi et al., 2013) and worldwide (Bonter et al., 2010). These species are considered as the most abundant and the common birds in all oases of the Tunisian Sahara (Selmi., 2002).
Bousaâda oasis is known to have a high anthropogenic pressure (urbanization, high rate of ground water extraction, land encroachment) which led to the loss of many habitats, affecting bird's richness and abundance. Donnelly and Marzluff (2006) confirmed that bird species richness decreases with increasing urban land cover.
Abundance of some species, such as feral pigeons, swallows, swifts, and a few other species that breed in walls indicated increased urbanization. Thus, landscape transformation of the oasis during last decade has been indicated previously (Botes and Zaid, 2002;Meddich et al., 2018).Significant special variation reveals the high quality of habitats with high supply of seeds and productivity (Emlen, 1974).
The stations presented a high urban pressure and human disturbance were recorded a low species richness, which is in confirmation of Chace and Walsh (2006) and Sandström et al., (2006). Furthermore, variations in the composition of bird communities and abundances of species tend to be associated with the composition and structure of vegetation (Sewell and Catterall, 1998;White et al., 2005 andDaniels andKirkpatrick, 2006).
Shannon and Weaver's index allow us to measure the complexity of a stand. A high value of this index indicates a settlement in many species for a small number of individuals. Conversely, a low value of the latter is either or a settlement characterized by a small number of species for many people, or to a settlement in which there is a dominant species. In other words, he studied the equilibrium of populations in an ecosystem.
Despite the rapid urbanization of Bousaâda region, this relevant diversity can be used to support the conservation of native bird populations, which is particularly important in biodiversity hotspots located in the arid region.

CONCLUSION
Our results confirmed that Bousaâda oasis represents an important habitat exploited as wintering grounds, stopover site during trans-Saharan migration, and breeding sites for several species.
Regarding the strategic geographic situation of this region as a key in the regional scale biodiversity and bird's dynamic this needs further investigations on habitat preferences of birds.  (1990). Contribution a` l'étude de l'avifaune de la région de Timimoun (Gourara) :