CC BY
29Cl RUSSIAN JOURNAL OF ECOSYSTEM ECOLOGY Vol. 7 (l), 2022
Reœived 05.01.2022 Revised 26.02.2022 Accepted 10.03.2022 ^^^^ESEARCHARTÎCL^^ Open Access
DOI 10.21685/2500-0578-2022-1-4
SEASONAL VARIATION IN SPECIES RICHNESS AND ABUNDANCE OF WATERBIRDS IN THE SUBURBS OF ASMARA CITY, ERITREA
R. T. Tewelde1, D. B. Araya2
1 Eritrea Institute of Technology, P.O.Box 12676, Asmara-Eritrea
2 Private naturalist, P.O.Box 5368, Asmara-Eritrea
1 teweledert@gmail.com,2 dawitray1@gmail.com
Abstract. Wetlands provide organisms with a diverse range of breeding sites and food, allowing them to survive during the non-breeding season. Despite the hotspot area, the waterbird fauna in the suburbs of Asmara city is poorly described. Information on the seasonal variation in species diversity and abundance is generally patchy. The study described the seasonal change in waterbird species diversity and abundance in different locations with varying physiological and ecological conditions. Waterbirds usually congregate around open wetlands, hence their abundance is more appropriately determined by counting all individuals in the congregate. The direct total area count method was implemented, and data was collected both during the dry (January-March) and wet (July-September) seasons of the year 2020. Species similarity between the study sites was calculated using The Morisi-ta-Horn index (CMH). A total of 5641 waterbirds were counted, representing 12 families and 47 species. The study shows a significant difference (p<0.05) in species abundance between the wet and dry seasons, although species richness is not statistically significant. The highest site similarity and low complementarity was seen between Radar and Adi-Nefas areas (CMH = 0.759). Despite seasonal species turnover, the total species diversity does not show significant change, while their abundance being notably higher during the dry season. Few waterbird species appear in dominant number, while the majority species are represented by a few individuals. In general, site similarity was high in the dry season, and maximum similarity was seen between Radar and Adi-Nefas sites both in the wet and dry seasons.
Keywords: wetland habitats, waterbirds, species composition, species richness, species abundance
Acknowledgement. The Rufford Small Grant Foundation funded the project, which the authors gratefully acknowledge. IDEA WILD also donated field equipment, which we appreciate. Finally, we thank the Department of Biology, Eritrea Institute of Technology, for their unwavering material and moral support.
For citation: Tewelde R.T., Araya D.B. Seasonal variation in species richness and abundance of waterbirds in the suburbs of Asmara city, Eritrea. Russian Journal of Ecosystem Ecology. 2022,7(1). Available from: https://doi.org/ 10.21685/2500-0578-2022-1-4
УДК 574.22
СЕЗОННЫЕ ИЗМЕНЕНИЯ ВИДОВОГО БОГАТСТВА И ЧИСЛЕННОСТИ ВОДОПЛАВАЮЩИХ ПТИЦ В ПРИГОРОДАХ ГОРОДА АСМЭРА , ЭРИТРЕЯ
Р. Т. Тевельде1, Д. Б. Арайя2
1 Технологический институт Эритреи, а/я 12676, Асмэра-Эритрея
2 Частный натуралист, а/я 5368, Асмэра-Эритрея 1 teweledert@gmail.com,2 dawitray1@gmail.com
Аннотация. Водно-болотные угодья предоставляют организмам разнообразные места для размножения и пищу, что позволяет им выживать в негнездовой сезон. Несмотря на горячую точку, фауна водоплавающих птиц пригородов города Асмэра описана слабо. Информация о сезонных изменениях видового разнообразия и численности, как правило, разрозненна. В данном исследовании описаны сезонные изменения видового разнообразия и численности водоплавающих птиц на различных участках с разными физиологическими и экологическими условиями. Водные птицы обычно собираются вокруг открытых водно-болотных угодий,
© Tewelde R.T., Araya D.B. 2022 Данная статья доступна по условиям всемирной лицензии Creative Commons Attribution 4.0 Page 1 from 8
International License (http://creativecommons.org/licenses/by/4.Q/), которая дает разрешение на неограниченное использование, копирование на любые носители при условии указания авторства, источника и ссылки на лицензию Creative Commons, а также изменений, если таковые имеют место.
поэтому их численность правильнее определять путем подсчета всех особей в скоплении. Был применен метод прямого подсчета общей площади, и данные собирались как в сухой (январь-март), так и во влажный (июль-сентябрь) сезоны 2020 г. Индекс Морисита-Хорна (CMH) использовался для расчета видового сходства между исследуемыми участками. Всего была учтена 5641 водоплавающая птица, представляющая 12 семейств и 47 видов. Исследование показывает значительную разницу (p<0,05) в обилии видов между влажным и сухим сезонами, хотя видовое богатство статистически не значимо. Наибольшее сходство участков и низкая комплементарность наблюдалась между районами Радар и Ади-Нефас (CMH = 0,759). Несмотря на сезонный оборот видов, общее видовое разнообразие не показывает значительных изменений, в то время как их обилие заметно выше в сухой сезон. Лишь немногие виды водных птиц преобладают по численности, в то время как большинство видов представлено несколькими особями. В целом сходство участков было высоким в сухой сезон, а максимальное сходство наблюдалось между участками Радар и Ади-Нефас как во влажный, так и в сухой сезон.
Ключевые слова: водно-болотные местообитания, водоплавающие птицы, видовой состав, видовое богатство, видовое изобилие
Благодарности. Авторы выражают признательность Фонду малых грантов Руффорда (Rufford Small Grant Foundation) за финансирование проекта. Авторы также высоко ценят роль организации IDEA WILD в безвозмездной передаче полевого оборудования. Авторы благодарят кафедру «Биология» Технологического института Эритреи за неизменную материальную и моральную поддержку.
Для цитирования: Тевельде Р. Т., Арайя Д. Б. Сезонные изменения видового богатства и численности водоплавающих птиц в пригородах города Асмэра, Эритрея // Russian Journal of Ecosystem Ecology. 2022. Vol. 7 (1). https://doi.org/10.21685/2500-0578-2022-1-4
Understanding the spatial and temporal patterns in species richness and their relative abundance is a fundamental challenge in ecology [1]. Studies show that climate [2, 3] and habitat productivity [4, 5] determine the structure of species assemblages, distribution, and abundance across large spatial scales. Temporal changes in climatic conditions can occur locally, resulting in climatic variability [6] and fluctuations in resource availability [7].
Seasonality affects the availability of food and cover for bird populations, which in turn affects the breeding success and, ultimately, the survival of the bird species [8]. Seasonal variations in the amount of rainfall and temperature as well as spatial and temporal microhabitat conditions are known to influence the availability of various food items for birds [9, 10]. Moreover, the seasonal weather variations can change water quality parameters in an area which in turn will change habitat variables, such as vegetation. Changes in vegetation characteristics affect the availability of important food resources [11, 12] to waterbirds which ultimately affects their diversity and abundance.
Despite the presence of a diverse range of wetland ecosystems across the country, no comprehensive studies have been conducted [3]. In Eritrea, there have been no significant scientific investigations on the ecology, diversity, or abundance of waterbirds. Waterbird diversity, abundance and seasonal dynamics are all poorly understood. This study looked at how waterbird species richness and abundance varied with seasonality in the suburbs of Asmara city.
Generally, dry season (November to April) and wet season (May to October) exist in the ecologi-
cal zone of Eritrea [13, 14]. According to Behrouzi-Rad [15], species diversity and abundance of waterbirds generally decrease in the dry season, where the level of the water body falls and/or dries up completely, as compared to the wet season. The annual migration of birds in response to seasonal changes is known to affect the species richness, their diversity, and abundance. Rajashe-kara and Venkatesha [16], however, reported relatively high number of waterbird species during the dry season, owing to the arrival of migratory birds in route to their breeding or wintering grounds.
The ability to prioritize and implement conservation initiatives requires accurate information on their population status, distribution range, annual cycle, and population change over time [17]. Waterbirds require a network of high-quality sites for nesting, refueling during migration, and surviving the non-breeding season [18], where this research emphasizes the importance of the site for water-birds during their annual cycle.
Material and methods
The research site is located in the central highlands at an elevation of 2325 m above sea level. It includes all the suburbs of the capital city Asmara, characterized by natural and manmade wetland habitats (seasonal natural surface water bodies, small to large-sized dams, and the sewage system of the city), irrigated farmlands, and open grazing areas. Rainfall is generally inadequate and unreliable with annual rainfall 500 mm [14]. Moreover, it includes wetlands proposed important bird areas, which are known to support regionally and globally threatened birds throughout the year.
Based on the water holding capacity and vegetation complexity, the study area has been stratified into three district study units (Sembel, Radar, and Adi-Nefas areas). Sembel is characterized by rich vegetation cover and floating aquatic weeds surrounded by trees and shrubs. Used for small-scale irrigation farms. Radar includes several small dams and the sewage stream of Asmara City along with the irrigation farmlands and open grazing areas. The Adi-Nefas area features an open dam with no floating vegetation used for animal watering and irrigation.
Prior to the actual survey, spots were predefined purposively at intervals. The site was covered systematically traversing on foot giving general thought to the light conditions. Multiple counts were made both during wet and dry seasons. The relative abundance of each species seen or heard was estimated(counted whenever possible) for each study unit, based on the assumption that common birds are more likely to be seen first, using the whole area search technique.
Birds in flight were not counted to reduce the incidence of double counting [19]. Counting was performed using a 10 x 50 binocular. The research was conducted from January to March (dry season) and July to September 2019 (wet season). Each study site was surveyed twice a month for a total of 12 times. Waterbirds were counted during the early morning (6-10) and late afternoon (16-18) hours when they are most active. Birds of Ethiopia and Eritrea: an atlas of distribution [20] and Birds of the Horn of Africa: Ethiopia, Eritrea, Djibouti, Somalia, and Socotra [21] were used to identify birds.
The total bird count was generated for each study site/unite and the relative abundance (R) of each species was calculated. Species similarities between the three sites was estimated using the quantitative Morisita-Horn index (CMH), although it is a little biased on the difference in species richness and sample size [22]. The value of the similarity indices ranges between zero, no species overlap, and one, complete similarity. Generally, CMH > 0.5 is rated as a high similarity, while CMH > 0.75 is a very high similarity. MannWhitney U test, a non-parametric test, was used to determine the significance of waterbird abundance at the various study sites between the wet and dry seasons; and Kruskal-Wallis to test the significant level abundance among the three study sites.
Results and discussion
Species richness
Overall, 47 species of waterbirds belonging to five orders and 12 families were identified. There were 37 species encountered during the wet season, with 13 species common to all sites, compared to 33 species during the dry season (Table 1 and 2). During the dry season, 15 species were identified across all sites. Thus, there is no statistically significant difference in species richness in the wet and dry seasons. As well during the wet and dry seasons, 23 resident species were recognized. Similarly, 14 species were only found during the rainy season, whereas 10 were discovered exclusively during the dry season.
Table 1
Species diversity and relative abundance of waterbirds during the wet season
Scientific Name Radar Adi-Nefas Sembel Total R*
1 2 3 4 5 6
Ciconia abdimii 46 - 23 69 3.1
Mycteria ibis - 2 - 2 0.1
Ardea melanocephala 21 2 5 28 1.3
Ardea cinerea 12 1 - 13 0.6
Ardeola ralloides - - 5 5 0.2
Vanellus tectus 37 8 17 62 2.8
Vanellus spinosus 94 3 25 122 5.5
Charadrius tricollaris 10 7 - 17 0.8
Charadrius hiaticula 1 - - 1 0.0
Vanellus senegallus - - 6 6 0.3
Tringa ochropus 56 2 1 59 2.7
Actitis hypoleucos 36 - 3 39 1.8
Alopochen aegyptiaca 203 271 52 526 23.8
Oxyura maccoa 3 - 6 9 0.4
Spatula querquedula - - 5 5 0.2
Anas acuta 19 1 237 257 11.6
Fulica cristata 3 108 92 203 9.2
Fulica atra 47 - - 47 2.1
Threskiornis aethiopicus 172 1 3 176 8.0
Bostrychia carunculata 39 6 45 2.0
Plegadis falcinellus - - 4 4 0.2
End of the Table 1
1 2 3 4 5 6
Bostrychia hagedash 27 - 14 41 1.9
Chlidonias leucopterus 3 - - 3 0.1
Gelochelidon nilotica 1 - - 1 0.0
Bubulcus ibis 17 9 3 29 1.3
Ardea intermedia 48 - 5 53 2.4
Egretta garzetta 41 - - 41 1.9
Spatula clypeata 33 - - 33 1.5
Limosa limosa 1 - - 1 0.0
Pelecanus rufescens - 23 - 23 1.0
Scopus umbretta 23 2 4 29 1.3
Tachybaptus ruficollis 26 30 28 84 3.8
Anas crecca - - 6 6 0.3
Himantopus himantopus 22 - 15 37 1.7
Rougetius rougetii 3 7 4 14 0.6
Tringa totanus - - 16 16 0.7
Calidris pugnax 75 6 26 107 4.8
Total Individuals 1119 483 611 2213 100
Total Species 29 17 26 37
R* = Relative Abundance.
Table 2
Species diversity and relative abundance of waterbirds during the dry season
Scientific Name Radar Adi-Nefas Sembel Total R
Egretta garzetta 43 35 32 110 3.2
Podiceps cristatus 27 20 17 64 1.9
Pelecanus rufescens 124 87 - 211 6.2
Ardea cinerea 22 18 11 51 1.5
Ardeola ralloides - - 15 15 0.4
Ardea goliath 8 - 6 14 0.4
Egretta garzetta 19 7 53 79 2.3
Bubulcus ibis 13 5 9 27 0.8
Ciconia abdimii 23 12 - 35 1.0
Ciconia nigra 6 8 - 14 0.4
Ciconia ciconia 9 - - 9 0.3
Mycteria ibis 12 2 - 14 0.4
Threskiornis aethiopicus 83 - 26 109 3.2
Plegadis falcinellus - - 37 37 1.1
Scopus umbretta 18 7 - 25 0.7
Alopochen aegyptiaca 273 535 147 955 27.9
Spatula clypeata 98 143 139 380 11.1
Fulica cristata 92 59 7 158 4.6
Vanellus spinosus 82 63 49 194 5.7
Charadrius tricollaris 14 6 36 56 1.6
Charadrius dubius 21 39 11 71 2.1
Limosa limosa - - 73 73 2.1
Tringa stagnatilis 10 59 18 87 2.5
Actitis hypoleucos 16 26 11 53 1.5
Tringa ochropus - - 74 74 2.2
Calidris minuta 4 28 - 32 0.9
Himantopus himantopus 15 7 27 49 1.4
Himantopus mexicanus - 13 2 15 0.4
Gallinago media - 1 - 1 0.0
Calidris pugnax 12 184 68 264 7.7
Anas acuta - - 125 125 3.6
Anas sparsa - - 5 5 0.1
Oxyura maccoa 13 - 9 22 0.6
Total Individuals 1057 1364 1007 3428 100
Total Species 25 23 25 33
During the wet season, both Radar and Sembel areas scored the highest number of species, 29 and 26 species respectively; while 17 species were encountered in Adi-Nefas. During the dry season, in contrast, all three sites scored a similar number of species, both Radar and Sembel with 25 species followed by Adi-Nefas (23). Both Radar and Sem-bel exhibit a slight decrease in species richness during the dry season, whereas Adi-Nefas exhibits more than a 35 % increase in the number of species when compared to the wet season.
The highest number of shared species (20) occurred between Radar and Sembel sites, in the wet season, followed by Radar and Adi-Nefas (15);
whiles 21 species were common to Radar and Adi-Nefas areas in the dry season. Overall, the quantitative Morisita-Horn index (CMH) shows the highest similarity and low complementarity between Radar and Adi-Nefas areas (CMH = 0.759). In contrast, Adi-Nefas and Sembel scored the lowest index (CMH = 0.484) (Table 3) indicating relatively low similarity between the sites. This is mainly due to the topographic and productivity difference between the sites during the various seasons. Generally, the similarity between the sites is high or very high during the dry season compared to the wet season.
Table 3
Species similarity among the four study sites in Mole National Park, as shown by the quantitative Morisita-Horn index (CMH)
Wet-Season Dry-Season Total Similarity
Adi-Nefas Sembel Adi-Nefas Sembel Adi-Nefas Sembel
Radar 0.468 0.257 0.844 0.632 0.759 0.568
Adi-Nefas 0.308 0.621 0.484
Species abundance
Generally, 2213 waterbirds were counted during the wet season compared to 3428 in the dry season, which shows a significant difference in the abundance of waterbirds between the two seasons (see Table 1 and 2). According to [23], waterbirds gather around the permanent water bodies, and often seen the high numbers of individuals, during the dry season. The mean abundance of waterbirds in the dry season is statistically significant (P< 0.05) compared to the wet season recording the highest number of individuals in both Adi-Nefas and Sembel, while there is no significant difference in Radar.
Only 12 species were represented by >100 individuals, whereas 23 species occurred in small
numbers ((<50) during the study period, 9 species of which were represented by less than 10 individuals (see Table 1 and 2). Generally, only a few species appeared in dominant number, while the majority species (Fig. 1) represented by a few individuals. The trend with a few common species and many species represented by few individuals seemed not to be strongly influenced by species turnover. Species turnover was observed in all of the study sites over the study period. As a result, some species moved in and others moved out of the site. This might mean that migratory birds, such as waders, are either using the sites as stopover locations, to refuel during the long journey, or wintering ground to overcome drought and avoid competition in their breeding area.
Egyptian Goose Alopochen aegyptiaca was the most abundant species during both wet (R = 23.8) and dry (R = 27.9) seasons, followed by the Northern pintail Anas acuta (R = 11.6), and Northern Shoveler Spatula clypeata (R = 11.1) respectively (Table 1 and 2). Similarly, Egyptian Goose was the most dominant species in Radar and Adi-Nefas
areas throughout the year. In the wet season, Northern pintail was found abundantly in Sembel (Fig. 2,a), and Egyptian Goose and Northern Shoveler, however, appeared to be equally dominating during the dry season (Fig. 2,b), likely due to high food productivity and low human disturbance.
<0 b) Fig. 2. Species rank order in the study units relative to the wet (a) and dry (b) seasons
Conclusion
The study shows the importance of the water-bodies to wetland species, including internationally threatened. In general, there is no discernible difference in species richness across seasons and study sites. High species turnover was observed between the wet and dry seasons, which coincided with bird migration. The abundance of waterbirds
shows significant variation between the seasons, with high abundance counted in the dry season. Only a few waterbird species appear in dominant number, while majority species represented by a few individuals. Generally, the site similarity is high during the dry season of the year, and the highest similarity scored between Radar and Adi-Nefas sites both in wet and dry seasons.
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