Taxonomic Richness
Avian fauna associated with limnetic aquatic ecosystem, waterbirds, from 35 reservoirs of varying age is presented in Table 1. A total (γ-diversity) of 85 bird species from 54 genera, 25 families and 15 bird orders were recorded during the study period (Tables 1 and 2). When the seven species that are not listed as waterbirds in a strict sense, by ornithologists, are excluded the total ornithological richness of waterbirds of the surveyed reservoirs (γ-diversity) is 78 species from 48 genera, 22 families and 11 orders. Most of the waterbirds (60%) recorded are all-year residents and 4.71% (n=4 bird species) are intra-African migrants and visitors. Thirty of the waterbirds (35.29%) recorded are Palaearctic migrants/winter visitors (see Appendix S3 in supporting information). Out of the total bird species recorded five of species: Black-Tailed Godwit (Limosa limosa), Ferruginous Duck (Aythya nyroca ), Lesser Flamingo (Phoeniconaias minor),Maccoa Duck (Oxyura maccoa) and Pallid Harrier (Circus macrourus) fall under the near threatened (NT) IUCN conservation status designations. Two species: Hooded Vulture (Necrosyrtes monachus ) and Common Pochard (Aythya ferina ) fall under critically endangered (CR) and vulnerable (VU) conservation status designations, respectively. While the rest (91.8%) birds recorded are of least concern (LC) under the IUCN conservation status designations (Table 2).
Charadriiformes had the highest number of recorded taxa (7 families, 15 genera, 27 species) followed by Pelecaniformes (4 families, 9 genera, 15 species) (Tables 1 and 2). Within the recorded Charadriiformes, the Scolopacidae (Sandpipers and allies) was the most widespread family of that order (12 species). Of all the families recorded, Anatidae (order: Anseriformes) was the family with the most recorded genera (7 genera; 15 species; including geese, ducks, teals), followed by the Scolopacidae (order: Charadriiformes) (6 genera; 12 species; including sandpipers and snipes). The Ardeidae (herons and egrets), Ciconiidae (storks) and Accipitridae (raptors) were the next in number of families recoded with 8, 7 and 5 species per family, in that respective order (Fig. 3).
The alpha (α) diversity of reservoirs varies from 3 to 32 with 14.23±6.72 (mean ± standard deviation) birds per reservoir. Mai Nigus (n= 32 species) and Tsinkanet (n= 26 species) had the highest bird species recorded, followed by Mai Gassa I reservoir (n= 23 species) and Haiba reservoir (22 species) (Fig. 4A). Two spatial distribution pattern of species richness (α- diversity) of waterbird population are clearly detected. The first pattern is within Northern cluster where the central reservoirs have a higher alpha diversity while northern reservoirs have relatively lower alpha diversity when plotted along the geographic location of reservoirs (Fig. 4B). The second pattern is within the southern Tigray where higher alpha diversity is observed in the center while reservoirs in the peripheries have lower alpha diversity (Fig. 4B). The second pattern becomes clearly visible after removing Haiba reservoir from the data set which is connected to Meala reservoir.
Frequency of occupancy of the reservoirs varies from 1 to 35 birds (Table 2). From the 35 reservoirs sampled, the highest frequency of occupancy have been recorded for Egyptian Goose (Alopochen aegyptiaca ) followed by: Common Sandpiper (Actitis hypoleucos ) and Grey Heron (Ardea cinerea ) recorded from 28 and 26 reservoirs, respectively (Table 2 and see Appendix S3 in supporting information). Three of the Near-threatened birds recorded in this study were from a single reservoir while the two other birds in this category status: Ferruginous Duck (Aythya nyroca ) and Maccoa Duck (Oxyura maccoa ) are recorded from two and five reservoirs, respectively (Table 2). The spatial distribution of the two endemic species recorded was also different. The Wattled Ibis (Bostrychia carunculata) is recorded from nine reservoirs whereas Spot-breasted Lapwing (Vanellus melanocephalus ) is recorded from Mai Nigus reservoir only (Table 2 and see Appendix S3 in supporting information). The spatial distribution of the four intra-African migrants recorded: African Openbill (Anastomus lamelligerus ), Southern Pochard (Netta erythrophthalma ), Abdim’s Stork (Ciconia abdimii ) and Pied Avocet (Recurvirostra avosetta ) did not show a uniform pattern. The first two species were recorded from a single reservoir each while Abdim’s Stork and Pied Avocet were recorded from seven and three reservoirs, respectively (Table 2 and see Appendix S3 in supporting information).