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).