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Ukrainian Journal of Ecology
Ukrainian Journal of Ecology, 2018, 8(4), 41-45
ORIGINAL ARTICLE
Aquatic bird assemblages of a tropical African man-made lake
M.M. Keke, A.O. Elizabeth
Department of Zoology, University of Ilorin, Ilorin, Nigeria E-mail: [email protected] Received: 10.10.2018. Accepted: 09.11.2018
Aquatic birds are important biotic components of Lake Ecosystem serving as indicator of pollution, sources of protein, fishing agent, income, recreation, tourism, sport and pest control. The aim of this study was to provide a baseline data and checklist of the bird assemblages in Asa Lake, Ilorin, Nigeria. Bird sampling was conducted weekly for 24 weeks, by walking 10 mS-1 along a line transect on the bank of the lake. The populations were classified as rare, frequently seen and common based on the number of sightings, and abundance. Diversity indices such as dominance, evenness, Simpson diversity, Shanon-Weiner diversity, Marglef's richness were estimated. 13682 birds consisting of 17 species in 9 families were recorded in the lake. Species were found in highest number during the rains. Water fowl was the most abundant species 42.21%. African jacana was the least abundant constituting 0.67%. Family Ardeidae was the most abundant in terms of species diversity. Three species were commonly seen, four frequently seen, while nine were rare. Diversity indices of the bird species were; (D) 0.045, (1-D) 0.95; (eAH/S) 0.96, Margalef richness 3.67 and (H) 2.99. The assemblage of bird species in the lake was high due to the availability of food, submerged aquatic macrophytes seeds and foliage, large volume of water, surface area and depth of the lake and absence of large predators. Morphological characteristics and behavioural tactics of the birds were attributed to the high occurrence of some of the birds. For continued residency of the birds in the lake, lake best management practices (LBMP) should be implemented. Continuous monitoring of the birds (bio monitor) in the lake should also be done to give an insight into the ecological conditions of the lake and at the same time serving as aesthetic organisms in the lake. Keywords: Birds; assemblages; lake; foraging; diversity; macrophytes; waterfowl
Introduction
According to Hoyer (2013), aquatic birds are birds that live at least part of their lives in or around water. Lakes serve as excellent resting/wintering, breeding/nesting, and feeding habitat for birds. Aquatic birds are very significant to any aquatic environment, their presence or absence may indicate the ecological conditions of such environment (Rajpar and Zakaria, 2011). Their presence plays a crucial role in the limnology, aesthetic value and food chain of lakes, while their absence or low assemblage could indicate limnological imbalance, pollution, habitat loss and degradation, thus serving as lakes and reservoirs biological indicators.
Species composition, abundance and diversity of aquatic birds in a lake depend on availability of food, foraging behaviour, surface area, trophic status, productivity, aquatic macrophytes richness and limnological characteristics, morphometrics of the lake. Bird assemblage in a lake could be used in water quality assessment, index of pollution, avifauna biodiversity conservation and lake management. Apart from these, aquatic birds of lakes could serve as sources of protein (meat), fishing agent (cormorant fishing), income, recreation, tourism, sport, and pest control.
There are numerous lakes and reservoirs in Africa created for different purposes (Mustapha, 2011). But, very few studies have been done on their avifauna composition, diversity, distribution and abundance. The aim of this study was to document the species composition, diversity and abundance of aquatic birds of an important tropical African lake (Asa Lake) in Nigeria. This is with a view to providing a checklist of the bird assemblages and baseline data and information on the bird's species in the lake for their subsequent monitoring, utilization, sustainable exploitation, conservation and management.
Materials and methods
Study site description
Asa Lake was constructed in 1977 primarily for domestic water supply to Ilorin town by the Kwara State Government of Nigeria. The lake is located at about 5 km south of Ilorin the Kwara State capital across river Asa at a latitude 08°26' north and a longitude 04°29'. The dam is 597 m in length and 27 m height with a crest width of 6 m (Table 1). Surface area of the reservoir is 302 hectares, and the reservoir is fed by four river tributaries with river Asa being the major river. The sampling sites extended from the dam site to Odore, Laduba and Afon basins. The periods of maximum water levels associated with
floods around the lake usually commenced as from June to middle of October corresponding with the rainy season starting from May to the early October (Araoye, 2009).
Table 1. Morphometrics charcteristics of Asa Lake. Features Overall length Storage capacity
Extent of lake Earth Embankments: Length Crest width Maximum height Upstream slope Downstream slope Earth fills
Measurements
596 m
43 million cm3 18 km
402 m 6 m 27 m 0.04375 0.00072338 250,000 cm
3
Non-overflow concrete gravity section: Length Crest width Maximum height Spill way: Length Height
Maximum discharge Total volume of concrete:
130 m 6 m 11 m
65 m 14 m
79,000 cm3s
49,000 cm3
Source: Kwara State Utility Board, Ilorin.
Bird sampling/survey
The sampling was conducted weekly for 24 weeks between January and June 2016. Bird sampling was made by walking at a slow pace (about 10 m S-1) along the line transect made on the bank of the lake (Gaston 1975; Bibby et al., 2000). Birds were counted at their point of first detection and care was taken to ensure that same birds were not counted twice. Birds that were seen in or on the lake were the only ones censured. The number of aquatic birds of various species was recorded on each census day. The birds were identified to species level using field guide of Grimmet et al., (1999), Ali (1996), Grimmett & Inskipp (2007), Serle et al., (1977), Evans (1994), Shirihai & Christie (1996) and Harris et al., (1991). Call notes of the birds were sometimes used for identification after confirmation from the locals. Counting of the birds was made in the mornings between 07.00 and 10:00 am and/or in the evenings between 4:00 and 6:00 pm. Classification and occurrence of bird in population analysis
The bird populations were classified as rare (R), frequently seen (Fs) and common (C) based on the number of sightings, and abundance. Similarly, based on the percentage frequency of occurrence of the bird species, the scores were classified as 0.003.00% rare (Re), 3.01 -9.99% less common (Lc) and 10.00-100% common (Co). Data analysis
Dominance indices (D), Evenness (eAH/S), Simpson diversity index (1-D), Shanon-Weiner diversity (H), Marglef's richness indices and two-way ANOVA at P<0.05 were estimated using the computer program PAST version 3.20 software (Hammer et al., 2011). The percent abundance and percent frequency of bird species were also calculated. The diversity indices measured were according to Magurran (1988).
Results and discussion
Bird assemblages
A total of 17 species of aquatic birds in 9 families were recorded in the lake spanning 24 weeks of survey, covering both dry and rainy seasons (Table 2). All the species were found in the two seasons. A total number of 136832 birds were sighted in the lake in the two seasons with the rainy season having the highest number of 8928 (65%) of the total abundance of birds. All the species were also found in their highest number during the rainy season. There was significant difference at P<0.05 in the abundance of the species between the seasons, with rainy season abundance significantly higher (P<0.05) than the dry season. Water fowl of/and the family Anatide was the most abundant species and family in the lake in both dry and rainy seasons. It constituted 42.21% of the total number of birds found in the lake. African jacana of/and the family Jacanidae was the least abundant species constituting 0.67% of the total bird population in the lake. The family Ardeidae was the most abundant family in terms of species diversity with four species, while five families were represented by a single species (Table 2). Based on sighting and percentage frequency of occurrence, three species were commonly seen and recorded in
Ukrainian Journal of Ecology, 8(4), 2018
Ukrainian Journal of Ecology 43
population sampling and survey; four species were less common and frequently seen, while nine species were rare in terms of percentage occurrence and sighting on the lake (Table 3).
Table 2. Bird species composition and abundance of Asa Lake, Ilorin, Nigeria.
Seaso Wee GH BH PH WF FH AJ BL SL WL BK PK Py CE WD SP LD S Total
n k K
Dry 1 18 10 12 212 5 2 15 12 9 18 6 4 26 30 2 6 3 391
2 12 7 9 202 4 10 8 6 12 4 3 28 32 1 9 2 351
3 9 12 10 186 6 1 8 10 7 14 9 5 30 41 3 12 4 370
4 21 14 18 172 8 1 10 12 9 19 12 6 36 45 5 18 6 416
5 18 10 14 150 5 2 6 7 5 10 8 5 30 36 3 12 4 330
6 15 8 10 162 4 5 10 7 9 12 7 36 42 5 16 7 361
7 20 10 14 164 3 1 8 12 9 12 14 6 32 40 2 14 5 373
8 16 12 16 180 6 1 6 10 7 10 8 5 35 48 1 18 3 390
9 22 8 12 192 5 2 7 10 5 6 10 2 40 52 4 20 2 408
10 25 6 8 204 3 1 6 8 3 8 12 2 45 56 6 20 4 427
11 20 10 14 220 2 1 5 6 4 7 7 4 48 58 8 24 6 455
12 24 12 15 228 4 8 5 5 5 5 5 54 60 10 22 8 482
Total 22 11 15 227 55 12 94 11 76 13 10 54 440 540 50 19 54 4754
0 9 2 2 0 0 7 1
Rain 13 26 14 18 240 6 1 10 8 6 9 8 8 50 60 10 30 10 527
14 24 10 12 245 7 2 12 10 7 12 12 6 56 62 12 30 10 543
15 28 18 16 250 10 4 18 10 5 14 16 10 60 65 14 36 12 601
16 31 26 24 266 12 3 22 18 5 16 10 10 62 70 13 38 15 657
17 30 32 20 275 12 5 20 15 4 24 10 12 65 66 15 40 18 680
18 26 30 25 300 15 5 25 20 10 22 8 14 68 72 18 41 20 737
19 22 28 32 312 18 7 28 22 12 25 14 10 76 75 22 45 22 789
20 24 34 34 315 21 9 30 25 15 32 12 8 78 78 25 48 25 833
21 25 36 40 320 25 10 22 18 18 36 16 14 84 82 30 50 28 875
22 20 26 46 300 28 12 18 15 14 40 22 18 90 80 30 50 30 861
23 21 24 54 330 20 10 15 10 8 42 20 20 92 84 26 52 30 881
24 25 29 60 350 36 12 10 8 5 45 24 22 96 88 25 55 30 944
Total 30 30 38 350 21 80 23 17 10 31 17 152 877 882 24 51 25 8928
2 7 1 3 0 0 9 9 7 2 0 5 0
Overall Total 52 42 53 577 26 92 32 28 18 44 27 206 131 142 29 70 30 1368
2 6 3 5 5 4 9 5 7 9 7 2 0 6 4 2
Key: GH=Grey Heron; BH=Black Heron; PH=Purple Heron; WF=Waterfowl; FH=Fish Hawk; AJ=African Jacana; BL=Blackhead Lapwing; SL=Spur winged Lapwing; WP=Wattled Lapwing; BL=Blue breasted Kingfisher; PK=Pied Kingfisher; PyK=Pygmy Kingfisher; CE=Cattle Egret; WD=Whistling Duck; SP=SandPiper; LD=Laughing Dove; S=Shikra.
Table 3. Name, Family and Percentage Abundance, Sightings, Percentage Frequency of Bird Species in Asa Lake, Ilorin, Nigeria._
Common name Scientific name Family % abundance Sighting and % frequency
Grey Heron Ardea cinerea Ardeidae 3.81 Fs; Lc
Black Heron Egretta ardesiaca Ardeidae 3.11 Fs; Lc
Purple Heron Ardea purpurea Ardeidae 3.89 Fs; Lc
Cattle Egret Bubulcus ibis Ardeidae 10.63 C; Co
Water Fowl Anas acuta Anatidae 42.21 C; Co
Whistling Duck Dendrocygna bicolour Anatidae 10.39 C; Co
Blackhead Lapwing Vanellus tectus Charadriidae 2.37 R; Re
Spur winged Lapwing Vanellus spinosus Charadriidae 2.11 R; Re
Wattled Lapwing Vanellus senegalus Charadriidae 1.35 R; Re
Blue breasted Kingfisher Halcyon malimbica Alcedinidae 3.27 Fs; Lc
Pied Kingfisher Ceryle rudis Alcedinidae 2.04 R; Re
Pygmy kingfisher Ispidina picta Alcedinidae 1.51 R; Re
Sand Piper Actitis hypoleucos Scolopacidae 2.12 R; Re
Laughing Dove Streptopelia senegalensis Columbidae 5.16 Fs; Lc
Shikra Accipiter badius Accipitridae 2.22 R; Re
Fish Hawk Pandion haliaetus Pandionidae 1.94 R; Re
African Jacana Actophilornis africanus Jacanidae 0.67 R; Re
Key: R=rare; Fs=frequently seen; C=common; Re=0.00-3.00%; Lc=3.01-9.99%; Co=10.00-100%.
Diversity indices
The diversity indices of the bird species in the lake were as follows; Dominance (D) 0.045, Simpson (1-D) 0.95; Evenness (eAH/S) 0.96, Margalef richness 3.67 and Shanon-Weiner (H) 2.99.
Discussion
This is the first study of water bird assemblages of Asa Lake, Ilorin, Nigeria, an important lake for the supply of domestic and industrial water for a population of about 500,000 people. The abundance, composition and diversity of the bird species in the lake was due to the good limnological heterogeneity of the lake which provided quality habitat for the assemblages of the birds species throughout the sampling period. Suter (1994) showed that trophic status of Lake Ecosystem to be positively correlated with bird abundance.
The assemblages of the birds' species varied significantly with seasons. The high abundance of species in the rainy season could be due to the availability of food resources such as fish and their eggs for the piscivorous species, submerged aquatic macrophytes seeds and foliage which provided food for herbivorous birds and nests/roosts for laying of most aquatic birds eggs, large volume of water and surface area of the lake for movement and gliding by the birds, the depth of the lake which provided fish, and macrobenthic invertebrates as food for the birds, absence of large predators that could prey on the birds in the lake, as well as the season being the reproductive period for most aquatic birds. Malizia (2001) reported an increase of diversity of aquatic birds during the rainy season, while Oliveira (2006) observed migrations of aquatic birds in response to significant variation in water level and resource availability. Donatelli et al., (2013) have also noted large aggregations of birds in the wet season, which he called the ebb period.
Waterfowl and the family Anatidae which were the most abundant species and family in the lake has also been reported in other lakes to be in high abundance (Garay et al., 1991). The reasons for their high abundance could be linked to the reasons advanced above. The diversity of the family Ardeidae was due to the presence of species in the family with different foraging habits, using various behavioural and morphological adaptations to wade in the water and seek different food resources which were available in the lake as well as the morphometric characteristics of the lake which favour their presence and abundance.
The low numbers of African Jacana found in the lake could be due to their feeding preference for insects which were not so abundant in the lake and absence of floating vegetation on the lake on which to lay their eggs. Submerged and emergent aquatic macrophytes are known as habitats and foods for many species of aquatic birds (Knapton & Petrie, 1999), thus influencing their assemblages.
The species commonly seen were primarily aquatic which poses morphological characteristics such as long bill and behavioural tactics such as ability to eat different food sources which are available in the lake. They are mostly seen because most of them are not migratory, been resident in the lake all the time, using the lake as home and nesting place. The rare species are occasionally visitors to the lake, though during the 24 weeks of sampling, they were encountered in every week, only their numbers were low as compared to common and less common species. Their low abundance and rarity could be attributed to their feeding habit (carnivorous) and food preference which include molluscs and crustaceans which were not so abundant in the lake as well as the depth of the lake. Lake depth has been shown to be an important factor influencing distribution and abundance of aquatic birds in lakes and wetland systems (Colwell & Taft, 2000).
Diversity indices of the bird species in the lake is high, this could be due to a high foraging resources available and the good morphometrics of the lake. Hoyer and Canfield (1994), Paszkowski & Tonn (2006) have reported a positive relationship between lake area and its mophometrics as contributing to aquatic bird species richness and assemblages.
Conclusion
The bird species assemblage in Asa Lake, Ilorin, Nigeria shows a high a species diversity and abundance attributed to the to the good water quality and limnological heterogeneity of the lake which provided food resources and submerged aquatic macrophytes for the survival of the birds. For the continued residency and visit of the birds to the lake, lake best management practices (LBMP) should be implemented to prevent water quality deterioration, sedimentation, and anthropogenic materials inflow.
Similarly, continuous monitoring of the birds (bio monitor) in the lake should be done to give an insight into the ecological conditions of the lake and at the same time serving as aesthetic organisms in the lake.
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Citation: Mustapha, M.K., Aiyeleso, O.E. (2018). Aquatic bird assemblages of a tropical African man-made lake. Ukrainian Journal of Ecology, 8(4), 41-45.
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