Kopij 2025, Biologica Nyssana 16(1) 307 16 (1) June 2025: 307-316 DOI: 10.46793/BiolNyss.16.1.14K Inter-annual variation in the structure of avian communities in Zambezi rural riparian forest Original Article Grzegorz Kopij Department of Vertebrate Ecology, Wrocław University of Environmental & Life Sciences, ul. Kożuchowska 5b, 51-631 Wroclaw, Poland grzegorz.kopij@upwr.edu.pl (corresponding author) Received: January 08, 2025 Revised: February 19, 2025 Accepted: March 17, 2025 Abstract: In terms of biodiversity, riparian forests are among the richest habitats in the world, but in the tropical regions of the world, these forests are understudied. In the present study, the avian community was quantified in the Zambezi rural riparian forest in NE Namibia for two years, with a similar rainfall (423 mm in 2013 vs. 428 mm in 2014). In total, 135 breeding bird species were recorded in the study area. Sörensen Similarity Index was I=0.79. There were two dominant species: Quelea quelea and Euplectes orix. The group of subdominants were represented by 11 species. The species composition and population densities only slightly differed between the years 2013 and 2014. The proportions of three main feeding guilds, insectivores, granivores, and frugivores were similar in the riparian forests. This feature distinguishes this community from others studied so far in southern Africa, where either granivores or insectivores are the dominant guilds. Key words: tropical riparian forests, avian community, population density Apstrakt: Međugodišnja varijacija u strukturi zajednica ptica u ruralnim ripari- jalnim šumama reke Zambezi U pogledu biodiverziteta, riparijalne šume spadaju među najbogatija staništa, ali su u tropskim oblastima nedovoljno proučene. U ovoj studiji kvantifikovana je zajednica ptica u ruralnim riparijalnim šumama reke Zambezi na severoistoku Namibije, tokom dve godine, sa sličnim godišnjim vrednostima padavina (423 mm u 2013. i 428 mm u 2014.). Ukupno je zabeleženo 135 vrsta gnezdarica. Sörensenov indeks sličnosti iznosio je I=0,79. Dominantne vrste bile su Quelea quelea i Euplectes orix, dok je grupu subdominantnih činilo 11 vrsta. Sastav vrsta i gustine populacija su blago varirali između analiziranih godina, 2013. i 2014. U smislu ishrane, udeo pripadnika tri glavne gilde (insektivori, granivori i frugivori) bio je sličan u riparijalnim šumama. Ova karakteristika razlikuje ovu zajednicu od drugih u južnoj Africi, gde preovladavaju granivorne ili insektivorne vrste. Ključne reči: tropske riparijalne šume, zajednica ptica, gustina populacije Introduction Among different biomes in southern Africa, the tropical riparian forests appear to be especially rich in terms of biodiversity (Hockey et al., 2005). In Namibia, most of these forests lay in Zambezi, Limpopo and Okavango river valleys (Mucina & Rutherford, 2024). Despite this, little is known about animal communities occupying these forests. It is also true with respect to avian communities, which are often the most intensively studied animal communities in other biomes. In southern Africa, the structure of avian communities has been investigated only in the acacia savanna in Eswatini (Monadjem, 2003; Monadjem, 2005), acacia savanna along Vaal River in South Africa (Seymour & Simmons, 2008) and in the Tamarix vegetation in Karoo, South Africa (Brooke, 1992). In other parts of the world, birds associated with tropical riparian forests are also understudied. Species diversity and community structure of birds were studied along Paraiba do Sul River in Atlantic Forests, Sao Paulo State, Brazil (De Paula Laurenço & de Toledo, 2019); in Alta Foresta, Mato Grosso, Brazil (Lees & Peres, 2008); gallery forests in Costa Rica (Seaman & Schultze, 2010); rainforest in New Guinea (Korejs et al., 2023); monsoonal forest in Hong Kong (Chan et al., 2008); oil palm-forest mosaic in Malaysia (Azman et al., 2011; Michell © 2025 Kopij. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and build upon your work non-commercially under the same license as the original. 308 et al., 2018); savanna in Australia (Woinarski et al., 2000), and forests in south-western Australia (Palmer & Bennett, 2006). The purpose of this study is to determine the structure of an avian community in a rural riparian forest, in terms of: 1) species diversity, 2) domi- nance structure, 3) guilds proportions, and 4) popu- lation densities of particular species making up the community. Study area Studies were conducted in the Zambezi riparian forest in a rural setting. The area is situated near Katima Mulilo, Zambezi Region, NE Namibia. A transect was established along the Zambezi River between 29°83'S, 18°93'E and 29°25'S, 21°30'E (Fig. 1). The riparian forest is interspersed with some traditional rural homesteads with gardens; small fields, pastures for sheep and cattle, water canals (backwaters), grassy depressions flooded almost on an annual basis, and afforested areas with main tree species such as Acacias (Acacia spp.), African Teak (Pterocarpus angolensis), Albizias (Albizia spp.), Apple Leaves (Lonchocarpus nelsii), Burkea (Burkea africana), Combretum (Combretum spp.), Camel-thorn (Acacia erioloba), Jackal Berry (Diospyros mespiliformis), Mopane (Colophospermum mopane), Pod Mahogany (Afzelia quanzensis), Silver Cluster-leaf (Terminalia sericea), Sausage Tree (Kigelia africana), Sycamore Fig (Ficus sycomorus), White Bauhinia (Bauhinia petersiana), Zambezi Teak (Baikiaea plurijuga), and Silver Tree (Terminalia sericea). BIOLOGICA NYSSANA ● 16 (1) June 2025: 307-316 Kopij ● Inter-annual variation in the structure of avian communities in Zambezi rural riparian forest Fig. 1. The location of the transect (yellow line) along the Zambezi River Fig. 2. Monthly rainfall in Katima Mulilo in 2013 and 2014 309 BIOLOGICA NYSSANA ● 16 (1) June 2025: 307-316 Kopij ● Inter-annual variation in the structure of avian communities in Zambezi rural riparian forest The monthly distribution of rainfall in 2013 and 2014 is shown in Fig. 2. The total amount of rainfall was similar in both years (423 mm in 2013 vs. 428 mm in 2014). Methods The line transect method in the American version (Sutherland, 1996; Bibby et al., 2012) has been employed to quantify avian assemblages (frequency of occurrence and relative abundance of each species) along the designed transect. Counts on transects were conducted three times (February/ March, May, September), both in 2013 and 2014. The transect was 6 km long. Counts were conducted in the mornings by walking slowly from c. 6 a.m. till c. 11 a.m. and recording all birds seen and heard. For resident birds, a breeding pair was a census unit, while for non- resident species, the census unit was an individual. A bird calling and/or showing other territorial or breeding behaviour was regarded as an actual breeder, i.e. it represented a breeding pair. Caution was taken to not register the same individuals by noting the movements of counted birds in the field and by paying special attention to simultaneously calling birds. Following assumptions of the line transect method, the maximal number of breeding pairs on the transect in whatever of the three counts conducted in a given year was assumed as the number of all potentially breeding birds (Bibby et al., 2012). The dominance of each species is expressed as the percentage of the total number of pairs of a given species in relation to the total number of all pairs of all species recorded. Dominant species: >5%, subdominant: 2-4.99%. The following guilds were distinguished: Diet: G – granivorous, I – insectivorous, F – frugivorous, N – nectarivorous, R – carnivorous. Nesting: T – in trees or shrubs, H – in holes, B – in/ on buildings, V – herbaceous vegetation. Habitat: F – forest interior, E – ecotone (forest/open area), O – „open” area (grassland/savanna). Residency: R – resident throughout the year, A – intra-African migrant, C – nomad. The following indices were used to characterize the diversity and evenness of the communities: 1) Shannon’s diversity index: H’=-∑ pi ln pi where: pi is the proportion of breeding pairs belonging to the ith species 2) Simpson’s diversity index: D=((∑n(n-1))/N(N-1) where: n is the total number of breeding pairs belonging to a given species, N is the total number of breeding pairs of all species 3) Pielou’s evenness index: J’=(-∑ pi ln pi)/ln S, where: pi is the proportion of breeding pairs belonging to the ith species; S is the total number of species. J’ varies between 0 and 1. The less variation between species in a community, the higher J’ is. 4) Community dominance index: DI=(n1+n2)/N where: n1, n2 is number of pairs of two most abundant species, N is total number of pairs of all species. 5) Sörensen’s Coefficient: I=2C/A+B where: A is the number of bird species in one breeding season, B is the number of bird species in another breeding season, and C is the number of bird species common to both breeding seasons. The ch2-test was used to test differences in population densities between 2013/14 and 2015/16. For statistical testing, only those species with at least 10 breeding pairs in both seasons were included. Systematics and nomenclature of bird species follow Hockey et al. (2005), with later nomenclatorial changes. Results In 2013-2014, a total of 135 breeding bird species were recorded in the study area: 103 species in 2013, 118 species in 2014 (Tabs. 1 and 2); 87 species were common for 2013 and 2014. Sörensen similarity Index was I=0.79. In addition, 7 non-breeding Palearctic species were recorded: 3 in 2014 and 6 in 2015. There were two dominant species: Red-billed Quelea Quelea quelea and Southern Red Bishop Euplectes orix. Both are nomad breeders; the Red- billed Quelea was recorded as dominant in 2013 and was not recorded at all in the next year. On the other hand, the Southern Red Bishop was recorded as dominant in 2014, while in 2013 it was uncommon (0.2%). The group of subdominants were represented by 11 and 9 species in 2013 and 2014 respectively, as listed in Tab. 1. The following species were subdominants in both years: Cercotrichas leucophrys, Lybius torquatus, Phyllastrephus terrestris, Prinia subflava, Streptopelia capicola, Turtur chalcospilos, and Uraeginthus angolensis. The following species were more common (sta- tistically significant difference) in 2013 than in 2014: Cercotichas leucophrys, Francolinus sephae- na, Lamprotornis australis, Mirafra rufocinnamo- mea, Nettapus auratus, Telophorus sulfureopectus, Trachyphonus vaillantii, and Vidua macroura. On the other hand, more common in 2014 than in 2013 were Dicrurus adsimilis, Euplectes orix, Ploceus ve- latus, Spilopelia senegalensis, Streptopelia semitor- quata, and Turtur chalcospilos. The abundance of 26 species was not significantly different in 2013 and 2014. For 19 species the numbers of breeding pairs were identical in both years (Tab. 2). 310 BIOLOGICA NYSSANA ● 16 (1) June 2025: 307-316 Kopij ● Inter-annual variation in the structure of avian communities in Zambezi rural riparian forest Table 1. Characteristics of the breeding bird community Parameter 2013 2014 Number of species and breeding pairs Number of spp. 103 118 Number of pairs 823 801 Overall density 137.2 133.5 Dominance structure Dominance index 0.17 0.19 Number of dominant species 1 1 Percentage of dominants 12.2 14.4 Number of subdominant species 11 9 Percentage of subdominants 34.5 27.7 Diversity indices H’ 3.95 4.06 J’ 0.85 0.85 D 0.97 0.97 Table 2. Number of breeding pairs, linear density and dominance of birds breeding in a riparian forest (6 km) in a rural setting in 2013 and 2014. Explanations: N – number of breeding pairs, D – linear density (pairs per km), Dom – dominance Species 2013 2014 X2-test N D Dom N D Dom Accipiter spp. 0 0 0.0 1 0.2 0.1 Actophilornis africanus 6 1 0.7 6 1 0.7 0.0 Alopochen aegyptiacus 1 0.2 0.1 0 0 0.0 Anastomus lamelligerus 1 0.2 0.1 0 0 0.0 Anthoscopus caroli 0 0 0.0 1 0.2 0.1 Apalis flavida 10 1.7 1.2 10 1.7 1.2 0.0 Apus affinis 0 0 0.0 2 0.3 0.2 Ardea ibis 2 0.3 0.2 9 1.5 1.1 4.1* Ardeola ralloides 1 0.2 0.1 1 0.2 0.1 Batis molitor 5 0.8 0.6 10 1.7 1.2 1.9 Bostrychia hagedash 1 0.2 0.1 1 0.2 0.1 Bucorvus leadbeateri 1 0.2 0.1 0 0 0.0 Buphagus erythrorhynchus 3 0.5 0.4 0 0 0.0 Butorides rufiventris 2 0.3 0.2 0 0 0.0 Butorides striatus 0 0 0.0 1 0.2 0.1 Bycanistes bucinator 2 0.3 0.2 2 0.3 0.2 Camaroptera brevicaudata 0 0 0.0 1 0.2 0.1 Campephaga flava 0 0 0.0 1 0.2 0.1 Most species were breeding, either as African residents or infra-African migrants. Seven species (Merops apiaster, Acrocephalus arundinaceus, Acrocephalus palustris, Hirundo rustica, Lanius collurio, Muscicapa striata, and Phylloscopus trochilus) were non-breeding Palearctic migrants. In 2013, the proportion of Palearctic migrants (159 individuals of three species) was much higher than in 2014 (18 individuals of six species) because there was an influx of c. 150 individuals of Merops apiaster in 2013 (none recorded 2014). Among breeding birds, most were African residents; very few were intra-African migrants (0.6% and 0.2% in 2013 and 2014 respectively). The proportions of main feeding guilds were much the same in 2013 and 2014 (Fig. 3). The main nesting guild was tree/shrub nesting birds, with similar proportions in 2013 and 2014 (Fig. 3). However, the proportion of hole-nesting birds was much higher in 2013 than in 2014, while in the case of the guild nesting in herbaceous vegetation, the reverse was recorded (much higher proportion in 2014 than in 2013). 311 BIOLOGICA NYSSANA ● 16 (1) June 2025: 307-316 Kopij ● Inter-annual variation in the structure of avian communities in Zambezi rural riparian forest Campethera abingoni 3 0.5 0.4 2 0.3 0.2 Centropus cupreicaudus 5 0.8 0.6 5 0.8 0.6 0.0 Centropus senegalensis 4 0.7 0.5 4 0.7 0.5 Centropus spp. 0 0 0.0 4 0.7 0.5 Centropus superciliosus 10 1.7 1.2 6 1 0.7 2.0 Cercotrichas leucophrys 33 5.5 4.0 22 3.7 2.7 4.1* Ceryle rudis 2 0.3 0.2 8 1.3 1.0 3.4 Chlorocichla flaviventris 9 1.5 1.1 9 1.5 1.1 0.0 Chrysococcyx cupreus 0 0 0.0 1 0.2 0.1 Cinnyricinclus leucogaster 0 0 0.0 5 0.8 0.6 Circaetus cinerascens 1 0.2 0.1 1 0.2 0.1 Circus ranivorous 1 0.2 0.1 0 0 0.0 Cisticola chiniana 17 2.8 2.1 14 2.3 1.7 0.5 Cisticola juncidis 0 0 0.0 8 1.3 1.0 Cisticola spp. 0 0 0.0 2 0.3 0.2 Coracias caudata 2 0.3 0.2 2 0.3 0.2 Corvinella melanoleuca 1 0.2 0.1 0 0 0.0 Corvus albus 2 0.3 0.2 2 0.3 0.2 Corythaixoides concolor 11 1.8 1.3 14 2.3 1.7 0.5 Crithagra atrogularis 5 0.8 0.6 1 0.2 0.1 Dendrocygna viduata 0 0 0.0 1 0.2 0.1 Dicrurus adsimilis 1 0.2 0.1 13 2.2 1.6 8.3* Dondropicos fuscescens 2 0.3 0.2 3 0.5 0.4 Dryoscopus cubla 7 1.2 0.9 7 1.2 0.9 0.0 Egretta garzetta 0 0 0.0 1 0.2 0.1 Emberiza flaviventris 0 0 0.0 2 0.3 0.2 Eyrystomus glaucurus 0 0 0.0 1 0.2 0.1 Erythropygia leuconotus 10 1.7 1.2 10 1.7 1.2 0.0 Estrilda astrild 12 2 1.5 7 1.2 0.9 2.7 Euptectes orix 2 0.3 0.2 115 19.2 14.4 83.3** Falco dickinsoni 2 0.3 0.2 0 0 0.0 Falco rupicoloides 0 0 0.0 1 0.2 0.1 Francolinus sephaena 12 2 1.5 3 0.5 0.4 20.3** Francolinus swainsonii 2 0.3 0.2 3 0.5 0.4 Halcyon albiventris 0 0 0.0 2 0.3 0.2 Halcyon leucocephala 1 0.2 0.1 1 0.2 0.1 Halcyon senegalensis 2 0.3 0.2 3 0.5 0.4 Haliaeetus vocifer 5 0.8 0.6 3 0.5 0.4 Hedydipna collaris 2 0.3 0.2 1 0.2 0.1 Hirundo abyssinica 6 1 0.7 18 3 2.2 312 BIOLOGICA NYSSANA ● 16 (1) June 2025: 307-316 Kopij ● Inter-annual variation in the structure of avian communities in Zambezi rural riparian forest Hirundo smithii 0 0 0.0 4 0.7 0.5 Indicator indicator 1 0.2 0.1 0 0 0.0 Indicator minor 1 0.2 0.1 1 0.2 0.1 Kaupifalco monogrammicus 1 0.2 0.1 0 0 0.0 Lagonosticta senegala 11 1.8 1.3 7 1.2 0.9 1.7 Lagonosticta nitidula 0 0 0.0 1 0.2 0.1 Lamprotornis australis 14 2.3 1.7 1 0.2 0.1 126.8** Lamprotornis nitens 6 1 0.7 8 1.3 1.0 0.4 Laniarius bicolor 14 2.3 1.7 11 1.8 1.4 0.6 Lophaetus occipitalis 0 0 0.0 1 0.2 0.1 Lybius torquatus 26 4.3 3.2 18 3 2.2 2.7 Matacilla aguimp 1 0.2 0.1 1 0.2 0.1 Merops bullockoides 1 0.2 0.1 6 1 0.7 Merops hirundineus 1 0.2 0.1 0 0 0.0 Merops nubicoides 1 0.2 0.1 6 1 0.7 Merops pusillus 7 1.2 0.9 5 0.8 0.6 Micronisus gabar 0 0 0.0 1 0.2 0.1 Milvus eagyptius 3 0.5 0.4 1 0.2 0.1 Mirafra rufocinnamomea 13 2.2 1.6 1 0.2 0.1 108.0** Muscicapa caerulescens 0 0 0.0 1 0.2 0.1 Myioparus plumbeus 0 0 0.0 1 0.2 0.1 Nattapus auritus 14 2.3 1.7 4 0.7 0.5 18.8* Nectarinia mariquensis 12 2 1.5 7 1.2 0.9 2.7 Nectarinia senegalensis 0 0 0.0 2 0.3 0.2 Nectarinia talatala 4 0.7 0.5 3 0.5 0.4 Nectarinidae spp. 17 2.8 2.1 17 2.8 2.1 0.0 Nilaus afer 7 1.2 0.9 5 0.8 0.6 0.6 Oriolus auratus 0 0 0.0 4 0.7 0.5 Oriolus larvatus 1 0.2 0.1 1 0.2 0.1 Ortygospiza atricollis 1 0.2 0.1 2 0.3 0.2 Parus niger 1 0.2 0.1 4 0.7 0.5 Passer diffusus 2 0.3 0.2 3 0.5 0.4 Phalacrocorax africanus 7 1.2 0.9 8 1.3 1.0 0.1 Phoeniculus purpureus 2 0.3 0.2 6 1 0.7 Phyllastrephus terrestris 31 5.2 3.8 21 3.5 2.6 3.6 Plectropterus gambensis 0 0 0.0 9 1.5 1.1 Ploceus velatus 18 3 2.2 5 0.8 0.6 25.4** Pogoniulus chrysocomus 8 1.3 1.0 7 1.2 0.9 0.1 Poicephalus meyeri 5 0.8 0.6 3 0.5 0.4 Prinia subflava 32 5.3 3.9 23 3.8 2.9 2.6 Prinia flavicans 0 0 0.0 1 0.2 0.1 Prionops plumatus 2 0.3 0.2 2 0.3 0.2 Prionops retzii 0 0 0.0 5 0.8 0.6 313 BIOLOGICA NYSSANA ● 16 (1) June 2025: 307-316 Kopij ● Inter-annual variation in the structure of avian communities in Zambezi rural riparian forest Pytilia afra 1 0.2 0.1 1 0.2 0.1 Quelea quelea 100 16.7 12.2 0 0 0.0 Rhinopomastus cyanomelas 2 0.3 0.2 3 0.5 0.4 Spermestes cucullatus 0 0 0.0 1 0.2 0.1 Spilopelia senegalensis 2 0.3 0.2 14 2.3 1.7 7.7* Streptopelia capicola 20 3.3 2.4 31 5.2 3.9 2.9 Streptopelia decipiens 0 0 0.0 4 0.7 0.5 Streptoperia semitroquata 10 1.7 1.2 21 3.5 2.6 4.3* Sylvietta rufescens 6 1 0.7 3 0.5 0.4 Tachybaptus ruficollis 1 0.2 0.1 0 0 0.0 Tauraco schalowi 13 2.2 1.6 12 2 1.5 0.1 Tchagra australis 1 0.2 0.1 1 0.2 0.1 Tchagra senegala 0 0 0.0 3 0.5 0.4 Tchagra spp. 1 0.2 0.1 3 0.5 0.4 Telophorus sulfureopectus 14 2.3 1.7 7 1.2 0.9 5.3* Thalassornis leuconotus 4 0.7 0.5 0 0 0.0 Tockus erythrorhynchus 1 0.2 0.1 0 0 0.0 Tockus nasutus 8 1.3 1.0 10 1.7 1.2 0.3 Trachyphonus vaillantii 18 3 2.2 10 1.7 1.2 4.8* Treron calva 4 0.7 0.5 1 0.2 0.1 Tringa glareola 1 0.2 0.1 0 0 0.0 Turdides jardineii 8 1.3 1.0 1 0.2 0.1 Turdoides hartlaubii 3 0.5 0.4 8 1.3 1.0 2.3 Turdus libonyanus 0 0 0.0 1 0.2 0.1 Turnix sylvatica 1 0.2 0.1 1 0.2 0.1 Turtur chalcospilos 20 3.3 2.4 36 6 4.5 5.3* Upupa epops 16 2.7 1.9 5 0.8 0.6 18.2** Uraeginthus angolensis 38 6.3 4.6 31 5.2 3.9 1.2 Urocolius indicus 19 3.2 2.3 13 2.2 1.6 2.1 Vanellus armatus 2 0.3 0.2 2 0.3 0.2 Vanellus senegallus 6 1 0.7 4 0.7 0.5 0.8 Vidua halybeata 0 0 0.0 1 0.2 0.1 Vidua macroura 30 5 3.6 4 0.7 0.5 126.8** Zosterops senegalensis 1 0.2 0.1 1 0.2 0.1 Total number of pairs 823 100.0 801 100.0 Discussion In total, 135 bird species were recorded in the riparian forest (this study, Tab. 2). In the neighbouring Mopane-Terminalia forest and Kalahari Woodland mixed with rural areas, the numbers were much lower, i.e. 51 and 56, respectively (Tab. 3). In the Mopane Woodland, situated in north-central Namibia, the number of breeding species was 85 (Kopij, 2013a and 2013b), while in the Kaokoland Savanna, in 314 NW Namibia, it was 64 (Kopij, 2014b). It is clear, therefore, that in Namibia, the number of breeding bird species declines westwards, i.e. with declining precipitation (Mendelsohn et al., 2009). However, within the same region, it may differ markedly depending on the soil type, inundation and topography. All these factors affect, in turn, variance in vegetation type. There were more breeding species in the riparian forest than in other forest types situated in the Zambezi region. Also the population densities of many species were much higher in the riparian forests than in the other forest types (Tab. 3). Out of 32 species compared, only Grey-backed Camaroptera (Camaroptera brevicaudata), Southern Grey-headed Sparrow (Passer diffusus), Lilac-breasted Roller (Coracias caudatatus), and Red-billed Hornbill (Tockus erythrorhynchus) were less numerous in the riparian forests than in other forest types. In terms of the number of breeding pairs, the proportions of the three main feeding guilds: insectivores, granivores, and frugivores were similar in the riparian forests. However, in terms of the number of species, insectivores comprised almost half of this assemblage. This feature distinguishes this community from others studied so far in southern Africa, where either granivores or insectivores were the dominant guilds (Kopij, 2000, 2001a, 2001b, 2006, 2013a, 2013b, 2014a, 2014b, 2015, 2016, 2017, 2018, 2021, 2022). In riparian forests of Africa, the fruit trees are usually abundant and may benefit frugivorous birds (especially bulbuls), while seeds may not be so abundant, as these are in more open savanna or grassland biomes. Typical granivores, such as doves and sparrows, may therefore breed in lower densities in riparian forests than in the neighbouring more open habitats dominated by grasses. The species composition only slightly differed between the years 2013 and 2014. There was also no shift in species diversity, or in the community structure. This interannual stability can be linked to almost the same level BIOLOGICA NYSSANA ● 16 (1) June 2025: 307-316 Kopij ● Inter-annual variation in the structure of avian communities in Zambezi rural riparian forest Fig. 2. Proportions of feeding (columns in the upper row) and nesting guilds (columns in the lower row) in 2013. and 2014 Table 3. Linear population densities (pairs per 1 km of transect) of selected bird species (=32) in different forest types in rural settings in the Zambezi Region. Habitat types: 1) Riparian forest (this study), 2) Mopane/Terminalia forest (Kopij, 2022), 3) Kalahari Woodland (Kopij, 2021) Species Habitat types 1 2 3 Batis molitor 1.7 0.2 1.3 Camaroptera brevicaudata 0.2 0 1.3 Cercotrichas leucophrys 5.5 0.9 0 Chlorocichla flaviventris 1.5 0 1.1 Cisticola chiniana 2.8 0 0.7 Cisticola juncidis 1.3 0 0.2 315 BIOLOGICA NYSSANA ● 16 (1) June 2025: 307-316 Kopij ● Inter-annual variation in the structure of avian communities in Zambezi rural riparian forest of precipitation in these two years compared. The amount of rainfall is usually the main limiting factor governing both the distribution and population densities of most bird species in Africa (Maclean, 1990). A high number of species and high densities of their populations compared to other forest types in the Zambezi Region (Tab. 3) suggest that riparian forests play an important role as breeding and feeding habitat for birds, especially frugivores and nectarivores. It may also play a role as a corridor allowing dispersal, migration and free movements within a mosaic of natural and human-modified environments (Seaman & Schulze, 2010). The riparian forest corridor may be therefore considered as a main instrument to offset the negative effects of habitat loss and fragmentation (Turner, 1996; Lees & Peres, 2008), and for that reason, it deserves special protection. References Azman, N.M., Latip, N.S.A., Sah, S.A.M., Akil, M.A.M.M., Shafie, N.J., & Khairuddin, N.L. (2011). Avian diversity and feeding guilds in a secondary forest, an oil palm plantation and a paddy field in Riparian areas of the Kerian River Basin, Perak, Malaysia. Tropical Life Sciences Research, 22(2), 45-64. Bibby, C.J., Burgess, N.D., Hill D.A. & Mustoe, S. (2012). Bird Census Techniques (2nd ed.). London: Academic Press Brooke, R.K. (1992). The bird community of Tamarix-clad drainages, northwestern Karoo, Cape Province. Ostrich - Journal of African Ornithology, 63(1), 42-43. Chan, E.K., Yu, Y.T., Zhang, Y., & Dudgeon, D. (2008). Distribution patterns of birds and insect prey in a tropical riparian forest. Biotropica, 40(5), 623-629. De Paula Laurenço, A.C.P. & de Toledo M.C.B. (2019). Effects of proximity to urban areas on a riparian bird community in remnant Atlantic Forest in southeastern Brazil. Ambiente e Agua - An Interdisciplinary Journal of Applied Science, 14(7), 1-18. Hockey, P.A., Dean, W.R.J., Ryan, P.G., Maree, S., & Brickman, B.M. (Eds.) (2005). Robert’s Birds of Southern Africa. Cape Town: Trustees of the John Voelcker Bird Book Fund Kopij, G. (2000). Birds of Maseru. National University of Lesoto Journal of Research, 8, 104- 151. Kopij, G. (2001a). Atlas of Birds of Bloemfontein. Lesotho, Roma / Republic of South Africa, Bloemfontain: Department of Biology, National University of Lesotho / Free State Bird Club Kopij, G. (2001b). Birds of Roma Valley, Lesotho. Lesotho, Roma: Department of Biology, National University of Lesotho Kopij, G. (2006). The Structure of assemblages and dietary relationships in birds of South African Coracias caudatus 0.3 0.2 0.7 Corythaixoides concolor 2.3 0.7 1.3 Dicrurus adsimilis 2.2 1.2 1.3 Dondropicos fuscescens 0.5 0.1 0.2 Dryoscopus cubla 1.2 0 0.7 Laniarius bicolor 2.3 0 1.1 Lybius torquatus 4.3 0.1 1.0 Nilaus afer 1.2 0.1 0.2 Passer diffusus 0.5 1.2 0.2 Phyllastrephus terrestris 5.2 0 0.7 Ploceus velatus 3.0 0.3 0 Pogoniulus chrysocomus 1.3 0 0.2 Poicephalus meyeri 0.8 0 1.6 Prinia subflava 5.3 0.2 0.4 Spilopelia senegalensis 2.3 0 2.0 Streptopelia capicola 5.2 2.6 6.7 Streptopelia decipiens 0.7 0 0 Streptopelia semitroquata 3.5 0.1 1.3 Telophorus sulfureopectus 2.3 0.1 0.4 Tockus erythrorhynchus 0.2 0.7 0 Tockus nasutus 1.7 1.1 0.9 Trachyphonus vaillantii 3.0 0.3 0 Turtur chalcospilos 6.0 0.3 3.1 Upupa epops 2.7 0.3 0 Uraeginthus angolensis 6.3 2.0 5.6 Urocolius indicus 3.2 0.2 0 Number of all pairs 823 409 338 Number of all breeding species 135 56 51 316 BIOLOGICA NYSSANA ● 16 (1) June 2025: 307-316 Kopij ● Inter-annual variation in the structure of avian communities in Zambezi rural riparian forest grasslands. Wrocław: Wydawnictwo Akademii Rolniczej. Kopij, G. (2013a). Avian assemblages in natural and modified Kaokoland (Mopane) Savanna in the Cuvelai Drainage System, north-central Namibia. Lanioturdus, 46(5), 22-33. Kopij, G. (2013b). Seasonal changes in avian assemblages in Kaokoland (Mopane) Savanna in the Ogongo Game Reserve, north-central Namibia. International Science & Technology Journal of Namibia, 2(1), 44-58. Kopij, G. (2014a). Avian assemblages of urban habitats in north-central Namibia. International Science & Technology Journal of Namibia, 3(1): 64-81. Kopij, G. (2014b). Avian communities of a mixed Mopane-Acacia Savanna in the Cuvelai Drainage System, North-Central Namibia, during the dry and wet season. Vestnik Zoologii, 48(4), 269-274. Kopij, G. (2015). Avian diversity in an urbanized South African grassland. Zoology & Ecology, 25(2), 87-100. Kopij, G. (2016). Birds of Katima Mulilo town, Zambezi Region, Namibia. International Science & Technology Journal of Namibia, 7, 85-102. Kopij, G. (2017). Structure of avian assemblages in Zambezian Baikiaea woodlands, northern Namibia. Zoology & Ecology, 27(1), 1-10. Kopij, G. (2018). Provisional atlas of breeding birds of Swakopmund in the coastal Namib Desert. Lanioturdus, 51(2), 2-12. Kopij, G. (2021). Effect of farming and rainfall on the species diversity, population density and community structure of birds breeding in the Kalahari Woodland, NE Namibia. Zoodiversity, 55(6), 451-458. Kopij, G. (2022). Effect of a road on avian diversity in Kalahari woodland. Zoology and Ecology, 32(1), 1-8. Korejs, K., Riegert, J., Kigl, M., & Novotny, V. (2023). Differences in bird community structure between riparian and upland zones in a New Guinean rainforest. Australian Field Ornithology, 40, 179- 195. Lees, A.C. & Peres, C.A. (2008). Conservation value of remnant riparian forest corridors of varying quality for Amazonian birds and mammals. Conservation Biology, 22(2), 439-449. Maclean, G.L. (1990). Ornithology for Africa. Pietermaritzburg: University of KwaZulu Natal Press Mendelsohn, J., Jarvis, A., Roberts, C., & Robertson, T. (2009). Atlas of Namibia. A Portrait of the Land and its People. Cape Town: Sunbird Publishers Michell, S.L., Edwards, D.P., Bernard, H., Coomes, D., Jucker, T., Davies, Z.G., & Struebig, M.J. (2018). Riparian reserves help protect forest bird communities in oil palm dominated landscapes. Journal of Applied Ecology, 55(6), 2744-2755. Monadjem, A. (2003). Population densities and community structure of birds in riverine forest in the lowveld of Swaziland. Ostrich - Journal of African Ornithology, 74(3-4), 173-180. Monadjem, A. (2005). Associations between avian communities and vegetation structure in a low-lying woodland-savanna ecosystem in Swaziland. Ostrich - Journal of African Ornithology, 76(1-2), 45-55. Mucina, L. & Rutherford, M.C. (2024). Zonal Biomes of Southern Africa. Switzerland, Cham: Springer Palmer, G.C. & Bennett, A.F. (2006). Riparian zones provide for distinct bird assemblages in forest mosaics of south-east Australia. Biological Conservation, 130(3), 447-457. Seaman, B.C. & Schulze, C.H. (2010). The importance of gallery forests in the tropical lowlands of Costa Rica for understorey forest birds. Biological Conservation, 143(2), 391-398. Seymour, C.L. & Simmons, R.E. (2008). Can severely fragmented patches of riparian vegetation still be important for arid-land bird diversity. Journal of Arid Environment, 72(12), 2275-2281. Sutherland, W.J. (1996). Ecological Census Techniques: a handbook. United Kingdom, Cambridge: Cambridge University Press Turner, I.M. (1996). Species loss in fragments of tropical rain forest: a review of the evidence. Journal of Applied Ecology, 33, 200-209. Woinarski, J.C.Z., Brock C., Armstrong M., Hempel, C., Cheal, D., & Brennan, K. (2000). Bird distribution in riparian vegetation in the extensive natural landscape of Australia’s tropical savanna: a broad-scale survey and analysis of a distributional data base. Journal of Biogeography, 27(4), 843-868.