Coraciformes, Cens, Bosc de rivera, Densitat de població
Data de recepció: 26/04/2019 | Data d'acceptció: 25/09/2019 | Data de publicació: 10/10/2019
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Diversity and population densities of coraciiform birds in Zambezi riparian forest
Diversity and population densities of coraciiform birds in Zambezi riparian forest
A territory mapping method was used in 2015 to assess the population density of coraciiform species breeding in a riparian forest on the Zambezi River near Katima Mulilo, NE Namibia. The forest, c. 280 ha in surface area, was partly transformed by human settlement and arable grounds. A total of 13 species and 42 breeding pairs were recorded. Population densities were (pairs per 100 ha) as follows: grey-headed kingfisher 4.3; giant, pied and woodland kingfisher each one with 1.1; malachite kingfisher 0.7; striped kingfisher 0.4; white-fronted bee-eater 1.4; little bee-eater 1.1; lilac-breasted roller 0.7; broad-billed roller 1.1; African hoopoe 0.7; red-billed wood-hoopoe 1.1; and scimitar-billed wood-hoopoe 0.4.
Data published through GBIF (Doi: 10.15470/s9rlud).
Key words: Coraciiformes, Census, Riparian forest, Population density
Diversidad y densidades de población de aves coraciformes en un bosque de rivera de Zambeze
En el año 2015 se empleó un método de mapeo del territorio para evaluar la densidad de población de las especies de coreciformes que se reproducen en un bosque de ribera del río Zambeze, en las proximidades de Katima Mulilo, al NE de Namibia. El bosque, de unas 280 hectáreas de superficie, está parcialmente transformado por asentamientos humanos y tierras de cultivo. Se registraron un total de 13 especies y 42 parejas reproductoras. Se establecieron las siguientes densidades de población (parejas por 100 ha): alción cabeciblanco 4,3; martín gigante africano, martín pescador pío y alción senegalés 1,1 cada uno; martín pescador malaquita 0,7; alción estriado 0,4; abejaruco frentiblanco 1,4; abejaruco chico 1,1; carraca lila 0,7; carraca picogorda 1,1; abubilla africana 0,7; abubilla arbórea verde 1,1, y abubilla arbórea cimitarra 0,4.
Datos publicados en GBIF (Doi: 10.15470/s9rlud).
Palabras clave: Coraciformes, Censo, Bosque de rivera, Densidad de población
Diversitat i densitats de població d’ocells coraciformes en un bosc de rivera de Zambeze
L’any 2015 es va utilitzar un mètode de mapatge del territori para avaluar la densitat de població de les espècies de coreciformes que es reprodueixen en un bosc de ribera del riu Zambeze, prop de Katima Mulilo, al NE de Namíbia. El bosc, d’unes 280 hectàrees de superfície, està parcialment transformat per assentaments humans i terres de conreu. S’hi van registrar un total de 13 espècies y 42 parelles reproductores. S’hi van establir les densitats de població següents (parelles per 100 ha): alció capgris 4,3; alció gegant africà, alció garser i alció del Senegal 1,1 cadascun; blauet malaquita 0,7; alció estriat 0,4; abellerol frontblanc 1,4; abellerol petit 1,1; gaig blau de clatell verd 0,7; gaig becgròs africà 1,1; puput africana 0,7; puput arbòria verda 1,1, i puput arbòria simitarra 0,4.
Dades publicades a GBIF (Doi: 10.15470/s9rlud).
Paraules clau: Coraciformes, Cens, Bosc de rivera, Densitat de població
Coraciiforms (kingfishers, bee-eaters, rollers and allies) belong to a highly attractive group of birds and may play an important ecological role in some habitats. They are especially well-represented in sub-Saharan Africa where they are grouped in three families: bee-eaters (Meropidae), rollers (Coracidae) and kingfishers (Alcedinidae). Some authorities also include the hoopoe (Upupidae) and wood-hoopoe (Phoeniculidae) families, as I also do in this study.
Many southern African species belonging to the order Coraciiformes are relatively well-studied (e.g. Fry et al., 1992), especially in regard to their breeding biology and diet (Kopij, 2000; 2018a). However, little information on population density is yet available for most of them (Hockey et al., 2005). Since many coraciiform species breed in low densities, such studies are difficult because they have to be conducted on relatively large study plots.
This note reports on the distribution and population density of coraciiform species breeding in a riparian forest in NE Namibia. Since the riparian forest is under threat of degradation, it is important to create a basis for monitoring bird species that may be indicative of habitat naturalness.
Material and methods
The study area was located in the Zambezi Valley near Katima Mulilo in the Zambezi Region, NE Namibia. The study area comprised a forest stretching between the river and the international road from Zambia through Katima Mulilo to Botswana, lying on the left bank between the Wenela Bridge (border pass) and the Zambezi River lodge. This forest area is 7 km long and 200-700 m wide (mean = c. 400 m). The approximate surface area is therefore c. 280 ha.
The natural vegetation is classified as Riparian Zambezi Forest (Mendelsohn et al., 2009). It is composed of large trees such as African teak Pterocarpus angolensis, Albizias Albizia spp., apple leaf Lonchocarpus nelsii, baobab Adansonia digitata, burkea Burkea africana, combretum Combretum spp., camel-thorn Acacia erioloba, corkwoods Commiphora spp., false mopane Guibourtia coleospermum, Jackal berry Diospyros mespiliformis, knob-thorn Accacia nigrescens, Makalani palm Hyphaene petersiana, manketti Schinziophyton rautanenii, marula Sclerocarya birrea, mopane Colophospermum mopane, pod mahogany Afzelia quanzensis, silver cluster-leaf Terminalia sericea, sausage tree Kigelia africana, sycomore fig Ficus sycomorus, white bauhinia Bauhinia petersiana, Zambezi Tteak Baikiaea plurijuga.
The forest is interlaced with pans covered with grass and sedges flooded almost on a yearly basis. About one quarter of the land has been converted into arable grounds and built-up areas, but large trees usually remain even in these converted areas (fig. 1).
The annual temperature for Katima Mulilo is 21 ºC. The average maximum temperature during the hottest month (September) is 35 ºC; the average minimum temperature during the coldest month (July) is 3 ºC. Humidity is 80-90 % in the most humid month (February) and only 10-20 % in the least humid month (September). The average annual rainfall is c. 700 mm, the highest in Namibia. Median annual rainfall is 550-600 mm. Most rains fall between November and March. The rainfall was below the long-term average in 2014 and in 2015 (fig. 2).
A territory mapping method (Bibby et al., 2002) was used to assess the population densities of all coraciiform species nesting in the forest. The study area was divided into six sections. Birds were counted in each of the sections in one morning.Therefore, the whole study area was covered in six mornings. Such complete coverage was achieved four times in 2015, in August, September, October and November. During each count, all coraciiform birds seen or heard were plotted on the map 1:500. Special attention was paid to birds showing territorial behaviour or breeding display. Recordings of two or three simultaneously calling males were important in interpreting the results. A bird or pair of the same species recorded at the same site in at least two out of the four months was interpreted as residential/breeding/territorial (following Bibby et al., 2002).
Results and discussion
In total 13 coraciiform species were recorded as breeding in 2016: six kingfishers, two bee-eaters, two rollers, two wood-hoopoes, and one hoopoe species.
The coraciiform community in the riparian forest was dominated by kingfishers, which comprised more than 50 % of all breeding coraciiform species. By far, the most numerous kingfisher species was the grey-headed kingfisher Halcyon leucocephala comprising exactly half of all breeding pairs of kingfishers and nested in a density of 4.3 pairs/100 ha. Three other kingfisher species, the woodland Halcyon senegalensis, pied Ceryle rudis and giant kingfisher Megaceryle maximus, all nested in the same density (i.e. 1.1 pairs/100 ha). There were also two pairs of the malachite kingfisher Alcedo cristata (0.7 pair/100 ha). The least numerous was the striped kingfisher Halcyon chelicuti (table 1).
The bee-eaters were represented by the white-fronted bee-eater Merops bullockoides breeding in a small colony on the bank of the river, and the little bee-eater Merops pisillus breeding in a built-up area within the forest. Overall density of bee-eaters was 2.5 pairs/100 ha (table 1).
Territories of three pairs of the broad-billed roller Eurystomus glaucurus and two territories of the lilac-breasted roller Coracias caudatus were recorded in the area. Rollers nested, therefore, in a density of 1.3 pairs/100 ha (table 1).
There were also two pairs of the African hoopoe Upupa africana, three breeding units of the red-billed wood-hoopoe Phoeniculus purpureus and one pair of the scimitar-billed wood-hoopoe Rhinopomastus cyanomelas. The overall density of all hoopoes and wood-hoopoes was 2.1 pairs/100 ha.
Out of 42 breeding pairs of coraciiform birds, 15 territories have been established in a pure forest (35.7 %), 9 territories in built-up areas (21.4 %), 11 on the border of built-up and forested areas (26.2 %), 6 (14.3 %) on the border of built-up and arable areas and only three territories (7.1 %) located mainly in the grassy pans (fig. 3).
The number of coraciiform species recorded in the riparian forest near Katima Mulilo appears to be very high (N = 13), probably one of the highest in southern Africa. It should also be mentioned that in close proximity to the study area, a large colony (c 500 nests in 2016) of the Southern Carmine bee-eater Merops nubicoides, c. 50 pairs of the white-fronted bee-eater and a few pairs of the swallow-tailed bee-eater Merops hirundineus have been recorded (Kopij, 2018a). In the neighbouring town of Katima Mulilo, well-endowed with indigenous and exotic trees (highly modified riparian forest), the number of coraciiform species was nine (Kopij, 2016); in the Kalahari woodland (12 km long transect) in the same Zambezi Region – also nine (Kopij, 2017), in Kasane on Chobe River – five (Kopij, 2018c). Outside the Zambezi Region the number of coraciiform species was much lower, e.g. in urbanized areas in the north central Namibia it was four (Kopij, 2014); in Bloemfontein it as also four (Kopij, 2001a, 2015), in Roma Valley, Lesotho – three (Kopij, 2001b), in Swakopmund on Atlantic coast – none (Kopij, 2018b).
To date, few data have been published on the population densities of coraciiform birds in Africa (Hockey et al., 2005). For the lilac-breasted roller the highest density was recorded in Mababe Depression in the Chobe National Park, Botswana (Herremans, 1997). However, the density varied considerably even within the same year. For example, in N and E Botswana, it was highest in Aug/Oct (10 birds/100 km), and lowest in Nov./Dec. (2.5 birds/100 km) (Herremans and Herremans-Tonnoeyr, 1994). The little bee-eater nested at a density of two pairs/100 ha in broad-leaved woodland in the Limpopo Province, South Africa (Tarbotton et al., 1987). Kopij (1999, 2001a, 2015) recorded 32 African hoopoe breeding pairs (i.e. 0.6 pairs/100 ha) and 3 scimitar-billed wood-hoopoe breeding pairs (i.e. 0.1 pairs/100 ha) in 5,000 ha of urbanized, well-timbered habitats of Bloemfontein, South Africa (Kopi,j 2001a, 2015). High species diversity and population densities of coraciiform species recorded in riparian forest indicate that this vegetation, even if partly modified by human activities, may play a very important role in the protection of these species, which can be regarded as indicators of a high level of biodiversity. Protection of any remaining stretches of this rich and unique forest vegetation along the Zambezi River should be among the highest conservation priorities in Namibia.