Seasonal variations in the structure of avian community in Zambezi riparian forest

Among the different biomes in southern Africa, tropical riparian forests appear to be especially rich in terms of biodiversity, but little is known about avian communities occupying these forests. In this paper, bird counts were conducted in May, July/August, and October/ November in 2013 and 2014. The line transect method was used. A transect 16.6 km long was designed along the Zambezi River between S 17.4975 E 24.3478 and S 17.4874 E 24.4475. In total, 146 bird species were recorded. The number of species detected each season varied from 95 to 100. The number of dominant species was consistently low, varying between 2 and 3 depending on the month. However, the cumulative dominance and the dominance index were much higher in the dry season (May-August) than in the wet season (October-November). Two species were dominant each month: Euplectes axillaris and Pycnonotis tricolor. Vidua macroura and Estrilda astrild were dominant only in October, while Streptopelia capicola was dominant only in May. The group of subdominants was much more diverse than dominants and included 13 species. The Shannon diversity index increased between July and November from 3.45 to 4.05 but Simpson?s diversity index did not show any seasonal trend. Pielou?s evenness index was higher in the wet season (0.82-0.88) than in the dry season (0.76-0.79). The proportions of the main feeding guilds were much the same throughout the year, except for November, when the proportion of insectivores markedly increased, while that of granivores decreased. Riparian forest corridors in urbanized environments may be viewed as main instruments for offsetting the negative effects of habitat loss and fragmentation.

在南部非洲的不同生物群落中，热带河岸林在生物多样性方面尤为丰富，但人们对栖息于这些森林中的鸟类群落知之甚少。本文于2013年和2014年的5月、7/8月及10/11月开展了鸟类计数调查，采用样线法（line transect method）。沿赞比西河设计了一条长16.6 km的样线，范围介于南纬17.4975°东经24.3478°至南纬17.4874°东经24.4475°之间。共记录到146种鸟类，各季节检测到的物种数介于95至100种之间。优势物种数量始终较低，每月为2至3种不等。然而，累积优势度和优势度指数在旱季（5-8月）显著高于雨季（10-11月）。每月均有两种优势种：Euplectes axillaris和Pycnonotis tricolor；Vidua macroura与Estrilda astrild仅在10月占优势，而Streptopelia capicola仅在5月占优势。亚优势种组的多样性远高于优势种，包含13种。香农多样性指数（Shannon diversity index）从7月至11月由3.45升至4.05，但辛普森多样性指数（Simpson's diversity index）未呈现任何季节趋势。皮洛均匀度指数（Pielou's evenness index）在雨季（0.82-0.88）高于旱季（0.76-0.79）。主要取食功能群（feeding guilds）的比例全年基本一致，仅11月例外：此时食虫类比例显著增加，而食谷类比例下降。城市化环境中的河岸林廊道可被视为抵消栖息地丧失与破碎化负面影响的主要手段。