Although forest gap ecology is an important field of study, research remains limited. By plot setting and point counted observation, the response of birds to forest gaps in winter as well as bird distribution patterns in forest gaps and intact canopies were studied in a north tropical monsoon forest of southwestern China from November 2011 to February 2012 in the Fangcheng Golden Camellia National Nature Reserve, Guangxi. The regression equation of bird species diversity to habitat factor was Y1=0.611＋0.002 X13＋0.043 X2＋0.002 X5-0.003 X8＋0.006 X10＋0.008 X1 and the regression equation of bird species dominance index to habitat factor was Y3=0.533＋0.001 X13＋0.019 X2＋0.002 3（3-0.017 X4＋0.002 X1. There were 45 bird species （2 orders and 13 families） recorded in the forest gap, accounting for 84.9% of all birds （n=45）, with an average of 9.6 species （range： 2-22）. Thirty-nine bird species （5 orders and 14 families） were recorded in non-gap areas, accounting for 73.6% of all birds （n=39）, with an average of 5.3 species （range： 1-12）. These results suggested that gap size, arbor average height （10 m from gap margin）, arbor quantity （10 m from gap margin）, shrub quantity （10 m from gap margin）, herbal average coverage （1 m from gap margin） and bare land ratio were the key forest gap factors that influenced bird diversities. On the whole, bird diversity in the forest gap was greater than in the intact canopy. Spatial distributions in the forest gaps were also observed in the bird community. Most birds foraged in the ＂middle＂ and ＂canopy＂ layers in the vertical stratification. In addition, ＂nearly from＂ and ＂close from＂ contained more birds in relation to horizontal stratification. Feeding niche differentiation was suggested as the main reason for these distribution patterns.
The limestone region in southwestern Guangxi contains the most typical karst landforms in the world. Due to their destruction, the original forests mainly survive in nature reserves in the form of fragmented areas. From June 2009 to September 2010 we conducted an investigation of 13 relatively isolated habitats or sites, selected from each of the 13 nature reserves in southwestern Guangxi, with the least amount of anthropological activity and the largest presence of the original vegetation, in order to study the distribution of birds on forest fragments. The distribution patterns of the birds and the factors which affect them were analyzed by using the 'BINMATNEST' software and the Spearman’s rank correlation analysis, to determine: 1) whether nested patterns of birds in the karst area of southwestern Guangxi exist or not and 2) which factors are correlated with the nested patterns and the effect of these factors on forming nested patterns. The results show that the birds had statistically significant nested patterns in the karst area and the specificity of the habitat of the birds had a significant effect on the nested patterns. We suggest possible reasons for these results, based on the characteristics of the seasonal tropical rain forests in the study area and on neutral theory. We also urgently recommend that close attention be paid to the protection of the diversity of the environment for birds in all fragmented habitats.
