北京地区同域分布的普通和黑头种群密度比较

2007年4月至7月,2007年12月至2008年1月,分别在北京市门头沟区小龙门森林公园、百花山自然保护区以及延庆县松山自然保护区,对同域分布的普通(Sitta europaea)和黑头(Sitta villosa)两种同域分布的类种群密度进行了调查。普通在小龙门森林公园、百花山自然保护区和松山自然保护区的种群密度分别是40.92、96.67只/km2和16.67只/km2。而黑头在上述3个调查区域的种群密度分别是2.03、16.67只/km2和23.33只/km2。普通的总体平均密度(51.4只/km2)高于黑头(20.68只/km2)。两种类分布的海拔和林型存在着差异。普通在海拔高度1070—1350 m的分布比较多。在海拔段1070—1250 m区间,普通的数量随海拔高度的增加呈递增的趋势。而黑头在海拔600—800 m分布较多,随着海拔高度的增加,种群数量呈递减趋势。普通主要分布在阔叶林和针阔混交林中,而黑头主要分布在针叶林中。

Comparison of population density in two sympatric nuthatch species

The land-use in Beijing is of special concern, with large forests being clearfelled, or turned over to logged forest, road and agriculture. These land uses are associated with declines in bird species richness or abundance and there is particular concern for the second cavity-nesting birds. Information on species distribution, population density, and key areas for protection is critical for biodiversity conservation. In secondary-cavity nesters, competition for nest cavity poses an important selective force determining the rate of reproductive success and population dynamic. Eurasian Nuthatch (Sitta europaea) and Chinese Nuthatch (Sitta villosa) are all second cavity-nesting birds, sympatric throughout many of the mountainous regions of Beijing. The densities of sympatric Eurasian Nuthatch and Chinese Nuthatch were investigated in Xiaolongmen Forest Park, Baihuashan Natural Reserve and Songshan Natural Reserve in Beijing from April to July, 2007 and December, 2007 to January, 2008.The line transect method was used to estimate bird densities. Transects were about 1.5 km long and walked at a speed of 1.5 km/h, only in dry conditions and when wind speed was not a hindrance to bird detection or activity. Horizontal perpendicular distance from transect to bird was recorded. All bird surveys began at dawn, when bird activity is usually highest. Transects were repeated on a different day in the reverse direction to minimize bias attributed to route direction and bird activity and time of day. Bird records from the two walks along each transect were pooled to calculate densities using Distance v. 5.0. All data were right-truncated at 50 m to remove anyoutlying records, improve model fit and reduce the likelihood of a bird encounter being assigned to an incorrect habitat type. We used one-way ANOVA to test the differences of the density of birds between locations, elevations and forest types.The density of Eurasian Nuthatch was 40.92 individual/km² in Xiaolongmen Forest Park, 96.67 individual/km² in Baihuashan Natural Reserve, and 16.67 individual/km² in Songshan Natural Reserve, respectively. However, the density of Chinese Nuthatch was 2.03 individual/km² in Xiaolongmen Forest Park, 36.67 individual/km² in Baihuashan Natural Reserve, and 23.33 individual/km² in Songshan Natural Reserve, respectively. The mean density of Eurasian Nuthatch (51.42 individual/km²) was higher than that of Chinese Nuthatch (20.68 individual/km²). There were differences in elevations and forest types between distribution models of the two nuthatches. Eurasian Nuthatch distributed more frequently in 1070-1450 m elevation. The number of individuals increased with elevation increasing. However, Chinese Nuthatch distributed more frequently in 600-800 m elevation and the number of individuals decreased with elevation increasing. The results showed both Eurasian Nuthatch and Chinese Nuthatch had selectivity to forest types. The numbers of Eurasian Nuthatch in broadleaf forest is 34 percent of the total number and the number in the broadleaf conifer mixed forest accounts for 30 percent;The number in Chinese pine forest only accounts for 18 percent. However, Chinese Nuthatch mainly distributes in conifer forest. The number of Chinese Nuthatch in Chinese pine forest is 78 percent of the total number and in broadleaf-coniferous mixed forest accounts for 22 percent. Eurasian Nuthatch occurred more frequently in broad-leaf forests and broad-leaf and conifer mixed forests, but Chinese Nuthatch mainly distributed in conifer forests. Eurasian Nuthatches in Beijing had higher population density than Chinese Nuthatches, owing to more suitable habitats.