影响灰脸■鹰巢址选择的主要生态因素

The important ecological factors influencing nest-site selection of grey-faced Buzzard Eagle

1996～ 1 997年 ,在吉林省左家自然保护区及土门岭地带对灰脸鹰 ( Butastur indicus)的巢树和巢址特点进行了系统研究。运用逐步判别分析的方法 ,通过对因子进入判别方程的先后顺序检测因子的重要性 ,通过对 Wilk'sλ值的检测确定各因子对判别模型的贡献率 ,根据生态因子的重要性和贡献率大小确定影响灰脸鹰巢址选择的主要生态因素。两年共观测灰脸鹰的巢址 1 2处 ,其中 83.3% ( n=1 0 )位于山坡的上部位置 ,66.7% ( n=8)位于山北坡 ;在灰脸鹰所利用的巢树中 ,松科 ( Pinaceae)植物占的比例最大 ,为 75 % ( n=9)。逐步判别分析结果表明 ,胸径大于 30 cm乔木的基面积。

The habitats of Grey faced Buzzard Eagle ( Butastur indicus ) have decreased seriously because of the timber production and farmland reclamation in recent years. An understanding of the nest site selection of this bird is particularly important for its conservation. We studied nest site selection of Grey faced Buzzards( Butastur indicus )in Zuojia Natural Reserve from March to September, 1996～1997. In this paper we describe the nest and roost characteristics of this raptor in northeastern China. Our null hypotheses were: (1) no difference exists between nesting site and random habitat distributed throughout the study area; (2) no difference exists between nest site and general habitat within nest stands. The study area, approximately 84km2 in size, was located in Zuojia Natural Protection Area and included the Tumengling Mountains and Zhujia Mountains ranging from the eastern ChangBai Mountains to the western plain (126°1′～127°2′ N, 44°6′～45°5′E).Elevation at the site ranged from 200m to 500m above sea level. The climate is east monsoon, characterized by hot, dry summers and cold, snowy winters. The vegetation within the study area was quite diverse, although the forest type is only secondary forest. We measured site characteristics in sample plots centered below eagle nests and roosts and at random locations in forest habitat. Detailed vegetation information was obtained from 12 nest stands to quantify difference between habitat used for nesting and unsuitable habitat. Nesting habitat data were collected four sample points 25m from each nest in each cardinal direction. Four sample points were located in each cardinal direction and at a random distance from the nest tree to represent available habitat. This sampling was designed to address nest level habitat selection occurring within a hypothetical Grey faced Buzzard Eagle home range. In each nest stand, four sample points were measured within both nesting and available habitat to increase the number of points available for use in the assessment of model stability. At each sample point information also was collected to provide a detailed description to the vegetation. We selected random forest plots throughout the study area by generating random universal transverse mercator coordinates, locating coordinates on the ground, then centering the plot on the nearest tree. Grey faced Buzzard Eagle nests were located in five tree species. Fifty percent ( n =6) of nests were located in Korean Larches, 25% ( n =3) were in Chinese Pines, and 8% each were in River Birch, Mongolian Oak, Manchurian Linden ( Tilia mandschurica ) respectively. Mean deviation of the nests in the trees was north westerly (mean aspect=342 5°, mean vector length=0.51, angular deviatio n =56 5°), but did not differ from a random distribution ( z =1 2, P <0 05). The distribution of random tree species differed from nest tree species ( X 2=8 9, d f =2, p <0 05). Nest trees were larger, denser, and taller than trees randomly located within the nest stand (Table 4). The distribution of forest types at nests differed from random sites ( X 2=15 62, d f =2, p <0 05), with most in the mixed conifer/river birch forest type. Position of nest sites on the slope differed from a random distribution ( X 2=11 26, d f =2, p <0 05). Eight nests (75%) were located on the upper third of the slope, three nests (19%) were located on the middle third, and one nest (6%) on the lower third. Mean slope aspect at nest sites was northerly (mean aspect=295°, mean vector length=0 37, angular deviatio n =56 5°), and differ significantly from random sites ( F =15 13, d f =1, 22, P <0 05). Nest plots differed from random plots (MANOVA; Wilks' Lambda=0 68, F =7 96, d f =8, 23, P <0 05). The t tests indicated that four of the 8 variables differed between nest and random plots (Table 2). Larger dbh, taller trees, greater canopy closure and greater basal area of mature trees best separated nest sites from random sites in th