山地次生林长耳鴞对喜鹊巢址的利用

Occupation of Magpie's Nest Sites by Long-eared Owls in Secondary Forest

1996年至 1 998年夏季 ,在左家自然保护区对长耳 ( Aiso otus)的巢位及巢树进行了系统观察和初步研究。结果表明 :喜鹊 ( Pica pica)巢址是长耳选择巢位的重要资源 ,占发现总巢数的 83%。在长耳所利用的 2 0棵喜鹊巢树中 ,蒙古栎 ( Quercusmongolica)所占的比例最大。喜鹊巢树的树种、胸径、及其附近的灌木数量等生态因子是该巢址能否被长耳所利用的重要生态指标。被长耳所利用的喜鹊巢址距农田的距离与那些未被利用的巢址差异显著。

We studied nest sites and nest tree characteristics of Long-eared Owls (Asio otus) in Zuojia Nature Reserve of Jilin Province,China.Our study sites,42km 2,were distributed in middle of Jilin Province (126°0′~126°1′N,44°6′~45°2′E),which was located on hill extending from eastern Changbai Mountain to western plain,ranging from 200m to 500m above sea level.The climate was east monsoon climate,characterized hot,dry summers and cold,snowy winters.The two dominant vegetation types present on the study area were deciduous broad-leaved forests and artificial coniferous forests. We located nest site using procedure described by Ganey (1994).Once owls were located during night-time surveys,one of the adults was fed mice and followed to the nest as it delivered the prey to either an incubating/brooding female or nestling.If Magpie's nests were occupied by Long-eared Owls there would have no “lid” on the upper nests.We recorded information on five variables to describe each nest tree,of which we present data on the three most important measurements.In order to comparing analyses we climbed 40 nest trees (20 for Long-eared Owls' and 20 for Magpie's) to measure nest characteristics.Detailed vegetation information was obtained from 20 nest stands to quantify differences between habitat used for nesting and unused Magpie's nest site. Long-eared Owl nests were loacated in four tree species.Seventy percent were located in Mongolian Oak (Quercus mongolic),15% in Scoth Pine (Pinus syvestris,10% in Dahurian Birchs (Betula davurica),and 5% in Davids European Aspen (Populus davidiana).We found no significant difference in nest tree height (t 18 =-0.44,p=0.67) ,nest tree age (t 18 =0.21,p=0.84),nest height (t 18 =-4.29,p=0.02) between occupied and unoccupied nest tree.However,there are significant differences in nest tree dbh (P<0.01),and external diameters of the nests (P<0.01).We measured 86 vegetation varables at 246 sample points in 40 nest stands.We reduced the original 86 variables at 20 by eliminating variables whose frequency of occurrence was too limited to be useful in the analyes and by removing variables which were highly correlated with other variables.Because transformation resulted in little or no improvement,we used untransformed variables in all analyses.The difference of most habitat characteristics between occupied and unoccupied nest sites were insignificant except for variables including tree dbh,Shrub%,Shurb richness and Nfd.Those of nest sites were occupied by Long-eared Owls had less Shrub%,lower Shrub richness,and shorter distance form farmland to the nest sites.Five variables used for Stepwise DA to differentiate occupied nest stands from those unoccupied were tree dbh,Shrbu%,Nfd,Level3,and Grass%.The results showed that the standized canoncal discriminant funtion coefficients of the five important variables were -0.719 (Tree DBH),0.693 (Shrub%),0.691(Nfd),0.446(Level3),and -0.421(Grass%).In the firest two steps of the analysis,Wilks' Lambda were 0.657 and 0.613 which had great contribution to differentiation of the two groups.The firest eigenvalue of canonical discriminant function was 3.39.Over 75% of all sample points combined were correctly classified by discriminant models.