| Nest-tree,the direct attachment of bird nests,are so great significance for bird breeding that plays a role in directly supporting nests,providing concealment,and determining the height,concealment and environmental conditions of nests.As one of national second-class protected birds,Red-Billed Leiothrix(Leiothrix lutea)is also the Provincial bird of Hunan Province,which own high ornamental and ecological value,and its field population had been in a declining tendency for a long time.There is also a lack of research on the nest-tree selection and mechanism of this species.To try a in-depth explore on nest-tree selected preference and its influence on breeding fate about Red-Billed Leiothrix,this study surveyed systemly on species composition and selection preference of nest-trees,the relationship between nest concealment and breeding fates,and the influence of nest-tree selection factors for Red-Billed Leiothrix in 12 fixed line transects at Liuyang Daweishan Nature Reserve(DSNR),Hunan Province,during 2019 to 2021.The main results are as follows:(1)Nest-tree selection preference:A total of 266 potential nest-tree species,belonging to 117 genera and 63 families,were recorded in breeding area of Red-Billed Leiothrix at Dawei Mountain Reserve during the study.There were 185 nests built in 190 nest-trees,involving 39 genera of 24 families,accounting for 19.92%of potential tree species in 3 breeding seasons,and only some of nest-trees were used to nests simultaneously Red-Billed Leiothrix showed a significant preference for nest trees and their life-forms,especially,among shrubs and bamboos species of Hunan Yushan bamboo(Yushania farinosa),Huakwood(Stephanandra chinensis)and Japanese sandalwood(Symplocos Nest-tree species were classified by selection frequency,with moderate selection by 10%>frequency>2%,and low selection by 2%>frequency>0.According to One-way ANOVA analysis,selection frequency of nest trees was extremely significant difference within life-forms(F=39.95,df=4,P<0.01),and selection frequency of nest-trees was extremely significant difference within levels of selection(F=237.59,df=2,P<0.01).In addition,nest-tree selection varied along different altitude,with a significant decrease in nest-tree diversity with elevating altitude(y=-6.264x+68.916,R2=0.7103).(2)Nest-site concealment and breeding fate:Leiothrix lutea differed in their need for concealment in different orientations,preferring nest-sites with higher concealment above the nest(Mean=63.14%± 1.65%)and around the nest(Mean=51.89%±1.53%)and lower concealment below the nest(Mean=20.62±1.01%).The combined nest concealment index was 45.23%± 1.65%.There were 170 of the 185 nests had a clear breeding outcome,in which 61 nests breed successfully and 109 nests breed unsuccessfully,giving a breeding success rate of 35.88%.In addition,the nest tree selection of Red-Billed Leiothrix did not differ significantly between years and differed between altitudes,and nest tree diversity tended to decrease significantly with increasing altitude(y=0.6131x+18.499,R2=0.3133).(3)Influencing factors of nest-tree selection:A principal components analysis was carried out based on eight nest-site variables from 122 randomly measured nest-trees utilized in the breeding area versus control trees for two breeding periods of Red-Billed Leiothrix from 2020 to 2021.The results showed that the variance of the first principal component contributed 31.27%,including tree height(TRH,0.470),nest height(CNH,0.490)and the first branch height(TFBH,0.562)getting the highest eigenvalues,which were all positively correlated with nest-tree selection of Red-Billed Leiothrix.Posteriorly,the variance of second principal component contributed 27.56%,including concealment(HID,-0.438),shrub cover(SDS,0.468),tree height(TRH,-0.332),nest height(-0.361),number of nest branches(NEN,-0.382)and crown width(NEC,-0.313)were negatively correlated with nest-tree selection of Red-Billed Leiothrix.But the distance from the road(DRF,0.301)was positively correlated with nest-tree selection of Red-Billed Leiothrix.(4)Nest-tree selection models:Among eight nest-site variables measured,five variables were found to be extremely significant difference each other,including nest integrated concealment(HID),nest tree crown width(NEC),shrub cover(SDS),nest-tree first branch height(TFBH)and nest branch number(NBN).These five variables were used to construct 32 nest-tree selection models,including the Global model and the Null model.A total of two models were considered as candidates for the optimal model according to the criterion of Δ AICc<2,and the cumulative weight of the models(Cum.Wi)reached 0.98;among them,the model constructed by nest integrated concealment(HID)+shrub cover(SDS)+nest-tree crown width(NEC)+nest-tree first branch height(TFBH）+ number of nest-tree branches(NBN)was the optimal model,which was compared with the other candidate models.The results of model average analysis showed that nest concealment,shrub cover and nest-tree branch height had positive effects on nest-tree selection,while nest-tree first branch height had negative effects on nest-tree selection.The present study systematically investigated nest-tree selection and mechanisms in Red-Billed Leiothrix and showed that the species had a significant preference for nest-trees,providing new insights into the influence of nest-tree variables on this species.In this study,the ’nest concealment’ hypothesis was able to explain the nest-tree preference of Red-Billed Leiothrix,and the ’adaptive peak’ hypothesis also had some explanatory quantity.The results may provide a scientific basis for the conservation and restoration of regional breeding habitats of Red-Billed Leiothrix. |
