The Study On The Mixed-species Bird Flocks In Tiantong National Forest Park,Zhejiang Province

In order to understand the compositions and structures of the mixed-species flocks in Zhejiang Tiantong National Forest Park and explore the interspecific relationship and coexistence mechanism of the mixed-species bird flocks,we chose three forest types(coniferous forest,coniferous and broad-leaved mixed forest and evergreen broad-leaved forest)in Tiantong National Forest Park as the research objects and analyzed the characteristics of mixed-species flocks structures of different forest types from December 2015 to November 2016.With a variety of methods to measure the interspecific relationships among mixed-species bird flocks,we explored the function of nuclear species in maintaining and constructing the stability and cohesion of the mixed-species flocks.The study explained the coexistence mechanism of the mixed-species bird flocks in the Tiantong area.The results of the study are as follows:1.The composition of the birds faunaA total of 98 species were recorded in this survey,belonging to 13 subjects and 38 families.There are 65 Cynodon species,accounting for 66:3%of the total species.Non-beacon species accouting for 33.7%,mainly include alconiformes,Ciconiiformes,Charadriiformes,Gruiformes,and so on.According to the resident type,there were 47 resident birds(47.9%),15 summer resident birds(15.3%),18 winter migratory birds(18.3%)and 18 passing migrant birds(18.3%);According to the geographical area,there were 54 Oriental species(55.1%),37 species of Palaearctic species(37.8%),7 dispersed species(7.1%).2.The composition of the mixed-species bird flocksThe survey recorded a total of 197 mixed groups,including 34 species,7980 individuals(18 resident birds?7 passing migrant birds?5 winter bird?4 summer resident birds).All of the recorded mixed-species bird flocks are belong to the Passeriformes,total of 12 families.There are 7 Thrushidae,6 Pycnonotidae and 5 Turdidae were the most part in the mixed-species flocks.The mean species richness in mixed-species flocks is 4.42 ±1.37 and the mean flock size is 40.71 ± 12.88.In addition,the highest flocking frequency of the four species are:Grey-cheeked fulvetta(63%),Great tit(49%),Red-headed tit(45%)and Chestnut bulbul(38%).The main part of the mixed-species flocks in the Tiantong area is composed of the four bird species,as the the common species.3.The differences of the mixed-species flocks structure in three forest typesUnivariate analysis of variance showed that there were significant differences in the mixed-species flocks structure among different seasons(P<0.01)and there are significant differences in the mixed-species flocks structure of the three forest types in the same season(P<0.01).Seasonal variation and forest succession are the main factors to influence the structural differences of mixed-species flocks.In the three successional forests types,mixed forests held the most flocking species,individuals and species(coniferous and broad-leaved mixed forest>broad-leaved forest>coniferous forest).Compared with other regions,it was found that the mixed-species flocks of the Tiantong area,situated in Subtropical evergreen broadleaved forest contained fewer species,but the flock size is relatively larger,mainly determined by the number of common species.4.The mixed-species flocks type and nuclear speciesAccording to the mixed-species foraging flocks in the Tiantong area,the birds in the mixed-species flocks were divided into three fraging groups,namely shrub-users/SU,vertical-profile generalists/VPG and the canopy group.And then the mixed-species flocks are divided into two types:understory mixed-species flocks and canopy mixed-species flocks.The canopy mixed-species flocks mainly consists of vertical-profile generalists/VPG and canopy birds.Due to the lack of nuclear species,the flocking propensity was poor,easy to break down.The understory mixed-species flocks are mainly composed of the shrub-users/SU and the vertical-profile generalists/VPG.The Grey-cheeked fulvetta,the nuclear species and the leading species of the mixed-species flocks,maintaining the cohesion and stability of the mixed-species flocks.5.The interspecific relationship and coexistence mechanism of mixed-species flocksIn this study,the ?2 test-? correlation coefficient,Pearson correlation coefficient and niche index were used to measure the interspecific relationships among the mixed-species flocks in the three successional forests types.Positive relationship were in the mixed-species bird flocks and there was more significant positive correlations between Grey-cheeked fulvetta and the other species.Interspecific positive relationships indicate that species in mixed-species flocks share the same or similar resource requirements.That is also possible that one species created favorable conditions for another species.By calculating the niche breadth and overlapping values of the three dimensions,the results showed that the comprehensive niche breadth of the Grey-cheeked fulvetta was the largest.The wider of the attendant species niche were,the higher of the niche overlap would be.There are different niche overlaps and segregations between nuclaer species and attendant species.The species in the mixed-species flocks had less interspecific competition through niche differentiation and could achieve the stability and coexistence.The overlapping of attendant species and the nuclear species promoted the formation and stability of the mixed-species flocks.In addition,the hypothesis of "Predator avoidance hypothesis" and"Foraging efficiency hypothesis" were both suitable for our study area,and the latter dominated.