| The avian mixed-species flock is a form of organization in which two or more species of birds form a close group and forage together,and it is also an important social structure.There are two hypotheses about the function of the mixed-species flock:improving the foraging efficiency of the group and reducing the probability of the individual being prayed.This study conducted a three-month survey of the Meihuashan National Nature Reserve in Fujian Province in the winter of 2020～2021.28 transects were set on the four altitude gradients of the study area to explore characteristics of the structural composition,members’ roles,mixing behavior and inter-species relationships of the avian mixed-species flocks in this area,and to compare the effects of biological factors and non-biological factors on these variables.During the investigation,a total of 576 mixed-species flocks were recorded,including 39 species and 12,085 individuals of birds.These flocks distributed in an altitude range of 400～1599 m,and in three habitat types:coniferous and broad-leaved mixed forest,broad-leaved forest and bamboo forest.The three dimensions of species richness,size and number of activity layers reflect the structure of the mixed-species flocks.The wintering mixed-species flocks in Meihuashan have average 3.75±2.06 species and 20.98±15.78 individuals.The mixed-species activities involve five layers of the vertical structure of the forest,and the canopy class and understory are the main ones.The species composition of the flocks is dominated by Passerines.All the members are local resident or winter migratory birds.The principal members with a frequency of occurrence more than 5.00%and the number more than 50 are as followed:Grey-cheeked Fulvetta(Alcippe morrisonia),White-bellied Erpornis(Erpornis zantholeuca),Pallas’s Leaf Warbler(Phylloscopus proregulus),Rufous-faced Warbler(Abroscopus albogularis),Chestnut Bulbul(Hemixos castanonotus),Yellow-browed Warbler(Phylloscopus inornatus),Yellow-cheeked Tit(Machlolophus spilonotus),Black-throated Bushtit(Aegithalos concinnus),Japanese White-eye(Zosterops japonicus),Mountain Bulbul(Ixos mcclellandii),Rufous-capped Babbler(Cyanoderma ruficeps),Fork-tailed Sunbird(Aethopyga christinae),Grey-chinned Minivet(Pericrocotus solaris),Orange-bellied Leafbird(Chloropsis hardwickii)and Streak-breasted Scimitar Babbler(Pomatorhinus ruficollis).The role of members in the mixed-species flocks can be divided into nuclear species,follower species and rare species.The frequency of occurrence of the Greycheeked Fulvetta is as high as 52.43%,the total number is 4926,and the frequency as the nuclear species is as high as 98.01%.So,Grey-cheeked Fulvetta is the dominant species in the mixed-species flocks and the typical nuclear species occupying an absolute leading position.Pallas’s Leaf Warbler,White-bellied Erpornis,Rufous-faced Warbler,Yellow-browed Warbler and Yellow-cheeked Tit have a higher frequency of occurrence and a higher total number while they are all typical follower species.The results of the survey found that the number,size and species richness of avian mixedspecies flocks formed a certain trend with the time of the day,forming two peaks at 8:30-11:29 and 14:30-15:29.Altitude gradients have significant impact on the structure of the flocks through temperature and food resources.The structure at 400～699 m is the simplest compared to the altitude above 700 m.Vegetation types also have a significant impact on it through the available food resources and spatial utilization:the structure of bamboo forests is obviously simpler than that of mixed coniferous and broad-leaved forests and broad-leaved forest.In these flocks,the principal members have their own characteristics in behavior,activity layers and intraspecies size.The flock led by the typical nuclear species also shows significant differences between species.Through the participation in the flocks,the 15 principal members were classified by sociality and interspecies association respectively,and found that they have different mixing intensity and combination preferences.Though the mixing participation and behavior characteristics of the principal members,it is found that Grey-cheeked Fulvetta plays an important role in the mixed-species flock.This study preliminarily verified the functional hypothesis of the mixed-species flocks through the typical ity of the nuclear species:the mixing characteristics of Grey-cheeked Fulvetta can promote the formation of flocks,provide group cohesion,act as information transmitter and predator-watcher,and improve foraging efficiency while increasing vigilance. |
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