A Study On The Mixed-Species Flock In Mangrove Reserve Of Beilun Estuary

The mixed-species flock in mangrove reserve of Beilun estuary was studied fromOctober 2005 to December 2006. Five aspects about mixed-species flock were includedin the survey: social group type and species composition,foraging behaviour andinterspecific competition,social roles within the flock,hostile interactions,responses ofmixed-species flock to predator. The main results have been showed blew:1,115 bird species, belonging 33 families 8 orders were recorded during the studyperiod in the study area. Among them, 57 species are resident, 11 species are summermigrant, 45 species are winter migrant and 2 species are passenger. Among the 115species, 57 species are forest birds, 58 species are water birds, the ratio of the former isequal to the latter.2,In the social group type, the species of water birds and forest birds thatbelonged to the solitary individual accounted for the low proportion(16.7%) in theircommunities, respectively. They also showed the tendency that they would never join inthe mixed-species flock. The water birds Common Sandpiper Actitis hypoleucos,ChineseLittle Bittern Ixobrychus sinensis,Little Heron Butorides striatus and the forest birdsSpotted Munia Lonchura punctulata,Richard' s Pipit Anthus hodgsoni,Olive-backedPipit Anthus hodgsoni,Red collared Dove Streptopelia tranquebarica,Spotted DoveStreptopelia chinensis also would not appear in the mixed-species flocks, the solitaryindividual type and the single-species flock type were their only two flocking behaviour.In the single-species flock, the individuals of the maximal proportion were two inmost species. The winter migrants in the wetland showed the highest tendency to join the mixed-species flock, and the tendency existed the significantdifferences in different season. The forest birds' mixed-species flocking behaviour didnot exist the differences in different season. The correlation between the species and theindividuals in the mixed-species flock were significant different, with the exception ofwinter mixed-species flock.3,During the winter, the species in mixed-species flock would extend their nichebreadth of foraging behaviour in different extent. The species that have the similarecology requirement can tolerate the niche overlap. They could avoid the strongcompetition through the different foraging strategies.4,In the mixed-species flock of water birds, the Little Egret Egretta garzettabelonged to the Autumn "nuclear species", but its nuclear status had been replaced bythe winter migrant Dunlin Calidris alpine during the winter. The familiar species ofSnipes in mixed-species belonged to the "follower species". The White Wagtail Motacillaalba,Yellow Wagtail Motacilla flava and Black-headed Gull Larus ridibundus belongedto the typical "joiner species".In the mixed-species of forest birds, the nuclear species would not change indifferent season. Great Tit Parus major and Yellow-browed Warbler Phylloscopusinornatus belonged to the "follower species", the species of "joiner species" were morethan other ones of social roles, they did not belonged to the fixed species. The function ofthe nuclear species can maintain flock cohesion and continuance.5,The hostile interaction in mixed-species flock can be divided into two types:interspecific and intraspecific. They are including supplanting attacks,chases fights. Thetimes of interspecific interactions were less than the ones of intraspecific interactions,much encounters occurred in the intraspecific species. Among interspecific interactions,much of them were the supplanting attacks; among intraspecific interactions, the ratioof chases fights was higher than supplanting attacks.6,Because of the existence of the mechanism of alarm calls and the "confusioneffect", the birds in the mixed-species flock can be more effective to avoid the predator's attack than the solitary individual. The mixed-species flock of waterbird will have the different reflections(running and flushing) to the different kinds ofjamming(walking and running), but the flections that the birds direct toward the 1person jamming and 2 person jamming had not the significant differences. The jammingof running were the easiest mode to result in the birds' alertness.7,Poaching,jamming in the beach,destroying forest to breed shrimp,poormanagement on wetlands are the important factors threatening the existence of thewater birds. In order to protect the water birds and wetland nature conservationeducation to the local public should be carried out and management of wetlands shouldbe strengthened in the near future.