Niche Differentiation Of Nesting Sites And Foraging Sites Of Mixed Breeding Herons

Objective:Niche differentiation is the result of mutual adaptation and adaptation environmental among species.It is particularly important to study the niche differentiation of species for understanding the origin of biodiversity and the mechanism of species coexistence.The nest is the environmental carrier of the breeding behavior of birds,and the suitable nest site can ensure the smooth progress of the breeding activities.Food is the basis and fundamental of living things,foraging sites is the important place for animals to obtain food resources.Ardeidae birds are typical mixed breeding birds,which use similar nesting sites and foraging sites resources and face high competition pressure during the breeding period.In order to reveal the coexistence mechanism of mixed breeding herons,we investigated the niche differentiation time dynamics of nesting space and foraging site niche differentiation of mixed breeding herons in Dali area of Yunnan Province.Methods:(1)In the spring and summer of 2012,2016 and 2021,the community structure and nest spatial distribution of breeding herons in Dali,Yunnan,China were investigated.The spatial niche of heron nests was divided into four dimensions,namely east-west horizontal direction,north-south horizontal direction,vertical direction and nest distance from the trunk.Then,the niche width values of heron nests were calculated based on Shannon-Wiener diversity index,and the niche overlap values of heron nests were calculated based on Schoener’s niche overlap index formula.(2)According to the characteristics of heron foraging activities in the Erhai Valley,three kinds of landscape foraging sites were set in this study,which were lakeside wetland landscape,artificial pond group wetland landscape,and farmland landscape.The number of foraging herons in the wetland landscape of lakeside and artificial pond group in Erhai was investigated month by month from May to September 2021,and the number of foraging herons in farmland landscape was investigated month by month from May to September 2022.Then,according to the foraging sites area of each landscape type and the species and the number of herons,the selection index of Bookhout was used to calculate and analyze the foraging sites preference of different herons and their temporal changes.Results:(1)In 2012 and 2016,the breeding heron community in Dali,Yunnan,China was composed of cattle egret(Bubulcus ibis),night heron(Nycticorax nycticorax)and little egret(Egretta garzetta),with the night heron being the dominant bird species.In 2021,intermediate egret(Ardea intermedia)was added to the breeding community,and cattle egret became the dominant bird species.(2)The nest density increased from 2016 to 2021,and the nest density of cattle egret increased significantly from 0.090/m~2to 0.252/m~2,while that of night heron and little egret decreased.By comparing the niche width values of cattle egret,night heron and little egret in 2016 and 2021,it was found that the niche of cattle egret was more generalized,while night heron and little egret were more specialized.The changes in niche overlap values of nest space indicated that the competition between cattle egret and night heron and little egret in 2021 was more intense than in 2016.(3)Cattle egret,little egret and intermediate egret used the three landscape foraging sites of lakeside wetland,artificial pond group wetland and farmland in Erhai during breeding period,but the utilization degree and preference types of foraging sites were different.Cattle egret and intermediate egret made the most use of farmland landscape,little egret made the most use of lakeside wetland landscape,and farmland was the preferred foraging landscape type of the three herons.(4)There were differences in herons foraging sites preferences at different rice growth stages:in the early stage of rice planting and growth,three heron species preferred farmland;In the late rice growth period,the lakeside wetland and artificial pond group wetland were the supplementary foraging ground for breeding herons.Conclusions:(1)In 2012,2016 and 2021,in the old town of Dali,cattle egret won the competition with the larger night heron.The dominant bird species changed from night heron to cattle egret,and the community structure and niche differentiation of breeding herons changed significantly.(2)The foraging sites differentiation at landscape scale showed that cattle egret and intermediate egret made the most use of farmland landscape,while little egret made the most use of lakeside wetland landscape,and farmland landscape was the preferred foraging site landscape type of the three heron species.