How Wintering Habitat Structure Affects Number And Distribution Of Black-necked Cranes(Grus Nigricollis):A Case In Xundian Mountains

Habitat,as a living geographical space,provides Black-necked cranes(Grus nigricollis)with the necessary resources for their life activities,and plays a vital role in their survival,reproduction and population development.To explore the relationship between habitat structure and Black-necked crane is of great significance for effective protection of Black-necked crane.Based on remote sensing and geographic information technology and field investigation,the relationship between habitat structure and the number and distribution of Black-necked cranes was studied,and the mechanism of habitat structure affecting the number and distribution of Black-necked cranes was analyzed.The results are as follows.(1)Since 1994,the overwintering Black-necked Crane population in Xundian has shown a trend of sharp decline first and then slow rise,It has recently maintained at about 50 cranes and tended to be stable,but its distribution range has contracted to the mountain area centered on the remaining marsh meadow.By comparing the habitat structure of four spatial levels:the current distribution area,the former distribution area,the Xundian Nature Reserve and the comprehensive conservation area,it was found that the proportion of swamp meadow and water area in the current distribution area of Black-necked Crane increased,the proportion of woodland decreased significantly,and the cultivated land became the dominant landscape.Landscape heterogeneity has increased,and the connectivity between different types of landscape is relatively high,showing a variety of habitats interconnected,mosaic landscape structure.In terms of time,compared with 1990,the characteristics of the habitat structure in 2018 are the decrease of the proportion of swamp meadow and cultivated land,the increase of the proportion of woodland,the increase of landscape fragmentation and the decrease of connectivity.As a result,the number of overwintering Black-necked cranes declined dramatically.(2)The preferred habitat structure of overwintering Black-necked crane is a landscape complex with low proportion of forest and construction land,high proportion of marsh wetland and cultivated land,and interconnected habitat elements.The number of Black-necked cranes was positively correlated with the proportion of swamp meadow and landscape complexity(P<0.01).The larger the proportion of swamp meadow,the more irregular the patch shape,the better the survival of Black-necked cranes.The proportion of forest land was negatively correlated with the number of Black-necked cranes(P<0.01).The bigger the proportion of forest land was,the worse the survival of Black-necked cranes was.The proportion of water and cultivated land had no significant effect on the number of Black-necked cranes.(3)Food availability is one of the important factors affecting the number and distribution of Black-necked cranes.The overwintering food of Black-necked Crane in Xundian Nature Reserve is mainly plant food such as potato,vine and radish,supplemented by animal food such as insects and fish.A large amount of vegetable food is stored in cultivated land,5.2n/m2 or 303.7g/m2.Shrub grassland stored mostly animal food,18.6n/m2 or 33.8g/m2,while shrub land had less food.The availability of food indicated by soil compactness showed that the availability of food in different habitats was cultivated land>swamp meadow>shrub land>shrub grassland>woodland.The soil of cultivated land is the most soft,and the difference between cultivated land and swamp meadow,shrub grassland,shrub land and woodland is very significant(P<0.01),followed by swamp meadow,which is very significant with other types(P<0.01).Food availability is highest in cultivated land and lowest in forest,which explains that Black-necked cranes are mostly distributed in cultivated land but not in forest.(4)Habitat convenience is another important factor affecting the habitat selection of Black-necked cranes.During overwintering,the predominant daytime behaviors of Black-necked cranes were foraging and resting,accounting for(60.9+7.2)%and(19.5+3.7)%of the total day,respectively.The predatory behavior of Black-necked cranes was the most in cultivated land habitats,accounting for(36.8+7.4)%.Break behavior mostly occurred in cultivated land and swamp meadow,accounting for(8.4 +3.0)%and(7.1+2.7)%respectively.The cultivated land has abundant food storage,flat and open terrain,which makes it easy for Black-necked cranes to be alert and move in the process of foraging to avoid harmful interference.The concealment and water source of swamp meadow provide an ideal noon rest place for Black-necked cranes.Therefore,the high convenience of cultivated land and swamp meadow prompted Black-necked cranes to prefer these two habitats.(5)The habitats of the reserve are mainly confronted with various disturbances,and the farmer's work on cultivated land is the main disturbance.The cultivated land is rich in food storage,which is the habitat type with the highest utilization rate of Black-necked crane.Therefore,Black-necked cranes have considerable tolerance to interference in order to obtain the necessary food for overwintering.Therefore,the preferred habitat structure of overwintering Black-necked crane is a landscape complex with low proportion of forest and construction land,high proportion of swamp wetland and cultivated land,and interconnected habitat elements.Habitat food availability,convenience and harvesting disturbance comprehensively affect the habitat selection of overwintering Black-necked cranes,and food has the strongest impact.Black-necked cranes have considerable tolerance to interference in order to obtain food.