| The red-crowned crane(Grus japonensis)is distributed in east Asia,and is one of the most endangered crane species in the world.There are two independent breeding populations of red-crowned cranes:the non-migratory population(the island population)in Hokkaido,northern Japan,and the migratory population in East Asia(northeast China,Russia).The migratory population mainly overwinters in the wetlands of the eastern coast of China and the Korean Peninsula.Yancheng National Nature Reserve(YNNR)is the most important wintering region for red-crowned crane.Red-crowned crane prefers natural wetlands dominant by common seepweed(Suaeda salsa).During recent decades,due to economic development,the land use types and intensities of YNNR have been changed significantly.Artificial development activities mainly including reclamation and the invasion of smooth cordgrass(Spartina alterniflora)have led to the degradation and loss of natural wetlands.Natural wetlands have been transformed into construction land,industrial land and agricultural land including farmland,aquaculture ponds and reed beds.Comparing to historic records,the distribution range of red-crowned crane has significantly declined,and they are now concentrated in the natural wetland dominated by common seepweed in the core zone and surrounding areas of the YNNR.Farmland,aquaculture ponds and artificial reed beds have become important habitats for red-crowned crane.The red-crowned crane gradually uses artificial and semi-artificial wetlands as alternative habitats,which are influenced by human disturbance and habitat changes caused by various agricultural activities.However,few studies have focused on red-crowned cranes use of agricultural habitats and their adaptation to the interference of various agricultural activities and environmental changes.The response of the wintering red-crowned crane to the change in the agricultural activities in the artificial habitat is very important for the scientific management and population protection of the red-crowned crane in the YNNR.During the wintering period of 2017-2019,by continuous monitoring of agricultural activities and red-crowned crane population in the YNNR,temporal and spatial patterns of the overwintering population and habitat distribution of red-crowned crane were studied.The environmental factors affecting the habitat utilization of cranes were quantified.The response of cranes to human management activities in the habitat was analyzed.The main results were as follows:(1)During 2003 to 2018,the area of natural wetland in YNNR and its surrounding areas continued to decline.Meanwhile,the area of artificial habitat mainly composed of farmland and aquaculture ponds continued to increase,which has become the main type of artificial habitat in this area.Agricultural activities related to land use types include planting,aquaculture,reed harvesting and salt production.Accordingly,farmland,aquaculture pond,artificially managed reed pond and salt ponds are the main types of land use for agricultural.During winter,agricultural activities changed the environment of artificial habitats,in which the area of rice stubble fields(47199±299 hm~2,91%of the total area of farmland)gradually decreased because of being turned into wheat fields.Water level of aquaculture ponds decreased significantly due to harvest of aquatic product.(2)In YNNR,the population of the wintering red-crowned crane kept relatively stable during the study period.Compared to historical data,the population of the crane showed an upward trend during 1982-1999,and gradually decreased to a population size of 400-600individuals after 2000.The core zone was a concentrated area for red crowned cranes.However,the population and relative abundance of crane in the experimental zone and buffer zone showed a decreasing trend.The habitat types of red-crowned crane during the winter included common seepweed tidal flats,reed ponds,farmland,aquaculture ponds,reservoirs,restoration area and artificial feeding site.The priority habitats of cranes changed during the entire wintering season.Artificial habitats provided important habitats for the cranes.During the whole wintering period,common seepweed tidal flats were preferred by red-crowned crane.In November and December,cranes preferred farmland in the buffer zone,and then altered to use the common seepweed tidal flats in the core zone.Red-crowned crane showed negative selectivity to aquaculture ponds.The Aquaculture ponds could only provide compensating habitat for cranes(relative abundance 5.8%-11.0%).The average group size of red-crowned crane was(6.2±0.8),and cranes appeared most frequently in family group.The average group size of red-crowned crane in farmland was the largest,followed by common seepweed tidal flats.The average group sizes were significant different among habitat types.(3)Although the artificial habitats could provide habitat for the red-crowned cranes in winter,the environmental factors of the artificial habitat still restricted the habitat availability for the cranes.The change of habitat type caused by human management activities(ploughing and wheat planting)in the farmland of the buffer zone during the growth cycle led to the decrease of crane abundance in rice stubble fields.Cranes avoided the fallow fields,and mainly used wheat fields as their habitats after ploughing.Different buffer zones and habitat types had significant influence on the abundance of crane in farmland.All the factors including sub-field size(the farmland was divided into several sub-fields according to the inherent ridge),distance to the natural wetland,distance to the road,distance to the residential area and the existence of common crane(G.grus)impacted crane abundance in the rice stubble fields,while the main habitat factors affecting the crane abundance in the wheat field were the existence of common crane,the distance to the road and sub-field size.The human disturbance in the growth cycle of farmland in the reserve directly and indirectly(by changing habitat type)influenced the abundance of cranes.(4)During the wintering periods,the red-crowned crane mainly used the aquaculture ponds in the buffer zone of the reserve.There were no significant differences of the population number among three wintering periods.Five factors including water depth,species abundance,species richness,structures and distance to road were identified as influence factors affecting the aquaculture ponds use by cranes.No significant relationships between pond characteristics and crane abundance were found.All the factors influenced the use of ponds by cranes.However,crane occurrence was significantly associated with only water depth.Cranes avoided the pond with water deeper than 20 cm.Agricultural activities in the artificial habitat changed the temporal and spatial distribution patterns of red-crowned cranes,and the cranes showed adaptive responses to the artificial habitat.The agricultural activities in the artificial habitat changed the habitat conditions,resulting in the change of crane utilization patterns accordingly.Long-term,comprehensive and detailed investigations on the number and distribution of the red-crowned crane,as well as the determination of its main wintering gathering areas,was important for effective protection of crane population and its habitats.According to the response of cranes to agricultural activities,effective measures of habitat management were necessary.More specifically,appropriate management practices to benefit wintering cranes included keeping a large area of rice stubble farmland in the area far away from the residential area and close to the natural wetland,and keeping a low water level(lower than 20 cm)as long as possible after the harvest of aquaculture ponds in the buffer zone.In order to reduce the impact of human disturbance on the habitat utilization of red-crowned crane,the control of human disturbance in agricultural habitat should be strengthened.These management measures were very important to maintain and restore the population and habitat of red-crowned cranes in the YNNR. |
PDF Full Text Request