关键词: 黑颈鹤, 盐池湾, 筑巢栖息地, 人为干扰, 随机森林模型

Abstract

Aims: The black-necked crane (Grus nigricollis) is a flagship species of plateau and an important indicator of the health status of the plateau ecosystem. In recent years, plenty of research on black-necked cranes has been implemented, but these studies mainly focus on the migration, nest site selection, and foraging habitat selection of black-necked cranes. We know little about the preference of nesting habitat of black-necked cranes and the selection mechanism of nesting habitat. Black-necked cranes are divine birds in Tibetan Buddhism, and the species has always lived in harmony with the believers of Tibetan Buddhism. However, with the progression of human lifestyle, the problem of anthropogenic disturbance has become more prominent. Our research aims to provide a reference for understanding how black-necked cranes adapt to human modified habitats between multiple factors.

Methods: Nest sites and number of black-necked cranes were collected in Danghe Wetland from April to September in 2019 and 2020. Satellite interpretation was utilized to classify the habitats of the black-necked cranes. To study the distribution pattern of the nests and anthropogenic disturbance, we used nearest neighbor analysis and kernel density estimation. A random forest model was applied to explore nesting habitat selection mechanism of the black-necked cranes.

Results: There are two concentrated breeding grounds of black-necked crane nests in the Danghe Wetland and the nests are extremely concentrated. The two breeding grounds are located in the marsh in the north and south of the Danghe River. The houses of herders in the wetland are distributed in a strip on the gobi at the southern edge of the wetland. The density distribution of house is more concentrated on the south bank of the Danghe River, and the roads are also distributed along the south bank of the Danghe River. There is obvious geographical separation between the black-necked crane nests and anthropogenic disturbances. Meadows are the most prominent landscape type of wetland ecosystems and the sum of the proportions of marsh meadow and salinized meadow exceeds 50%. The proportion of shallow water marsh is relatively small, not exceeding 10% in two years. Deep water marsh and lake have smaller areas, below 3% and 2% respectively (average of two years). The distance from deep water marsh, shallow water marsh, and lake are the three critical environmental variables affecting the nesting habitat selection of the black-necked cranes, while the distance from houses and roads are less critical. The black-necked cranes prefer to nest in areas < 125 m from deep water marsh, < 130 m from shallow water marsh, and < 270 m from lake.

Conclusion: The deep water marsh, which the black-necked cranes strongly prefer when nesting in Danghe Wetland, is characterized by a relatively low percentage and clustered distribution. Meanwhile, the range of suitable habitat for the black-necked cranes to nest is narrow (< 125 m from deep water marsh, < 130 m from shallow water marsh, < 270 m from lake). Therefore, the breeding distribution of black-necked cranes is narrow. Resource factors are the main driving force for the distribution pattern of the black-necked crane nests. However, anthropogenic disturbance has little impact on nesting habitat selection. Therefore, the geographical separation between the black-necked crane nests distribution and anthropogenic disturbance is largely due to the preference for resources rather than avoiding disturbance. The habitat quality of the black necked-cranes in Danghe Wetland may decline, and the increase of livestock, multi-season utilization of pasture, and climate change may be the main reasons.

Key words: black-necked cranes, Yanchiwan, nesting habitat, anthropogenic disturbance, random forest model