Habitat selection across nested scales and home range assessments of the juvenile black-necked crane (Grus nigricollis) in the post-breeding period

Abstract

To know the details of the habitat selection and home range of black-necked cranes ( Grus nigricollis ) and how grazing influences them, we observed juvenile members of the population with satellite tracking in the Danghe wetland of the Yanchiwan National Nature Reserve in Gansu from 2018 to 2020 during the months of July–August. Population monitoring was also conducted during the same period. The home range was quantified with kernel density estimation methods. Then, we utilized remote sensing image interpretation with machine learning to identify different habitat types in the Danghe wetland. Manly’s selection ratios and random forest model were employed to assess habitat selection in home range scale and habitat scale. In the study area, a grazing restriction policy was implemented in 2019, and the response of Black-necked cranes suggest as follows: a) the number of young cranes increased from 23 to 50, which indicates a grazing regime affects cranes fitness; b) the current grazing regime does not affect the areas of home range and the selection of habitat types, but it affects the crane’s use of space as the mean overlap index of the home range was 1.39% ± 3.47% and 0.98% ± 4.15% in 2018 and 2020 years, respectively; c) there was an overall increasing trend in mean daily movement distance and instantaneous velocity indicate a movement ability increases of young cranes, and the ratio of disturbed cranes becomes greater; d) Human disturbance factors have little effect on habitat selection, and cranes are hardly affected by houses and roads currently. The cranes selected lakes, but comparing the home range and habitat scale selection, marsh, river and mountain range cannot be ignored. Therefore, we believe that continuing the grazing restriction policy will help to reduce the overlap of home ranges and subsequently reduce intraspecific competition, and then it increases the safety of movements of young cranes, and ultimately increases population fitness. Further, it is important to manage the water resources and maintain the existing distribution of roads and buildings throughout the wetlands.