Age Differences in Home Range and Site Fidelity of Black-Necked Cranes Grus nigricollia Born in Yanchiwan,Gansu
[Objectives]Site fidelity,defined as the return to and reuse of a previously occupied location,is a common behavior observed in many species.Factors influencing site fidelity include gender,age,season,among others.The Black-necked Crane Grus nigricollia,a first-level protected species in China,holds significant ecological and cultural value.Yanchiwan,located in the northern foothills of the Qilian Mountains in Gansu Province,serves as an important breeding and summering site for these cranes,marking the northernmost boundary of their known breeding range.Research on Black-necked Cranes in this region is crucial for their conservation.This study aims to investigate the differences in home range sizes among cranes of different ages during the summering and wintering periods,with a particular focus on the site fidelity of individuals born in Yanchiwan.[Methods]From 2018 to 2020,we captured juvenile Black-necked Cranes and fitted them with rings and satellite trackers.Individuals tracked for more than two summering periods were selected for analysis.Tracking data were filtered based on factors such as time,instantaneous speed,and accuracy.Kernel density estimation(KDE)methods were used to calculate the home range and core area for cranes of different ages during the summering and wintering periods use the"amt"package in R v.4.2.3.The degree of home range overlap among different age groups was also assessed.Logarithmic transformations were applied to the home range and core area data,followed by differential tests.Statistical analyses were conducted using Student's t test and Mann-Whitney U test,and QGIS was used for mapping.[Results]A total of 18 individuals were tracked over more than two summering periods.Juveniles exhibited smaller home range and core area compared to subadults during both summering and wintering periods(home range in summering period:t=-2.37,df=28,P=0.025;core area in summering period:t=-2.19,df=28,P=0.037;home range in wintering period:W=128,P=0.011;core area in wintering period:W=110,P=0.003).The largest home range and core area were observed in 1-year old individuals,but no significant differences were found between 1-year old and 2-year old subadults(Fig.1).The degree of home range overlap did not significantly differ across age stages(P＞0.05).Notably,33.33％of the 1-year old subadults did not return to their birthplace(n=6)(Fig.2),and one individual was recorded summering in Mongolia(Fig.3).Additionally,Black-necked Cranes exhibited higher habitat fidelity during the wintering period across all age groups(Fig.4).[Conclusion]This study demonstrates that Black-necked Cranes born in Yanchiwan exhibit marked exploratory behavior during the subadult stage,providing insights into the movement patterns of subadult cranes originating from this region.The findings underscore the critical role of the Yanchiwan breeding population in the overall population dynamics of Black-necked Cranes and highlight the significance of subadults in population dispersal.These results offer valuable information for understanding the contributions of the Yanchiwan breeding site to the broader conservation and management strategies for Black-necked Cranes.
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