| Wintering ecology and migration strategies are important topic of avian ecology.Especially,behavior choice in wintering period and migration timing,flight speed and migration pattern are different among adults and juveniles,which are still poorly understood.Sanmenxia Reservoir Area is an important wintering ground for whooper swans,listed as the Second-Class National Protected bird species in China,and also the area with the highest wintering population density.225 whooper swans were captured in Sanmenxia Reservoir Area from 2014 to 2020,including 124 adults and 101 fledglings.The detailed wintering GPS locations and spring migration routes of each whooper swan were obtained by satellite tracking.Combined with the vegetation utilization and energy accumulation of swans with different age,we analyzed the home range size in different months of wintering period to understand the difference on winter ecology of adult and fledgling swans.Combining the date and number of swans departing the Sanmenxia Reservoir Area with the climatic factors to explore the difference on spring migration timing of swans with different ages.Fatherly,the different migration pattern of adult and sub-adult were found by analyzing the migration parameters including migration time and distance,straightness index,and number of stopovers.The results showed that the home range of swans increased first and then decreased,and the home range size of adult swans was always larger than fledglings.During wintering period,most of swans preferred to select in Sanmenxia Wetland Park,and some adults gradually dispersed from the Wetland Park along the upper reaches of the Yellow River to the Shengtian Lake,while some fledglings spread along the lower reaches of the Yellow River to the Pinglu Sanwan Wetland.With the arrival of spring migration,the swans in Shengtian Lake and Sanwan Wetland gradually returned to the Wetland Park.Adult swans departed firstly the Sanmenxia Reservoir Area,and were one week earlier than sub-adults.They all migrated to the northwest with the low wind speed and suitable temperature,and there was no significant correlation between migration angle and wind speed and direction.The effects of low temperature on the choice of migration date of adults were greater than that of sub-adults,resulting from higher efficiency of energy accumulation for adult swans at lower temperature.The spring migration of adults and sub-adults followed the pattern that longer migration distance with earlier migration timing,and shorter migration distance with later migration timing.Our results also showed that adults employed the energy maximum strategy during spring migration,which ensured that they had enough energy reserve when arriving at the breeding ground,which could better occupy high-quality breeding habitats and increase the breeding success.However,sub-adults employed shortest time strategy,which could ensure they reached the summering ground in the shortest time.The migration duration and speed were determined by the duration of stopovers.Hongjiannao and Ordos Relict Gull National Nature Reserve were the important stopover sites used by swans during spring migration.But a total of 88.9% of GPS locations at stopovers were not in the nature reserves,and the unprotected area proportion of adults was higher than sub-adults.Especially in Yumenkou Wetland and the middle and upper reaches of the Yellow River from Bayannur to Baotou in Inner Mongolia,where the nature reserves should be established as soon as possible. |
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