| Yanchiwan National Nature Reserve(YCW)is one of the main breeding areas of the Black-necked Crane(BNC,Grus nigricollis).Breeding ecology,including population dynamics,breeding pairs,breeding habitat selection,nest density,distance between neighboring nests,nest survival,reproductive success,and recruitment rate were investigated for BNC during 2013-2015.Numbers of BNC and breeding pairs remained relatively stable at around 140 individuals and 40 pairs.Recruitment rates ranged from 15.7% to 25.8%.29 nests were located during three years,including 24 haystack nests and 5 ground nests.Habitat type(ponds > marsh > riverine wetlands),disturbance(low > high)and water depth(deep > shallow)were the main factors that determined nest site selection of BNC.Average nest survival rate,hatching success,and breeding success of all 29 nests were 65.56 ± 5.09%,57.04 ± 6.12% and 32.78 ± 2.55%.Water depth,water body area,and distance to land were positively related to nest survival,while disturbance level showed a negative relationship.Biparental incubation model is an exquisite model to investigate how parents resolve sexual conflict and achieve cooperation especially in alpine cold environment.We used 24-hr-per-day video monitoring of 20 nests to systematically investigate incubation pattern of the BNC.Average nest attendance was 90.12%,with almost equal female and males nest attendance(45.35% vs 44.77%).The average length of incubation bout was 2.06 h with a frequent changeover pattern(10.87 times/per day)between parents and averagely 5.05 min duration.Males significantly spent more time getting the nest than did females(5.57 min vs 4.65 min,t180=-46.61,P< 0.001)after their partner left nests.We provide the first evidence that,under natural environmental conditions,both males and females respond to reduced partner effort with diverse strategies(match,partial compensation,or full compensation).In this long-lived species with long-lasting pair bonds and low fecundity,a mate mainly compensate for reduced partner investment to avoid forfeiting the current breeding attempt.This complementary pattern made the allocation of incubation task more flexible for two cranes and thus incubation patterns exhibited characteristics of ?short bouts,frequent changeovers and high efficiency?,helping reduce the conflicts between embryos and parents,and between two parents,and contributing to the adaption to alpine plateau environment.The crane's behavior reflects its many survival strategies.Nest attendance,recess frequency,on-bout duration and egg turning frequency were calculated for each time periods during the day(6:30-20:29)to investigate how crane parents adopt to the changeable alpine environment.Parents spent more time on the nest,took less recess,prolonged on-bout duration as ambient temperature was lowest between 06:30 and 08:29 h.At higher temperature between 10:30 and 12:29,the relationship reversed.The two parents responded differently to changing temperatures.Females spent more time on the nest at lower temperatures(06:30-08:29;58.88% vs 36.60%)and males increased their time on the nest with females' nest time reducing(12:30-14:29;47.69% vs 40.64%).The lowest egg turning frequency was between 18:30 and 20:29 h(female: 1.70 turns/2-h;male: 1.37 turns/2-h)and the highest egg turning frequency was between 12:30 and 14:29 h(female: 2.29 turns/2-h;male: 2.20 turns/2-h).The risk of embryo injury from chilling reduced when nest attendance increased as ambient temperature declined,and the parents' need for feeding satisfied when nest attendance declined with increases in ambient temperature.The incubation rhythm demonstrated that crane parents incubated in different but complementary way,and efficiently enhanced egg care in a dynamic environment.Using satellite telemetry,we monitored the migration of two Black-necked Cranes in China to study their activities before migration and determine migration routes to wintering areas.Satellite-tracking data indicated cranes were present in their territory most of the time,and home ranges prior to migration were respectively 0.55 km2 and 1.55 km2.Both cranes shifted roost site throughout the season.The maximum distances from the nest sites to roost site were respectively 3.22 km and 1.29 km.Cranes started to migrate on 8 and 14 November 2015,took off between 10:00 and 11:00.Only one crane was tracked successfully from YCW to its wintering area in Linzhou country,Tibet.The total entire migration route was 1101 km,lasted for 7 days(including 4 rest days at stopover site of Dachaidan lake).BNC in YCW migrated southwest,passing through the Tuergendaban Mountain and Chaidamu Mountain,resting at Dachaidan Lake and Yangtze River Basin in Qinghai Province,flying to Tibet via Tanggula Mountain Pass,and finally getting to the wintering area in Linzhou country.During breeding season,this crane was active at Baida,Hutoushan reservoir and its nearby areas.According to the migration routes,BNC in YCW belong to the west population.This study is the first to document the migration route of west population by satellite tracking,which is of great significance to habitat protection and population conservation of BNC. |
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