The Characteristics And Influencing Factors Of Dispersal In The Saxaul Sparrow (Passer Ammodendri)

The dispersal is a common behavior of birds,which significantly influences the success rate of individual reproduction,genetic structure and genetic diversity of the population,demography,geographical distribution,and species evolution.The research of dispersal behavior mainly aimed to reveal the factors affecting dispersal,including individual and environmental aspects.The Saxaul sparrow(Passer ammodendri)was researched in the present study.A method of follow-up survey was implemented in a breeding population of the saxaul sparrow in the Anxi Hyper-arid Desert National Nature Reserve,Gansu province.The foot-ring markers and breeding data from 2014 to 2019 were analyzed in this study.The size and reproductive performance of the philopatric and dispersal individuals in the breeding population were compared and analyzed to clarify the factors affecting the selection of natal dispersal and breeding dispersal of the saxaul sparrow,and exploring the influencing mechanism on the dispersal of the saxaul sparrows under extreme arid desert condition.A total of 3521 nestlings and 1312 adult birds were captured and marked.The breeding period data of 720 nests were collected,and the active area of 18 adult birds were recorded.By statistical analysis,the major results were as follows:(1)The saxaul sparrows was characterized by the female-biased dispersal pattern.The sex ratio of natal philopatric individual was 1.32:1(?:?).Specifically,for the first breeding more male individuals return back to their birthplaces,and natal dispersal partial of population was the female-biased dispersal.The breeding philopatric sex ratio was 1.14:1(male : female),and the sex ratio of whole population was 1.18:1(male : female)in the breeding periodThere was no significant difference in the number of male and female individuals which returned to the last breeding site for reproduction.It was indicated that the sex-biased dispersal was not obvious.(2)The data showed that the philopatric individuals take great proportion ofwhole breeding saxaul sparrows,with an average of 55.69±12.09% over six years.The average rate of returning adults who had bred at least once in this area was49.23±5.23%,which indicated that the site fidelity was strong during the adult reproduction.However,the average rate of natal philopatric rate was only6.46±1.10% in six years.Here,a low natal philopatric rate was related to the high mortality rate in the first year of newborn nestlings.Meanwhile,it was indicated that the natal dispersal rate of newborn nestlings was high and more newborn nestlings can be apt to spread out to find new breeding grounds.(3)After the breeding season,the activity range of saxaul sparrow was not limited to the nest site and surrounding areas,and the area of active areas and the core areas of male and female individuals was significantly larger than that of the breeding season.There was no significant difference in the active area and core area between males and females during the breeding season(n=18).According to the tracking results of one male and one female,the active area and core area of male was larger than that of female after breeding.These results suggested that females did not take greater range of motion or greater mobility than males.(4)By comparing philopatric individuals with foot rings with dispersal individuals in breeding population,some magnitudes measured in philopatric individuals were significantly higher than that of dispersal individuals,including the index of beak crack(t=3.875,df=707,P<0.01)and tail length(t=4.602,df=707,P=0.032)in the philopatric individual males,and the index of wing length(t=6.580,df=599,P=0.011)and tail length(t=12.868,df=599,P<0.01)in females.The main reason was that saxaul sparrows have a strong philopatry or site fidelity,then,after wandering and living in clusters in autumn and winter,at the beginning of breeding period,individuals with advantageous physical conditions and strong flight ability would go back to their original breeding sites or birthplace usually.(5)The influence from birth environments and parental status on the natal dispersal of nestlings were analyzed by the generalized linear mixing model(GLMM).It was indicated thatin the families with the first egg laid earlier(t=2.164,df=1,P=0.030),the fewer siblings disperse(t=2.668,df=1,P=0.008)and the second mother for fewer breeding numbers(t=2.502,df=1,P=0.012),more offspring were born to disperse.(6)The relevant factors of the dispersal in the saxaul sparrow were analyzed by the generalized linear model(GLM).It is illustrated that individuals(both male andfemale)with later date of the first brood of eggs chose to spread more during the second brood in the same breeding season.In the first litter,the lower fly-out rate of the offspring,the more females choose to dispersal.The fewer eggs there were in the previous year,the more females select dispersal in the following year.No other obvious factor was founded whether reproductive experience of first year could influence the breeding dispersal of second year or not.Options of individuals returning to their original home or dispersing to new breeding sites in breeding seasons can be related to a number of factors,including the experience of cluster roam in autumn and winter.