The Ning-Shan Crested Ibis (Nipponia Nippon) Is Re-introduced Into The Population's Overnight Cluster, Individual Survival Rate, Population Growth Rate And The Alli Effect

The Crested Ibis(Nipponia nippon),once was in the brink of extinction,has been listed as the national first-grade protected animal and endangered species in China Species Red List.A series of great protection efforts for nearly four decades had brought the number of Crested Ibis population back to a sustainable level.The protective goals we have achieved are summarized as follows.Since the rediscovery in Yangxian County in 1981,the wild population has increased from 7 individuals to more than 1,550,with another approximately 1,600 captive-bred birds which resided in 16 conservation centers and zoos in China,Japan and Korea,respectively.Enough captive-bred individuals make it possible to reintroduce the species to the wild.In the present study,the protection of the difficulties we are facing is how to overcome the obstacles,Allee effect on small population growth,as well as the impact on introducing the success rate.Allee effects,the reduction of individual fitness at low population densities,can occur through several mechanisms,all of which potentially apply to reintroduced populations.According to the Re-introduction Specialist Group of the IUCN,a reintroduction is any attempt to establish a species in an area that was once part of its historical range,but from which it has been extirpated or become extinct.Since the number of organisms released in reintroductions is usually much lower than the site-specific carrying capacity,and the reintroduced populations are initially at low densities,hence Allee effects can potentially lead to reintroduction failure.Therefore,we would focus on the reintroduced population of the Crested Ibis in Ningshan County by investigating demographic parameters such as annual variation of population number,productivity,adult or juvenile survival and average annual population growth rate.We aim to determine the relationship between the fitness parameter and average annual population growth rate to ibis population size which could demonstrate the causing mechanisms,types and strengths of Allee effects in the ibis population.As reintroductions are almost invariably characterized by small propagule sizes,the importance of the Allee effect must be considered in order to assess its potential impact on the probability of success in reintroductions,and we must consider this potential impediment to the survival,increase,and spread of small groups of reintroduced individuals in order to propose strategies for minimizing Allee effects and build more wild populations with genetic vigour.It is helpful to rescue the endangered species of crested ibis from the root source.Banding,radio-telemetry and field motoring were used to research Allee effects relevant to mate limitation in our focused population.The study birds include 56 released individuals and their offspring produced in the wild from 2007 to 2017.The main results are summarized as below:(i)A total of 40 breeding pairs were formed from 2008 to 2017.Of 267 eggs produced from 81 clutches,193 nestlings were hatched successfully in 10 breeding seasons.The annual average hatching rate was 72.28%± 0.383(n=10).In total,135 nestlings successfully fledged and annual average fledging success rate was 69.95%±0.125(n=10),annual average fecundity per pair was 1.69 ± 0.17(n= 10),and the breeding success was 50.56%.Although a self-sustaining population has formed,we found that the population grew slowly with negative growth rate in some specific years.The population size has been in a low level in recent years.(ii)On whole population level,females are more unbalanced than males.The sex ratio structure was transferred from female-biased to male-biased pattern.The age structure is pyramidal,indicating a continuously growing population.(iii)The size of night-roosting flock is not related to the area and elevation of habitat area,but may be related to the distribution of food resources and habitat quality.Also,the crested ibis prefer tall trees for the night-roosting site,such as Chinese pine(Pinus tabulaeformis)and Chinese red pine(Pinus massoniana).(iv)The night-roosting flock was formed early in the autumn and winter season,mainly in the family group and the small flock of 5 ?9 individuals;In the medium term,individuals of 13 to 21 are common,and there is an increasing number of subadults in the group,and the formation of the breeding pair occurs in this period.The cluster disintegrates at the end,and the proportion of individuals in different age group is close.(v)The annual suevival rate for adults,juveniles and yearlings with best model Sa3,Pa3,r.,F.averaged at 0.812±0.03,0.678±0.066 and 0.544±0.066,respectively,which was similar to that of the wild population.(vi)The relationship between the pairing rate and the sex ratio is the bell type function.The more skewed the sex ratio,the lower the pairing rate.The number of matched pairs was positively correlated with the size of the cluster in autumn and winter.That is,the larger the cluster size,the more the annual number of new pairs.(vii)We simulated the age-structured Leslie-matrix model for 25years using the estimates of survival rate and fidelity.There was a 3-fold increase in population size at the end of 25-year simulation,and the average population growth rate was larger than 1(mean=1.075,with 95%CI:1.069-1.087),showing a positive population trend during the 25-year simulation period.(viii)Based on the previous studies about female-biased natal dispersal and breeding disperal,we continue to discuss the causes of the Allee effect,including dispersal,sexual selection,habitat fragmentation,predators and climate change.We also analysis the factors resulting in mating difficulties in males caused by sex ratio imbalance,lower individual fitness,especially the lowest percentage of the juveniles,means the lower number of potential mate,indicating the mate limitation in the population.The mate-based Allee effects resulting from mate limitation,that is,component Allee effects not only can lead to the mate-finding difficulty,lower mating rate and lower productivity,but also can accumulate to become demographic Allee effect.If the weak demographic Allee effect converts to strong Allee effect,the population size will decrease.The extinction may occur when the population size was lowest.(ix)The management suggestions and minimum strategies of Allee effect were also proposed.