Parent-Offspring Conflict And Sibling Competition In Grey-Backed Shrike(Lanius Tephronotus)

Parent-offspring conflict is the maximization of parental fitness by allocating resources to offspring reasonably while offspring strive to obtain the most resources from their parents.The core theory of parent-offspring conflict in birds was proposed by Trivers in 1974,which detailed the dominance and changes in parent-offspring conflict.Sibling rivalry,on the other hand,is a behavior of siblings competing with each other to expand their own fitness,and the resource competition between nestling siblings is mainly regulated by their parents.This study explores the breeding strategies adopted by adult grey-backed shrikes(Lanius tephronotus)during the incubation and nestling-rearing stages in the highaltitude and cold environment of the northeastern margin of the Qinghai-Tibet Plateau during the five breeding seasons from 2017 to 2021,and analyzes the factors that influence the adoption of these strategies.At the same time,the study examines the factors influencing sibling competition among grey-backed shrike nestlings.The following conclusions were drawn from this study:(1)Grey-backed shrike parents have flexible incubation strategies,with 215 shrike eggs tested during the five breeding seasons from 2017 to 2021.This study shows that under the climate conditions of the Qinghai-Tibet Plateau,grey-backed shrike parents will adopt a large-clutch strategy with more giant eggs as the environment improves,thereby increasing their fitness.(2)In terms of nestling gender,the total gender ratio of nestlings in the five breeding seasons from 2017 to 2021 was slightly skewed towards males,but the sex ratio in 2021 differed from other years and tended to be female.GLMM analysis was conducted on the relationship between climate factors and nestling gender,nest sex ratio,and interannual sex ratio.The results showed a significant negative correlation between nestling gender,nest sex ratio,and interannual sex ratio with average temperature(P < 0.05)and a highly significant positive correlation between rainfall and nestling gender,nest sex ratio,and interannual sex ratio(P < 0.01).The one-way ANOVA indicated significant differences in the interannual sex ratio between 2021 and2019-2020,suggesting that climate can have an impact on nestling gender.(3)There was no significant difference in fledging weight and gape width between marginal and core offspring,but there was a significant difference in fledging wing length(P < 0.05).Marginal nestlings had the highest growth rates in body weight,wing length,and gape width,indicating that they prioritize the development of traits related to competitive ability,such as wing length and gape width,with available energy.Greybacked shrike nestlings follow the parenting strategy of asynchronous hatching to form core and marginal offspring: There were differences in body weight among nestlings,with core offspring being heavier than marginal offspring.In nests with smaller brood sizes,where sibling competition was less intense,the parents allocated resources more evenly,resulting in the more comprehensive development of nestlings.(4)The overall feeding rate of parent birds is influenced by factors such as brood size,nestling age,begging intensity,average rainfall,and wind speed.When the brood size is larger,and the nestlings are older,parent birds invest more in feeding.The feeding rate of parent birds is positively correlated with average rainfall(P < 0.05)and negatively correlated with wind speed(P < 0.05).Analysis of the feeding behavior of male and female parent birds showed significant differences in the effects of nestling age and average rainfall on the feeding rates of males and females.Male birds mainly undertake the feeding task,and their feeding rate increases with the age of the nestlings,while the feeding rate of female birds is unrelated to the age of the nestlings.The feeding rate of male birds is significantly positively correlated with average rainfall(P< 0.05),with more rainfall indicating better environmental conditions and abundant food supply.(5)The overall feeding preference of the parents is influenced by factors such as the age of the nestlings,whether they are core or marginal offspring,and the sex of the nestlings.As the nestlings’ age increases,the parents’ feeding input increases.During breeding,the parents prioritize feeding the marginal offspring to ensure nest survival.Both female and male parents tend to favor male offspring when feeding.Regarding food allocation,female parents dominate in providing food,while male parents dominate in delivering it.The feeding preference of both female and male parents is influenced by factors such as the brood sex ratio,whether the nestlings are core or marginal offspring,the age of the nestlings,and the sex of the nestlings.When the brood sex ratio skew towards male or female,the feeding preference of the parents aligns with the actual brood sex ratio.In nests with a male bias,as the age of the nestlings increases,the parents increase their investment in the nest,and raising male nestlings is more costly than raising female nestlings.The feeding preference of female and male parents is influenced by factors such as the average temperature and the sex of the nestlings.Male parents exhibit a strong preference for feeding male nestlings,whether in nests with a male bias or female bias,while female parents do not show a preference for the sex of the nestlings.As the average temperature increases,male parents prioritize caring for the core offspring and reduce their investment in the marginal offspring.(6)The nestlings display both true and false signals during begging,with false signals stronger than true ones.Nestling begging intensity is significantly influenced by factors such as parental feeding rate,whether or not they received food in the last feeding,the identity of the feeding parent,and the number of competing nestlings.Marginal offspring exhibit higher begging intensity than core offspring,indicating significant sibling competition.Nestling begging intensity(P < 0.05)negatively correlated with Parental feeding rate.In the context of parent-offspring conflict,parents have dominant control over resource allocation and adjustment,which can help reduce excessive sibling competition among nestlings.