Strategies For Nest-Site Selection In Double Brooding Great Tit (Parus Major)

Double brooding(breeding two nests in the same season)is one of the common strategies for many birds to maximize their reproductive efficiency,but not all individuals in a given population undergo double brooding,and the ratio varies from year to year.The double brooding of birds is affected by many factors,such as food availability,length of breeding season,nest site microenvironment,parental input,and breeding experience.Due to the short life span of small birds and the difficulty of tracking and monitoring them,few studies researched about the strategies of the selection of nest sites for double brooding.From March to August 2018-2019,I took the great tits(Parus major)in the Zuojia Nature Reserve in Jilin Province,adopted the methods of banding mark,specimen experiment and alarm sound playback were used,combined with the date accumulated by the research group from2014 to 2017,discusses the nest site selection strategies in double brooding great tits from three aspects:nest site feature selection,predation pressure impact and social information utilization.We found a significant difference in the direction of nest entrance between used(n=115)and unused(n=109)nests of great tits during their second broods process(GLMMs,?~2=4.212,P=0.04).However,not all the used and unused nest,when including nests of the first broods and second broods,showed significant difference in nest height,nest entrance orientation and nest inclination angle.For the tracked of double-brooding individuals,we found significant difference between their first and second nests in the nest entrance orientation but not in nest height and nest inclination(Paired Samples T test,Z=-2.359,P=0.018,n=38).The used nests have a more downward nest inclination,which may act as rainwater-proof.The nest entrance of their second nests for the double-brooding individuals are mostly towards southeast and southwest,rare in the northwest,suggesting that they prefer to select a leeward,sunny nest to keep nest warm and to avoid the prevailing northwest wind.The double-brooding individuals showed anti-predation in their nest site selection(LMM,t=2.101,P=0.036).Under natural circumstances(n=26),the nest distance between their first and the second nests was about 57.6 m.The distance significantly increased to 82.4 m when predation pressure increased(n=17).This indicated the predation pressure may affect the nest sites selection of double-brooding great tits.Great tits preferred to choose a place around large number of neighbors with a higher number of nestlings and higher breeding success rate for nesting as second broods nest site,and tend to be close to conspecific nests,and appropriately away from heterospecific nests.The results suggest that tits may use potential social information to make second broods site selection decisions,such as the presence,reproductive density and reproductive performance of conspecific and/or heterospecific individuals.