The Song And Its Territorial Defense Strategy Of The Dusky Warbler In Breeding Season

Territoriality exists in a variety of animals.Territory is the place where animals occupy resources,reproduce and rest.The territorial defense behavior of birds protects all kinds of resources in the field and provides guarantee for the successful reproduction of birds.Over the long term,birds have taken a series of measures to defend themselves against invaders,but their response to intruders may vary depending on the singing behavior,physical condition,physiological hormones and social factors of individuals in the field.The dusky warbler(Phylloscopus fuscatus)in Saihanba,Hebei province,was selected as the research object,during its breeding period from 2018 to 2019,song playback and other methods were used to simulate field invaders,and strong directional microphone and recorder were used to record the spontaneous song and the induced song during invasion of individuals in the field.At the same time,the spatial defense behaviors of individuals in the field were observed.After the playback,target individuals were captured by the mist nets,morphological parameter were measured and blood samples were collected.The blood corticosteroid levels of individuals in the field were detected by the enzyme linked immunosorbent assay(ELISA).To explore whether the dusky warbler can adjust its defense behavior according to its own state and relative threat of the invader.The results showed that:(1)the number of song verses and the song rate of the male territorial owners were significantly increased responding to the intruder's song;(2)individuals with lighter weight and shorter tarsometatarsus sing more verses(r =-0.310,p = 0.048)with higher maximum frequency(r =-0.464,p = 0.005).The shorter the latent time to start singing(r = 0.348,p = 0.030),the earlier they approached the range of 3m(r = 0.339,p = 0.033),and the longer the retention time(r =-0.354,p = 0.027);(3)the plasma corticosterone levels in individuals with lighter weight and shorter tarsometatarsus were higher than that of the individuals with heavier weight and longer tarsometatarsus(r = 0.372,p = 0.021).Our study demonstrated that the territorial defense response of male dusky warblers was affected by its physical conditions.The smaller the body size,the stronger the territorial defense response,and the higher the level of corticosteronesecreted into the plasma.The social identity of the territorial invader is also an important factor affecting the individual defense strength.The study of the dusky warbler showed that male individual reactions to different identity intruders are obviously different,compared with the neighbors,when the stranger invasion,individuals in the field of song defense and space defense are stronger,showed a strong "dear enemy effect" phenomenon.However,differences in physical quality between individuals did not affect responses to strangers and neighbors.This suggests that the male dusky warbler can recognize the social identity of intruders through song,and that individuals in the field pay more attention to social identity than physical quality.At the same time,the defense level and attack intensity can be adjusted according to the perceived threat level.There was no significant difference in the frequency of S-song pattern and V-song pattern(P>0.05),except for the lowest frequency(P < 0.05),other parameters showed no significant difference(P>0.05).This shows from the side that the song of the dusky warbler is relatively stable without interference.But due to the competition for mates,defending the territory,maintaining food resources,their own health status and other factors,song will be adjusted within a certain limit,so as to adapt to the stress of reproductive life,improve their own fitness.This study combining song,behavior,physiology,and social identity,etc.,to the dusky warbler territorial defense strategy has carried on the comprehensive research,found that for the dusky warbler,different types of individuals have different defense strategies.Domain owners can judge by song and make reasonable and effective defense against intruders.This study improves the effective territorial defense strategies adopted by birds during breeding period,and also supports and complements the familiarity theory of "dear enemy effect".