| Play behavior is a kind of happy and enjoyable activity.Play behavior is reflected in the early ontogeny of many animals and is one of the important behaviors in animal postnatal development.Although many species exhibit play behavior,our understanding of this particular behavior is limited.The most widely accepted theory is that play is a mechanism for providing physical exercise,developing movement and training for emergencies.However,the function of play may vary from species to species,and within a given species may vary according to age,sex,dominant relationships,and environment.The study of play behavior often produces different results in different animal groups,so it is necessary to carry out the study of play behavior in a wide range of animal groups.Bats,an evolutionally-successful species,rely on echolocation sound waves to fly through the night sky and are found anywhere in the world except Antarctica.Most echolocation bats are late-maturing animals,and their young go through a critical growth period after birth.During this time,they develop appropriate sensory and motor skills,undergo wing morphology and echolocation growth and development,and are then able to live independently from their mother's care.Newborn bat cubs develop rapidly,so they have only a short time to develop flight skills.Flight skills are gradually acquired during the development of young bats.As a special skill,it can be a measure that more directly reflects the impact of play on bat development.Therefore,the study of play behavior in early bat development,especially play behavior that may be related to flight,can show the impact of play behavior on the development of young animals in a relatively short period of time.It is of great significance to reveal the adaptive function of play behavior in the development of young animals.In this study,infant bats were domesticated in the laboratory in a simulated natural environment.Identify individuals by a tag ring.Infrared camera and ultrasonic recorder were used to record the behavior and sound waves of bat in the process of bat development.According to the existing definition and criterion of animal play behavior,the play behavior types of young bats were classified.The body weight and forearm length of the young were measured at regular intervals.We investigated the effects of age and scaled mass index on the behavior development of young bats.At the same time,through the design of flight experiments,the flight ability of bats was tested,to explore the possible adaptive function of young bats in locomotor play.The following main experimental results were obtained.1)According to the definition of play behavior,there are four kinds of play behaviors in the developmental stage(3-25 days old)of Asian parti-coloured bat,which are crawling play(3%),moving head play(7%),flapping wings play(38%)and spreading wings play(52%).2)The locomotor play behavior of young bat has obvious temporal characteristics.The two kinds of play behaviors of crawling play and moving head play reached their peak around the age of 6 days,and then showed a decreasing trend.At the age of 17 days,the infants no longer showed crawling play and moving head play.Flapping wings play and spreading wings play increased and then decreased with the growth of the young bat's age,reached its peak at about 15 days old,and then began to decline.The young bats did not show any play behaviors after 25 days old.3)The results showed that the number of occurrences of crawling and moving head behaviors were influenced by scaled mass index(GLMM,Z = 5.62,P < 0.001),age(GLMM,Z=-3.62,P < 0.001),and the interaction between scaled mass index and age(GLMM,Z=-3.62,P < 0.001).When the age of the infants was controlled,there was a significant positive correlation between scaled mass index and crawling and moving head behaviors(R = 0.34,P < 0.001).When the scaled mass index was controlled,there was a significant negative correlation between the age of infants and crawling and moving head behaviors(R =-0.39,P < 0.001).The results showed that the number of occurrences of spreading wings and flapping wings behaviors were influenced by scaled mass index(GLMM,Z = 4.16,P < 0.001),age(GLMM,Z = 4.27,P < 0.001),and the interaction between scaled mass index and age(GLMM,Z = 4.27,P < 0.001).When the age of the infants was controlled,there was a significant positive correlation between scaled mass index and spreading wings and flapping wings behaviors(R = 0.47,P < 0.001).When the scaled mass index was controlled,there was a significant positive correlation between the age of infants and spreading wings and flapping wings behaviors(R = 0.19,P = 0.03).The results of the polynomial analysis showed that the number of occurrences of spreading wings and flapping wings behaviors increased and then decreased with age4)The sex of young bats was not the main factor affecting the frequency of crawling and probe behavior(LMMs,t = 0.07,P > 0.1).The sex of young bats was not the main factor affecting the frequency of spreading wings and flapping wings behaviors(LMMs,t =-0.31,P > 0.1).5)Young bats that exhibit more spreading wings and flapping wings behaviors try to fly earlier(Spearman's rank correlation,R =-0.46,P = 0.01).But young bats that exhibit more spreading wings and flapping wings behaviors do not necessarily gain the ability to fly freely faster(Spearman's rank correlation,R = 0.25,P = 0.46).In summary,this paper,based on the commonly used definitions and judgment criteria in current play behavior research,is the first time to identify and classify the locomotor play behavior of juvenile bats,elucidate its developmental changes with age and scaled mass index,and explore the relationship between play behavior and flight ability development. |
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