Breeding Ecology Based On Video Surveillance And The Role Of Snake Slough In Nests Of The Crested Myna

Ornithologists have mostly studied the breeding ecology of birds in the northern temperate regions,with relatively few studies focusing on birds in tropical areas.Research into tropical birds can provide a unique opportunity to test ecological and evolutionary theories.In this study,the breeding ecology of the crested myna(Acridotheres cristatellus)in the tropical Hainan island,China,was investigated by integrating video surveillance with field observations,during the breeding season from March to August in 2018 and 2019.In addition,the role of snake slough as non-structural materials was investigated.The main results and conclusions are as follows:1.Breeding season of the crested myna occurred from mid-March to mid-August,and there were two breeding peaks.Both male and female parents build nests,and nests are slightly disk-shaped with an outer layer mainly composed of coarse plant materials such as twigs,grass roots,and stems,and an inner layer composed of feathers,snake slough,green leaves,plastic.Eggs were oval and pure blue-green in color.Egg mass,egg size,and egg volume were 6.78±0.50 g,28.74±1.20 mm×21.13±0.53 mm,and 6.56±0.50 cm~3,respectively.The nesting period in 2018(6.79±3.31 d,n=24)was significantly shorter than that in 2019(9.76±4.53 d,n=25,P=0.008).2.Both male and female parents took turns incubating their eggs and co-brood nestlings during the day,with a brooding period of 18–22 d.The clutch size between 2018(3.90±0.41,n=58)and 2019(4.00±0.61,n=28)was no significant difference(P=0.75).The incubation period in 2018(12.67±1.06 d,n=21)was significantly longer than that in 2019(11.95±0.89 d,n=20,P=0.048).There was no significant difference between the time period of nestling brooding and feeding in 2018(19.85±1.35 d,n=20)and 2019(20.44±1.21 d,n=16,P=0.223).Egg hatching success,breeding success and fecundity showed no significant difference(P>0.05).3.The egg laying of crested mynas was mainly observed between 7:00 to 10:00 a.m.,and the average time for laying one egg was 172.36±28.29 s(n=11).During the incubation period,parents left their nests more than 70 times per day at different incubation stages,and the daily incubation rate was about 70%,with longer incubation time occurring 7:00 and 9:00a.m.of the day.The daily feeding low ebb for parents appeared 14:00–16:00 p.m.,with feeding times in the mid-brooding stage being significantly higher than those in the early stage(P=0.005).4.The length of snake slough added by crested myna to the nest is 2-18.3 cm.The addition of snake slough continued throughout the entire breeding period,and the proportion of the added snake slough was up to 38.9%during the nest-building period.The utilization rate of snake slough in 2018(38.5%)was significantly lower than that in 2019(71.4%,P=0.005).No significant differences were found in clutch size,egg mass,egg size,the number of nestlings hatched for each nest and breeding success between nests with snake slough and nests without snake slough(P>0.05).However,nestling mass comparisons between the two groups showed significant differences,with nestlings in snake slough growing faster than nestlings in non-snake slough group(P=0.019),and the nestling period of the snake slough group was significantly shorter than that of the non-snake slough group(P=0.041).5.The predation rate of the experimental group with snake slough(41.7%)was significantly lower than that of the control group(100%)(P=0.005).In the anti-predatory experiment,the egg predation rate of the experimental group(41.7%)was significantly lower than the control group(100%;P=0.005),and the proportion of the first predation of eggs were significantly lower in the experimental group(8.3%)than in the control group(83.3%;P=0.001).In the olfaction experiment,there was no significant difference in the predation rate and the proportion of the first predation of eggs by the squirrels between the two groups(P>0.05).In the vision experiment,the proportion of the first predation of eggs of the experimental group(8.3%)was significantly lower than in the control group(66.7%;P=0.009).In the slough length experiment,the length of the slough did not have a significant effect on the predation rate of the nest box(P>0.05).In conclusion,in contrast with crested mynas found in the temperate zone,parent birds in tropical areas showed earlier nesting time,earlier first egg laying date,and longer breeding periods.These results suggest a breeding strategy specifically adopted by tropical birds such as the crested myna in Hainan island.Second,nestlings mass in snake slough growing faster than in non-snake slough group,and the nestling period of the snake slough group was significantly shorter than that of the non-snake slough group.These results suggest snake slough in crested myna nests may serve to improve the immunity of nestlings or serve as a post-mating sexual signal eliciting differential reproductive investment in mates.In addition,this study showed that the snake slough added in the nest has the function of anti-predation,and the visual factors of snake slough affect the nest predator.However,the length of the snake slough did not have a significant effect on the predation rate.These results indicate that the snake sloughs in bird nests can effectively deter nest predators,mainly via their visual effect.Our study provided further experimental evidence for the hypothesis that snake slough in birds'nests acts as a nest predator deterrent,suggesting that mynas and other tropical species with higher nest predation pressure may have evolved the behavior of using snake slough as a non-nest material to reduce the risk of nest predation.