| The Greater Crested Tern(Thalasseus bergii)is a seabird recorded breeding in East China Sea,but its breeding biology has not been researched.In recent years,it has been found breeding with the critically endangered Chinese Crested Terns(Thalasseus bernsteini)which drew much attentions.Since 2013,the tern restoration project were conducted at Jiushan Island in Xiangshan,Ningbo,which provide good chance to close study the breeding biology of the Greater Crested Tern.During the breeding season of 2018(from April to August),we conducted our researches at Tiedun Dao.Our aims include:breeding habitat selection,nest site selection,breeding timeline,breeding behavior,foraging ecology,breeding success and its influencing factors.The nesting ground was divided into 3X3 square meter grids,and the observation were from the blind beside the nesting ground.The additional observation tools include photography,video camera,infrared camera,and banding.The results include:1.In 2017 breeding season,about 2,500 Great crested terns and 26 Chinese Crested Terns were attracted to this island.The Great Crested Tern entered the island on April 25,laid first egg on May 17,the fledgling left first on August 10;Incubation period was 27 ± 3 days,fledging period was 30 ±3 days.2.The Great Crested Terns usually selected their breeding habitat at a small island off the coast.Their nesting grounds included grass,rock and a zone of interlaced rock and grass devoid of tall vegetation.The clutch size is one.3.Arrival Behavior:The Great Crested Terns usually circled over the breeding islands and calling.With individual increasing,the Great Crested Tern began to laying eggs;Courtship Behavior:Male tern usually holds a fish in its beak,going to find its mate.If the female tern feels right,would accept the fish.And then the couple would spread their wings around each other,dancing and eventually copulating.Incubation behavior:Egg was incubated by male and female birds in turns.While a bird incubating,the other would go to forage at the sea;Behavior of protecting nest:intimidating with nodding,elongating neck,shaking head,pecking with beak,even fighting away from the nest.After chicks hatched about 20 days,chicks usually leave their nests gradually and move to the reefs at water edge,and then learn to fly.4.Based on the data from the satellite tracking,the maximum radius of their foraging range is 109.67 km,the radius of 75%coverage range is 44.13 km,and the radius of 50%coverage range is 28.59 km.Great Crested Terns prey on various fishes which include 10 different fish species and some uncertainties.Carangidae,Harpadontidae and Trichiuridae account for 61%of their total food.Most of the fish fed to the young chicks(1-7 days)were small fish with the length of 0-25 mm.The elder chicks(over 7 days old)usually fed with 25?50 mm in length.5.Success rate of Great Crested Tern breeding in 2017 was 60.04%.Affecting factors include vegetation ratio,proportion of land,the decoy number within nest area,and the distance from sound source.There was a significant negative correlation between the proportion of vegetation and the breeding success rate.There was a significant positive correlation between the proportion of land,the distance of sound source,the decoy number and the breeding success rate.These results showed that the high proportion of vegetation will reduce the breeding success,and the higher nest area land ratio,more decoys and away from the sound source can increase the breeding success.6.12 Great Crested Terns banded in 2015 were observed,this indicated that the Great Crested Tern has the fidelity to natal habitat.7.There are similarity between the reproductive ecology of the Great Crested Tern and the Chinese Crested Tern:(1)They have close correlations in food variety and feeding frequency.(2)They have almost same clutch size(3)They have similar breeding time line.(4)They breed together,indicating that they are similar in breeding habitat selection and nest site selection. |
PDF Full Text Request