Study On The Diet Composition Of Saunders’ S Gull(larus Saundersi) Using Stable Isotope Technique

Saunders’ s gull(Larus saunderi) is listed as a vulnerable species by IUCN and Birdlife International. With continuous loss and degradation of natural wetlands, 85% world population of Saunders’ s Gulls breeds in anthropogenic wetlands. However, very few studies focused on the diets of Saunders’ s Gulls in different anthropogenic wetlands. To better understand the diets of this gull species, three breeding grounds were screened to conduct the study on their diet composition from May to July in 2014. One breeding ground is located in Shuangtaihekou National Nature Reserve(NNR), where is the largest breeding ground in the world and its breeding population was concentrated in one artificial wetland since 2008. The other two grounds are located in Yellow River Delta NNR, where is the second largest breeding ground and its breeding populations distribute in two restored wetlands. Feather and blood samples of adults and fledglings of Saunders’ s Gulls were collected to determine the diet composition using stable isotope analysis. Management recommendations were also proposed to sustaining the bright perspectives of this vulnerable gull species. Main results of this study are concluded as follows:1. The diet composition reflected from blood samples of fledglings was consistent with that from feather samples in Shuangtaihekou NNR. Main food sources(contribution ratio of blood and feather samples, respectively) include: Bullacta exarata(33.57%, 36.64%) Nereis succinea(31.41%, 31.20%), Synechogobius hasta(12.86%, 14.49%), Macrophthalmus dilatatum(9.19%, 8.08%), and Helice tientsinensis(7.48%, 6.00%).2. The diet composition reflected from blood samples of fledglings was consistent with that from feather samples in Yiqianer Management Station of Yellow River Delta NNR. Main food sources(contribution ratio of blood and feather samples, respectively) include: Bullacta exarata(22.97%, 20.72%), Nereis succinea(19.92%, 19.82%), Periophthalmus cantonensis(18.47%, 19.19%), Macrophthalmus dilatatum(10.83%, 10.53%), and Synechogobius hasta(8.82%, 9.51%). However, the dietary information of Saunders’ s Gulls between Yiqianer andDawenliu Management Stations showed distinguished difference. Main food sources and relevant contribution ratio in Dawenliu of Yellow River Delta NNR showed as follows: Macrophthalmus dilatatum( 31.44%), Nereis succinea( 17.05%),Periophthalmus cantonensis(16.71%), and helice tientsinensis(15.00%).3. The values of δ13C and δ15N of feather samples did not show any distinctive difference between disease, dead, and healthy fledglings. Furthermore, the values between the blood and feather samples of fledglings also show non-significant difference. These indicate nondestructive sampling such as feather samples from dead gulls can replace damage sampling, such as feather and blood samples from healthy individuals. Contrarily, the value of δ13C of feather samples between adult and fledglings has a remarkable difference. This means that the adult feather reflect the nutrition from long-term metabolism due to the incomplete molting. The feathers of fledglings were formed in the breeding ground, which reflect the nutrition accumulation in a short term.