Diet Niche Partitioning By Four Wintering Cranes In Poyang Lake

Crane(Gruiformes,Gruidae)is one of the most endangered groups of birds.Poyang Lake,the lagrest freshwater lake in China,is an important wintering area for cranes,supporting about 98% of the global population of Siberian crane(Leucogeranus leucogeranus;CR),most of the Chinese population of white-naped cranes(Grus vipio;VU),1/3 of the hooded cranes(G.monacha;VU)and 1/2 of the common cranes(G.grus;LC).In recent years,with the degradation of environment of Poyang Lake,The froaging areas and dietary of cranes have changed,and agricultural fields have become an important froaging aeras for cranes.Exploring the new dietary of cranes is the basis of effective protection and the premise of understanding coexist mechanism.In this study,we focused on the four wintering cranes in Poyang Lake: Siberian crane,white-naped crane,hooded crane and common crane.We used metabarcoding and fecal microscopy to analyze 129 fecal samples collected in winters of 2017/2018 and 2018/2019 to explore: 1)food composition and temporal change of diet of the four cranes;2)niche breadth and overlap between species;3)potential application of metabarcoding in diet studies;and 4)the role of agricultural fields in crane protection.The main results and conclusions of this study are as follows:1.In the winter of2017/2018,the four cranes were mainly foraged in agricultural fields.The food of Siberian cranes composed of 18 plant species belonging to 10 families,with rice(Oryza sativa,21.61%)and lotus roots(Nelumbo nucifera,54.84%),being their main food items.The food of white-naped cranes composed of 17 plant species belonging to 8 families,with Tulipa edulis(26.70%),Potentilla limprichtii(20.76%),Polygonum criopolitanum(11.74%),Carex(15.16%)and rice(11.58%)being their main foods.The food of hooded cranes composed of 19 plant species belonging to 11 families,with Potentilla limprichtii(54.01%)and Carex(23.82%)being their main foods.The food of common crane composed of 21 plant species belonging to 11 families,with rice(58.68%)and Potentilla limprichtii(12.03%)being their main food.In the winter of 2018/2019,most cranes return to natural wetland,only somecommon cranes and some hooded cranes still foraged in agricultural fields.The food of Siberian cranes composed of 17 plant species belonging to 11 families,with tubers of Vallisneria spp.(63.24%)and Polygonum criopolitanum(20.4%)being their main foods.The food of white-naped cranes composed of 18 plant species belonging to 12 families,with Polygonum criopolitanum(42.79%)and Potentilla limprichtii(12.43%)being their main foods.The food of hooded cranes composed of 12 plant species belonging to 9 families,with Polygonum criopolitanum(49.14%)and Vallisneria spp.(16.21%)being their main foods.The food of common cranes composed of 16 plant species belonging to 10 families,with Polygonum criopolitanum(41.88%)and rice(33.73%)being their main foods.2.The diet of Siberian cranes changed greatly between the two winters.In the winter of 2017/2018,rice and ltus roots were the main foods,while in the winter of2018/2019,Siberian cranes returned to natural wetlands and their main food changed to tubers of Vallisneria spp..The food compossition of white-naped cranes and hooded cranes mainly composrd of plants from meandow,with the main food items changed greatly in the two winters.In the winter of 2017/2018,rice occupied a certain proportion of white-naped cranes and hooded cranes,while it decrease to 0%in the winter of 2018/2019.The diet of common cranes had little change,with rice and Polygonum criopolitanum being the main foods in the two winters.Agricultural fields play an important role in crane protection.For Siberian cranes,agricultural fields are important refugia in food shortages.For white-naped cranes and hooded cranes,agricultural fields are places where they take supplementary foods.For common cranes,agricultural fields are important foraging areas.3.Siberian cranes and hooded cranes had a narrow dietary niche breath.It indicates that they have a strong selection on food sources.White-naped cranes and common crane had a wide dietary niche breath,which means they can utilize a wide range of food resources.The diet overlap indexs among the four cranes were between0.29 and 0.52,with the overlap index between white-naped cranes and hooded cranes(0.52)being the highest,and the index between Siberian cranes and hooded cranes being the lowest(0.29).The low overlap indexs indicate that the four cranes differentiated moderately in diet niche to achieve coexistence.4.By comparing the analysis results of metabarcoding and fecal microscopy,we found that the metabarcoding provided a higher resolution in unveiling food composition of cranes,which indicates that it has a great application potential in dietary studies.However,comparied to fecal microscopy,metabarcoding identified fewer main food items,and the proportion of each food was higher.This indicates that metabarcoding has a disadvantage in quantifing food abundance.Therefore,we recommend integrating several methods to comprehensively and accurately understanding the diet of birds.