Animal gut is a dynamic ecosystem, and there are many factors affecting the structure of intestinal flora and the diversity of intestinal microbes, among which food differences are the direct causes. To investigate the effect of food composition on the intestinal flora structure of mandarin duck during the reproductive period, 9 feces were collected from 2 foraging sites of Shiqian Mandarin Duck Lake National Wetland Park, Guizhou, China. We analyzed the chloroplast rbcL gene, mitochondrial COI gene and 16S rRNA gene from the total DNA of the feces in detail to know the plants and animals in food compositions and intestinal bacteria of mandarin duck by high-throughput sequencing technology. We found that the gut microbiota composition were significantly correlated with the number of feeding species, the mandarin duck with a wide variety of feeding food had the more complex gut flora with more probiotics and less pathogenic bacterium. This study provides further theoretical support for food difference to affect the changes of intestinal bacterial structure of host, and provides scientific basis for understanding the feeding preference of mandarin duck at breeding area.

Background: Understanding how overwintering birds choose foraging habitats is very important for conservation management. The overwintering Black-necked Crane (Grus nigricollis) feeds on crop remains in farmlands; thus, reasonable conservation management of this type of farmland that surrounds wetlands is critical for the overwintering populations of the Black-necked Crane; however, it is not clear how the Black-necked Crane chooses the foraging land in the farmland. Methods: A thorough field positioning survey of all foraging sites in farmland areas around the Caohai Wetland and a sampling analysis of habitat selection by the Black-necked Crane were conducted during the winters from 2016-2017 and 2017-2018. Results: Multiple factors contributed to the selection of foraging habitat in farmlands, i.e., food factors (crop remains and tillage methods) > human disturbance factors (distance to road and settlement) > topography factors (slope aspect), listed according to the strength of influence. Additionally, Black-necked Cranes tend to choose farmland sites where there was no machine tillage, the crop remains were > 500 g/m 2 , the distance to residences ranged from 100 to 500 m, the distance to roads ranged from 50 to 100 m, and the slopes exhibited western or eastern aspects. As the winters progressed, the volume of the edible crop remains declined, and the influences of the other main factors also changed, i.e., the factors of human disturbance (distance to road and settlement) became less important, while the effect of the food factor (crop remains) was strengthened. Thus, the foraging sites near the road became more important. Conclusion: The farming area surrounding the Caohai Wetland is very important for the overwintering Black-necked Crane. Food factors and human disturbance factors are the main factors that influence the choice of feeding ground.

The silver spoon hypothesis proposes that individuals which develop under favorable conditions will gain fitness benefits throughout their lifetime. Hatching order may create a considerable size hierarchy within a brood and lead to earlier-hatched nestlings having a competitive advantage over their siblings, which has been illustrated in some studies. However, there have been few explorations into the effect on subsequent generations. Here, using a 15-year-long study, we investigated the long-term fitness consequences of hatching order in the endangered crested ibis, Nipponia nippon, a species with complete hatching asynchrony. In this study, we found strong support for silver spoon effects acting on hatching order. Compared with later-hatched nestlings, first-hatched nestlings begin reproduction at an earlier age, have higher adult survival rates, possess a longer breeding life span, and achieve higher lifetime reproductive success. Interestingly, we found carry-over effects of hatching order into the next generation. Nestlings which hatched earlier and became breeders in turn also produced nestlings with larger tarsus and better body condition. Additionally, we found a positive correlation among life-history traits in crested ibis. Individuals which started reproduction at a younger age were shown to possess a longer breeding life span, and the annual brood size increased with an individual's breeding life span. This suggests that the earlierhatched nestlings are of better quality and the "silver spoon" effects of hatching order cover all life-history stages and next generation effects.

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