[Objectives] Poyang Lake is the largest freshwater lake in China and one of the important wintering grounds for Tundra Swans Cygnus columbianus and Siberian Cranes Leucogeranus leucogeranus. They primarily feed on the tubers of the Vallisneria spp. in Poyang Lake, and reduce interspecific competition through spatial niche differentiation. In recent years, the quality of Poyang Lake wetland ecosystem has been deteriorating due to human activities and frequent flooding. The tubers of Vallisneria have been seriously degraded. A sharp decline of tubers of Vallisneria has led a large number of Tundra Swans and Siberian Cranes to shift their foraging habitats from natural wetlands to lotus ponds of the Nanchang Wuxing Siberian Cranes Reserve. Given the limited food resources in Lotus Ponds, the large numbers of Tundra Swans and Siberian Cranes at small lotus ponds may lead to an increase of interspecific competition, which may have a negative impact on the survival of one or both species. [Methods] In this study, we used the scan-sampling technique and focus animal method to investigate the diurnal behaviors, single feeding time, and foraging success frequency per minute of Tundra Swans in monospecific flocks and mixed-species flocks (i.e., flocks include Tundra Swans and Siberian Cranes) at lotus ponds of the Nanchang Wuxing Siberian Cranes Reserve. The investigations were conducted from November 10 to November 25, 2021. One-way ANOVA test or Mann-Whitney U test was used to analyze the data. [Results] The results indicated that foraging (45.59%), moving (17.05%), and resting (15.92%) were the main behaviors of Tundra Swans (Fig. 1). The peak foraging time of Tundra Swans was from 9:00 to 10:00 in the morning and from 16:00 to 17:00 in the evening, and the trough occurred from 11:00 to 12:00 in the noon (Fig. 2). These behavioral strategies may help Tundra Swans cope with the energy consumption at night. Tundra Swans in mixed-species flocks spent significantly higher proportion of time on foraging (47.62%) than that in monospecific flocks (43.34%) (Fig. 3). The average duration of feeding bouts of Tundra Swans in mixed-species flocks (10.90 ± 4.92 s) was significantly higher than that in monospecific flocks (9.96 ± 6.56 s) (Fig. 4). Interspecific competition might result in decreased food availability and lower foraging efficiency for Tundra Swans, hence Tundra Swans increased foraging time to compensate for the negative effects of interspecific competition and to satisfy the energy requirement. The foraging success frequency of Tundra Swans was significantly higher in mixed-species flocks (0.69 ± 0.55 times/min) than that in the monospecific flocks (0.52 ± 0.56 times/min) (Fig. 4). Tundra Swans can hardly get chunks of lotus root by swinging their flippers or pecking with flat beaks. After Siberian Cranes arrived at the lotus ponds, they pecked the lotus root to pieces with their long beaks, which might facilitate Tundra Swan foraging and hence improving their foraging success. [Conclusion] The results of this study indicate that the degradation of submerged vegetation in Poyang Lake has changed the foraging habitats and foraging space of Tundra Swans and Siberian Cranes. A large number of Tundra Swans and Siberian Cranes are competing for food at the same lotus ponds, and interspecific competition intensifying, which may have a negative impact on their survival. Tundra Swans coped with the negative impacts of interspecific competition by increasing foraging time. Our study contributes to the assessment of the potential impacts of submerged vegetation degradation on endangered birds such as Tundra Swans and provides a scientific basis for the formulation of bird conservation policies.