Research On The Seasonal Variation In The Diet Composition And Selection On The Tidal Crabs Of The Red-crowned Crane(Grus Japonensis) In Yellow River Delta

The research on the food and habitat use of red-crowned cranes in one of the most important migratory stopover, Yellow river detla, is very helpful to understand the migration strategy and energy reserve for this endangered species. Furthermore, it is useful for the population conservation and habitat management for this species.Red-crowned crane (Grus japonensis) is a rare and endangered bird of China, listed as Grade 1 national level of China in the Endangered Species Red Book, and also listed as Critically Endangered species by IUCN Red list. It is estimated that the global population is about 2910-3100 individuals. Red-crowned crane distributed in Russia, China, Korea, South Korea and Japan. All the population of the red-crowned cranes are migratory, except 1000 individuals in Japan. Red-crowned cranes breed in Zhalong Nature Reserve, Heilongjiang Province and Xianghai Nature Reserve, Jilin Province in China, and winter in Yancheng Nature Reserve. The Yellow River Delta and Liaohe Delta are the two most important migratory stopover for red-crowned cranes in China. And the whose migration distance for the Chinese migratory crane population is about 1500 km.Red-crowned cranes largely depends on the high-quality food resources in the stopover to refuel for migration. In recent years, the food resource of red-crowned cranes have been threatened in the Yellow and Bohai Sea due to loss of the coastal wetland. Red-crowned cranes use different food resources and habitats in different migration season. In this study, we used behavioral observation and fecal analysis to explore the migration trends, habitat use, food composition and foraging strategy of the red-crowned cranes in the Yellow River Delta Nature Reserve. The seasonal variation in the food use is also discussed.Red-crowned cranes arrived in Yellow River Delta focusing on February 14 to March 15 in spring and November 15 to December 5 in autumn. The spring migration is more concentrated. The main habitat used by Red-crowned crane is Suaeda mudflats and Spartina mudflats. No seasonal difference in the habitat use have been found..The main food of red-crowned crane in Yellow River Delta was tidal mudflat crab, fish, snail and shell. The tidal mudflat crab was the predominant food of red-crowned cranes (Frequency:99.6%; Percentage of the composition:94.2%). There was no significant seasonal variation between spring and autumn migration. The two main crabs in the prey of red-crowned cranes are Helice tridens tientsinensis and Macrophthalmus dilatatum.Red-crowned cranes preferred to eat the H. tientsinensis crabs (80.1%) than M. dilatatus crabs (19.9%). The percentage of H. Tientsinensis in the fecal of red-crowned craneswas significantly higher in spring (88.5%) than that in autumn (60.5%).The sex and size of crabs that red-crowned cranes ate were significantly different from the crabs in natural habitats. Red-crowned cranes showed a significant preference for female H. tientsinensis crabs (78%) in their diet. The sex ratio of female H. tientsinensis crabs in the fecal was significantly higher in autumn (81.4%) than spring (76.7%). However, Red-crowned cranes showed a significant preference for male M. dilatatus crabs (99%) in both migration seasons, and there was no significant seasonal variation. Red-crowned cranes showed a significant preference for smaller H. tientsinensis crabs to feed [diet vs habitat, shell width (mm): 21.59±0.12 vs 24.89±0.51]. However, Red-crowned cranes showed a significant preference for larger M. dilatatus crabs [diet vs habitat, shell width (mm):28.90±0.34 vs 22.30±0.25]. There was no significantly varation in the AFDM both between species and sex.