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The trophic relations of the red-crowned crane in Zhalong wetland, northeastern China may significantly be altered due to the rapid decrease in accessible food resources. To confirm this hypothesis, we determined the trophic status of this vulnerable species by using stable isotope (carbon (δ13C) and nitrogen (δ15N) methods. The δ13Cand 15Nsignatures in the red-crowned crane species were in the range of −17.8‰to −18.5‰and 6.9‰to 8.1‰, respectively. The majority of the ecosystem of Zhalong wetland has an average food-chain length of 3.9, and the trophic level of the examined species, i.e., red-crowned crane, was approximately 3.1. The trophic relations of red-crowned cranes have changed over the period of 2004 to 2014, as the biological species in the bottom trophic level significantly exhausted in the past years. The conflict of food demand by red-crowned cranes versus the livelihood demand of local wetland residents should be resolved to ensure sustainability of food supply sustainable for rare and extinguishable species.

The concentrations of six elements (Ca, Mg, Zn, Cu, Pb and Cd) in the eggshells of breeding red-crowned cranes (Grus japonensis) in China’s Zhalong Wetland were examined. Two macronutrients, namely, Ca and Mg, were predominant in the eggshells, with corresponding concentrations varying from 127 g kg−1 to 323 g kg−1 and 0.33 g kg−1 to 5.51 g kg−1 (dry weight, dw), respectively. The Cu and Zn contents were in the range of below the detection limit (ND) to 8.05 mg kg−1 and ND to 511 mg kg−1 dw, respectively. The maximal Pb and Cd concentrations in the eggshells of the red-crowned crane exceeded a level considered to be potentially toxic in birds (i.e., 1.7 mg kg−1 for Pb and 0.34-0.91 mg kg−1 dw for Cd), ranging from ND-3.20 mg kg−1 dw for Pb and ND-1.20 mg kg−1 dw for Cd. The principal components analysis results revealed the complex chemical associations between two essential (Cu and Zn) and nonessential (Pb and Cd) elements in the eggshells of G. japonensis in China. Increased Pb and Cd levels in the bodies and eggshells of the red-crowned cranes suggest this species in their colonies are exposed to these contaminants, although which had not induced to obvious eggshell thinning in the examined species.

The discovery of eight dead red-crowned cranes in Zhalong Wetland, northeastern China, allowed us to examine their digestive tracts for identifiable prey in this study. Stomach content and fecal analyses were used to determine the foraging ecology of this crane species. The stomach content mass of the red-crowned crane carcasses varied according to body size and ranged from 10.62 g to 26.32 g. Grit particles prevailed in the stomach of the birds and accounted for approximately 87% of the mass of the stomach contents by weight (mainly gravel with particle sizes of 2–10 cm). Gizzard contents included plant and aquatic animals, which made up 63% and 37%, respectively, of the weight. Maize, seed, and fish were the most common residues in the gastric content; and zoobenthic debris, seeds, and reed organs were markedly present in the crane feces. The combined use of stomach content and fecal analyses is recommended for future studies on the food habits of this rare bird species.