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Heilongjiang Research Institute of Wildlife, Hapin Road, Harbin City, Peoples Republic of China

Lidan wetland, in the lower reaches of the Wuyuer River, is an important bird rest area and one of the main breeding areas for cranes (Gruidae). Waterflow, level, distribution, and quality in the wetland have a direct effect on the breeding of cranes.

This study addresses the relationships between water, vegetation, aquatic animals in the wetland, and six species of cranes. Nests of Red-crowned cranes (Grus japonesis), white-naped cranes (G. vipio) and common cranes (G. grus) lie in the reed marsh where the water depth is about 20-40 cm, and the water depth around the nest is about 40-60 cm. The water appears to protect the nests from animal and human approach. The adult cranes add reeds to protect their eggs and chicks when the water level rises.

Demoisell crane (Anthropoides virgo) builds its nest on the ground in sparse woods or dry grassland far from water. Siberian white cranes (Grus leucogeranus) and hooded cranes (G. monacha) migrate through the wetland every spring, usually staying for more than one month. Siberian white cranes forage diurnally for corn and the roots of the aquatic plants in the reed marsh in about 10 to 20 cm of water. They loaf and rest in shallow water, but the water depth around such sites is about 50 cm, so other animals and humans cannot approach. Hooded cranes glean wheat grain and herb seeds in wheat fields, and rest in the wet grass where the water level is about 10 cm.

Red-crowned cranes, white-naped cranes, demoiselle cranes, and common cranes forage not only in the marsh, but also in cropland. The animal food they obtain there includes fish, shrimp, and insects. Plant foods include tender shoots and leaves of reed as well as seeds of other plants.

The water level influences breeding and feeding of cranes. When water levels are high, breeding success is low. Food may be inaccessible. When water levels are low, the quantity of food in water is reduced, and probability of predation of the nest and eggs is increased.