Effect of water level fluctuations on temporal-spatial patterns of foraging activities by the wintering Hooded Crane (Grus monacha)

Background The Yangtze River floodplain provides important wintering habitats for Hooded Cranes (Grus monacha) in China. Fluctuations in the water level change foraging habitat and food availability, affecting their temporal-spatial patterns of foraging activities. It is of considerable importance to investigate the effect of these fluctuations on food availability for wintering Hooded Cranes and their foraging response to these changes. Understanding their behavior patterns is beneficial in protecting the wintering crane population and restoring their wintering habitats.

Methods A field survey of the winter behavior of cranes was carried out at Shengjin Lake from November in 2013 to April in 2014. Habitat variables, as well as the spatial distribution and behavior patterns of wintering cranes at their foraging sites during five stages of water level fluctuation were collected. Based on this data we analyzed the relationship of foraging behavior relative to water level fluctuations and habitat types.

Results The foraging habitats used by Hooded Cranes varied at the different water level stages. As the water level decreased, the use of meadows and mudflats increased. When the water dropped to its lowest level, the use by the Hooded Crane in the mudflats reached a peak. There were statistically significant differences in time budget in the three types of habitats over the five stages of the water level. In the mudflats, the foraging behavior and maintenance behavior varied significantly with the water level, while the alert behavior showed little variation. Analysis of a generalized linear model showed that the five water level stages and three habitat types had a significant effect on foraging behavior, while the combined effect of these two variables was significant on the foraging time budget and the length of foraging activity of the Hooded Crane.

Conclusions With the decrease in the water level, the use of mudflats by Hooded Cranes increased correspondingly. Food availability in different habitats was affected by changes in the water level. The Hooded Crane adjusted its foraging patterns and made full use of the three available types of habitat in order to acquire enough food in response to fluctuations in the water level.