Wednesday, 3 February 2016

Hooded Cranes

Chongming Dongtan is one of the most important wintering sites in China for Hooded Cranes, with the majority of the population wintering in Japan at one site, Izumi.  It is a threatened and declining species with a global population of around 11,000 birds.  At Chongming Dongtan, it winters primarily on the saltmarsh.  Sea Bulrush Scirpus mariqueter is a dominant species in the saltmarsh vegetation; and its corms and seeds form a major food source for the cranes (and other wintering waterbirds such as Tundra Swan).  One study showed that the corms and rhizomes composed about 99% of the total food content of the cranes.  

The corms in the outer saltmarsh zone (far from the seawall) are easier to find by the cranes as they are buried underground shallower than those in the inner zone due to daily erosion by tidewater. So, for easy access to food, Hooded Crane tended to select the regions near the channels at low tide as their foraging habitat.  Despite the similar food content between Hooded Crane and Tundra Swan, obvious ecological separation occurs in their foraging behaviour, foraging times and foraging habitats.  

However, the native Scirpus mariqueter dominated tidal vegetation is highly threatened and diminishing rapidly.   Land reclamation is a major threat all along the Chinese coast but the native vegetation is also being out-competed by the non-native Smooth Cord-grass Spartina alterniflora  (the eradication of which is the focus of our project at Chongming).  Human activities such as fishing, and notably eel fishing at Chongming Dongtan, have resulted in serious disturbance to the Hooded Crane and other waterbirds.  Although the cranes continue to focus their activity on the remaining good quality saltmarsh, they now also increasingly feed in rice paddies just over the sea wall, particularly at high tide.  One of the reserve projects at Chongming is to create ‘sacrificial’ rice paddies in safe locations for the benefit of the cranes and other waterbirds.

We found a mixed flock of 70 Hooded and 18 Common Cranes loafing and displaying on the upper areas of the saltmarsh.  Interestingly, there was one family of apparent hybrid Hooded x Common Cranes, a not infrequent occurrence.  These birds displayed the bulk and general colour of the Commons but had a washed-out Hooded head pattern.

Pics- above: Hooded Cranes (with Common Crane in the background).
Below: cranes on the salt marsh with distant fishing boats and bouys, displaying Hooded and Common Cranes with some hybrids in the foreground.

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