About 40 percent of people worldwide depend on rice, and ricefields have replaced natural wetlands in many areas. Conservation biologists frequently suggest that ricefields are suitable wetland habitat for wintering and migrating waterbirds. However, new research shows that waterbirds overwhelmingly prefer natural marshes to ricefields in the Camargue delta on the Mediterranean coast of southern France.
“Natural marshes had a greater abundance, species richness, and number of exclusive species,” say Christophe Tourenq of Station Biologique de la Tour du Valat in Arles, France, and his co-authors in the August issue of Biological Conservation.
Tourenq and his colleagues compared the abundance and diversity of waterbirds in ricefields and natural marshes of the Camargue, a 560-square mile delta where the Rhone River flows into the Mediterranean Sea. Ricefields comprise about a fifth of the Camargue’s wetland area. The researchers tallied the number and species of waterbirds in marshes and ricefields once or twice a week for a year. Altogether, they surveyed 69 marshes and 85 ricefields. Because ricefields are seasonally flooded with fresh water, the researchers primarily considered seasonally flooded, freshwater marshes.
Tourenq and his colleagues found that waterbirds were far more abundant in the marshes than in the ricefields: about 99 percent of the nearly 300,000 birds tallied were in the marshes. In addition, waterbirds were far more diverse in the marshes than in the ricefields: 28 of the 59 species observed were found only in the marshes, including vulnerable species such as the jack snipe (Lymnocryptes minimus), Kentish plover (Charadrius alexandrinus), and white stork (Ciconia ciconia).
The researchers also found that some waterbirds used ricefields more intensively than marshes, according to the season. For instance, sandpipers and gulls were common during the spring, purple herons (Ardea purpurea) were common during the autumn, and cattle egrets (Bubulcus ibis) were common during the winter. “Cattle egrets are a recent invader of the Camargue,” says Tourenq. “Current studies suggest that rice farming enhanced the settlement of this species in the Camargue.”
Tourenq and his colleagues caution that their findings may not apply to all ricefields. Camargue ricefields are typically flooded from spring to autumn and are dry during the winter, which presumably makes them less suitable for wintering waterbirds. In contrast, in many areas ricefields are flooded during the winter to attract waterfowl for game hunting. Moreover, even if marshes are better waterbird habitat than ricefields, in many areas ricefields are the only wetland habitat available for waterbirds.
For more Information
Tourenq, C. 2001. Are ricefields a good alternative to natural marshes for waterbird communities in the Camargue, southern France? Biological Conservation 100:335-343.