Individual study: Rice paddies left unploughed appear to provide better foraging areas than autumn-ploughed paddies for wintering red-crowned cranes Grus japonensis and white-naped cranes Grus vipio, Cheolwon area, CCZ, South Korea
Lee S.D., Jabłoński P.G. & Higuchi H. (2007) Winter foraging of threatened cranes in the Demilitarized Zone of Korea: behavioral evidence for the conservation importance of unplowed rice fields. Biological Conservation, 138, 286-289
The Demilitarized Zone (DMZ) and the Civilian Control Zone (CCZ) between North and South Korea contain some of the most important wintering sites (due to limited development) for the endangered red-crowned crane Grus japonensis and the vulnerable white-naped crane Grus vipio. Farmers in the CCZ plough now most paddy fields after the autumn harvest rather than in the spring as they traditionally did; how this might affect crane foraging activity was assessed.
Study area: The study was undertaken from 21 December 2002 to 25 January 2003 in the Cheolwon area (38.07-38.45ºN, 127.04-127.57ºE), CCZ, South Korea, adjacent to the DMZ with North Korea. Between 250-300 red-crowned and 200-350 white-naped cranes winter in this area each year.
Foraging observations: Observations (mostly between 09:00-12:00 h) were made in both winter-fallow and autumn-ploughed rice paddies. Foraging cranes (14 red-crowned, 38 white-naped) were videoed from a vehicle at a distance 200-300 m. Activity of each individual was categorized at 15-s intervals as either feeding (i.e. neck bent towards the ground and head/bill focused on the soil surface in search of food) or not feeding. Food intake was not measured, as the video image did not allow differentiation between successful and unsuccessful pecks.
Red-crowned crane feeding activity was based on an average observation period of 4.2 min/individual (n = 3) for ploughed and 9.9 min/individual (n = 11) for unploughed fields; and for white-naped crane an average 4.4 min (n = 7) for ploughed and 6.3 min (n = 31) for unploughed fields.
Overall, cranes observed on the unploughed paddies spent more time foraging than on adjacent ploughed paddies. By species, of the three red-crowned cranes observed in the ploughed fields, none foraged at all; in the unploughed field, four of the 11 cranes observed foraged for on average 27% of observation time. White-naped cranes in ploughed fields either did not forage or foraged for only a short period (average 3% of observation time); in the unploughed fields, all of the cranes actively foraged (average 48% of observation time).
Conclusions: The authors suggest that the foraging behaviour observed is an indication that the unploughed fields contain more food resources for the cranes than do the ploughed fields. It is acknowledged the sample sizes are small, part due to limited access in the military zone, combined with the cranes’ sensitivity; often they flew off upon approach of the vehicle. However, it is hoped that further observations will be made.
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