イヌワシの巣におけるヤマドリの就塒行動

抄録

Roosting behavior of the Copper Pheasant Syrmaticus soemmerringii was recorded by fixed video cameras situated at the nests of the Golden Eagles Aquila chrysaetos built on rock ledges in Iwate Prefecture, northern Japan. The first record of roosting was observed at about two hours before sunset on the evening of June 12, 2009. A female Copper Pheasant accompanied by 10 chicks (approx. 7–10 days after hatching) appeared on the eagle's nest which the eagles had not visited for about two months after they failed in breeding. After a few minutes wandering around the nest, the hen and the chicks gathered near the center of the nest and stayed overnight. They left the nest a few minutes after sunrise the next morning. The second record was obtained at another nest belonging to the same pair of eagles just prior to sunset on March 1, 2011. A female Copper Pheasant appeared on the nest which had been used by eagles up until 17 days prior. It stayed on the pile of twigs overnight and left the nest before sunrise the next morning. Golden Eagles that are major predators of Copper Pheasants, and staying on their nests may increase the risk to the pheasant of predation. However, roosting on cliff ledges seems to offer advantages to Copper Pheasants of a quick escape from mammal predators by flying down to the ravine, and shelter from rough weather.