Abstract
I studied the characteristics of roosting habitat for Eastern Marsh Harriers Circus spilonotus and Hen Harriers C. cyaneus in Okayama Prefecture from October 2011 to September 2015. Harriers were observed to roost in three types of reed bed habitats, include sites with reed and sedge, sites with reed only, and parts of the reed bed where the reed was lodged by wind. Reeds are said to be “lodged” after wind has blown them from a vertical to a partially horizontal position. The majority of Eastern Marsh Harriers and Hen Harriers roosted in habitat with only reeds. Eastern Marsh Harriers, however, changed roost habitat seasonally. In July to October, use of reed-and-sedge habitat decreased, and use of the reed bed sites where the reed was lodged by wind increased. It is assumed that the seasonal changes of roost habitat was influenced by temperature, risk of predation, and density of plants.
