Abstract
Hunting flights by Eastern Marsh Harriers Circus spilonotus were studied to investigate the effect of ponds created for restoration in Watarase Marsh, Tochigi Prefecture, Japan. The frequency of hunting flights, hunting behaviors and time spent (minutes) on hunting flights were recorded from mid-October to November of 2004 and 2014, and from January to February of 2015. The study area was classified into two habitat types, including a restoration site with newly created ponds, and a dry reedbed consisting of common reeds Phragmites australis and Japanese silver reeds Miscanthus sacchariflorus. In November of 2004, before the creation of ponds, the frequency of hunting flights by harriers were significantly more frequent in dry reedbed than at the restoration site. From mid-October to November of 2014, after the ponds were created, the frequency of hunting flights and hunting behaviors by harriers were significantly more frequent in the restoration site than in dry reedbed. In the autumn season, the newly created ponds had numerous waterfowl such as ducks, grebes, and Coots Fulica atra, which are major prey species of the harrier in the study site. The duration of hunting flights was also significantly longer over the restoration site than at the dry reedbed. From January to February 2015, however, there was no significant difference between the two study sites in the frequencies of hunting flights and hunting behavior, nor of the time spent during hunting flights. At the restoration site during that time, the availability of waterfowl as prey appeared to be poor. In order to create ponds as hunting habitat for the harriers throughout the wintering season, therefore, it is necessary to construct wetlands with ponds that have more suitable structure for wintering waterfowl. This can be accomplished by managing water depth and vegetation structure.
