Wintering Ecology Of The Long-eared Owls In Chongming Island

Long-eared owl (Asio otus) belongs to Strigidae Strigiformes, and it is medium-sized owl (35-40cm). It is also national second class protected bird. Long-eared owl is widely distributed in the world. Long-eared owl lived in China is migratory bird in most areas, which in Heilongjiang, Jilin and Liaoning province, east of Neimenggu province, northeast of Hebei province is summer resident, which from Hebei, Beijing to Xizang, Guangdong, and the provinces southeast coastal is winter resident. But in Xining of Qinghai, Kashgar and Tianshan mountain of Xinjiang, the bird is resident.Long-eared owl migrates between wintering and breeding ground, an important factor affecting its migration is the changes of the light length, in addition, food plays an important role to habitat selection of long-eared owls. But many phenomena show that the migration of long-eared owls is not exactly like those migratory birds in stable phenology.From2010to2012, we did ecological monitoring to wintering long-eared owls: long-eared owl went out for preying at dusk, and returned in the early morning. Long-eared owl flied out after sunset, and the time period was17:00pm～18:02pm; they returned before sunrise and the time period was05:25am-06:08am. The photometric quantity at outgoing and returning was4.8～0Lux,0～0.3Lux.Long-eared owls perched in the trees during the day, food could not be digested was ejected as pellets between08:00am and17:30pm. Most pellets were oval object, dark and their dry weight were between0.26g and6.00g, containing animal bones and hair, bird bones and feathers, grain, plant seeds, animal tail undigested and so on.According to Chongming Island Wildlife Resources survey results, Apodemus agrarius was the advantage specie of rodents in the farmland surrounding Dongping National Forest Park, and its high percentage showed that food resource was an important influence factor to habitat choice of long-eared owl. By monitoring, record some data about habitat of long-eared owls in Baodao Resort and Yiqinyuan Resort, such as vegetation type, height, cover degree, and the distance away from human. Analysis showed that vegetation type, height, cover degree can influence their choice of habitat. Long-eared owl preferred pine and cypress, cover about75%of the trees, but distance of human was not obvious requirement.Collected, dried, isolated and identified food pellets, the results showed that in wintering from2010to2011,98.31%of the food was animals for Rodentia Muridae,1.69%was birds of Passeriformes; and from2011to2012, rodent's percentage of animals fed by long-eared owls in winter was down to92.57%, percentage of birds was7.43%.Apodemus agrarius was the most important food of long-eared owl, so analysed age composition of it and found that youth group (0%), subadult group (13.29%), adult group Ⅰ (45.66%), adult group Ⅱ (27.17%), old group (13.87%). In winter of2011to2012, youth group (0.33%), subadult group (18.15%), adult group Ⅰ (37.29%), adult group Ⅱ (28.05%), old group (16.17%). Age composition of Apodemus agrarius preyed by long-eared owl was similar to that in wild, this meant that the predation of long-eared owl was random.From2011to2012, we analysed the pellets that one Long-eared owl had spitted out, and found that in November and March, the dry weight was the heaviest; from December to February, the dry weight is lighter. Though the samples were fewer, they can basically show the appetite change of Long-eared owl.