Figure 2
From: Determination of Original Infection Source of H7N9 Avian Influenza by Dynamical Model
(a) The cycle of bird migration. (b) The migration time of birds in Yangtze river delta area. From November to January, migrant birds stay in wintering grounds. The northward migration of birds to breeding areas can be observed from February to April. From May to July, migrant birds stay in north areas to reproduce the next generation. From August to November, since the temperature in the northern region begins to decrease, migrant birds have to migrate to wintering grounds again. For Anseriformes related to H7N9 spread, Yangtze river delta area is the wintering ground. The time of emigration is from the 5th week to the 17th week and the time of immigration is from the 36th week to the 48th week.
