Fig.10. The comparison of nature reserves and suitable areas in China

Comparing the current distribution of birds and the protected area, we can find out that the suitable areas and nature reserves do not match very well. One of mismatch is that the large number of migratory birds lives in the middle and lower reaches of the Yangtze River Plain but protected area is only located around the Dongting Lake and Poyang Lake. The other of mismatch is the position of habitat and the protected area, there are lots of habitats are not protected. The distribution of protected areas in different regions of China is very uneven, with large areas of protected areas in western China, but the distribution of birds is mainly concentrated in the eastern of China (Ma et al., 2019). Migratory birds tend to choose plain areas that are easily to fly to and feed successfully, so that they can save energy and have a high probability of survival. The western human population is rare, thus, it is easily to manage the reserves and prevent them from artificial effect. However, the situation in the east is more complex because of its position as the agriculture center and its dense population. The protected areas in the eastern area are scattered and broken, and the connectivity between them is also broken(Sang et al., 2011).

Our results indicate some new views about the impact of climate change on bird populations. Firstly, an effective regulatory frame should be built based on the establishment of protected areas. The area of nature reserves in China increases a lot since 2000, but the protective effect is not effective. There are 2 main reasons for this. The first reason is that the location of nature reserves mismatches the distribution of migratory birds (Ma et al., 2019). China is still in the process of high speed development focusing on the economic activities and the urban expansion, which will reduce the space for birds(Liang et al., 2018b; Liang et al., 2017). The second reason is the lack of rational management for nature reserves. The nature reserves locate in the sparsely populated regions in China, which leads to few workers in the large area (Shen et al., 2015). Effective conservation measures must be established for the protection of species, not only to establish effective nature reserves, but also to take effective policies to reduce the impact of climate change on species distribution.

Secondly, different regions should be combined for protection. We can see the similarity of the constraints in different regions. The fact in China is that the nature reserves are isolated from other places. The borders of different provinces, climate zones and the basins are the blind spots for species protection. The mismatching borders among province, basins and climate zones makes it more difficult to manage the cross zones between these areas. Specifically, there are different protection policies to select nature reserves, since China is a wide country with different regulations and standards (Liang et al., 2018a). Which guidelines should the border areas follow and what kind of managements should these areas take are not clear.

Thirdly, the protection of whole birds and individual birds should be distinguished. According to our research, the influence of climate change on species distribution will rise in future. Many species of migratory birds will decrease in distribution and population in future climate scenarios, and may even face the risk of extinction(Pereira et al., 2010; Pimm et al., 2014). Also, some of the species will retain or expand in future. The distribution of each species is different from other species and changes every year. Considering the suitable conditions for the individual species, we can choose a region for this species and control the environmental conditions to meet demand.

Finally, the effective policies should be taken to combat climate change. Climate change has a critical influence on the distribution of birds, therefore, it is necessary to keep the climate relatively stable by making policies. Temperature is the constraint of birds in whole China. The carbon emission making temperature rising has a great influence on the distribution of birds, so it is necessary to reduce the carbon emission (Beringer et al., 2011). Also, the constraint in southern China is NDVI, which suggests that we should keep forest coverage floating within a certain range. At last, biodiversity loss is heavily international problem, all the countries on earth should unite together to protect biodiversity.

This work was supported by the National Natural Science Foundation of China (51679082, 51979101, 51479072, 51521006), the Hunan Science & Technology Innovation Program (2018RS3037), the Natural Science Foundation of Hunan Province (2019JJ20002) and the Three Gorges Follow-up Research Project (2017HXXY-05).

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