Habitat loss and shift of the population centroid will make
migration
process more
difficult.
The
habitat loss also deteriorates the connectivity between adaptation areas
(Finch et al., 2017). The migratory birds have less food on the flyways
and have to fly longer distance to achieve the migration. These
conditions do not only make the migration process harder, but also
retains many birds from completing the process. Migratory species
require appropriate survival conditions throughout their whole migration
process, including the breeding process, the wintering process and the
migration between the
2
process (Rushing et al., 2016). Climate change may affect the 3 process
all and lead species to spend more energy and time to migrate.
With
the increasing of distance and the unstable of food, the difficulty of
survival for migratory species will increase (Finch et al., 2017;
Rushing et al., 2016; Saino et al., 2011). Especially for the
long-distance migration, the risk of death will increase a lot (Bauer &
Hoye, 2014; Kirby et al., 2008; Yong et al., 2018).
The importance of environment variables
The percentage contribution of
different variables can be seen by the
jackknife test in the MaxEnt model.
The determination of the leading factor for the migratory birds is
derived from the comparison of the contribution rate of
the
environmental variables involved in the model.
The
result of estimating the importance of variables showed
that\(t_{\min}\) was the most crucial environmental variable for
distribution of migratory birds, accounting for 23.02% importance.
The
LUCC, alt, bio1 and NDVI also
made
massive contributions to the model, accounting for
15.2%,18.64%,12.97%
and 12.22% importance respectively. The sum of the 5 essential
variables accounted for 82.05% of the cumulative contribution rate. The
individual contribution of these variables can be seen in Fig 3a.