INTRODUCTION
Due to the impact of human activities, nonnative plant invasions are
increasing worldwide (Stewart et al., 2021; Dawson et al., 2017; Seebens
et al., 2017). This causes local species biodiversity and habitat change
(Doherty et al., 2016; Blakeslee et al., 2011; Liba et al., 2009; Vilà
et al., 2011). The Smooth Cordgrass Spartina alternifera is a
perennial graminoid C4 plant with a well-developed root system that is
native to the Atlantic coast of North America (Wang, 2006). In the
1970s, it was introduced into the east coast of China because of its
good silting promotion and land building and wave elimination berm
function. It has been more than 40 years since then, and it has expanded
to more than ten provinces and cities along the coast of China (Yang,
2020; Deng et al., 2006). Smooth cordgrass was added to the first list
of 16 invasive alien species in 2003 and has required complete removal
from China’s coastal areas. Studies have shown that Smooth Cordgrass
invaded the coastal areas of China, occupying the bare beach and
shrinking the growth space of native vegetation, resulting in the
decline of original biodiversity due to changes in the habitat (Yu et
al., 2022; Zuo et al., 2012). With the increase in invasion time, it has
also been proven that some native passerine birds have begun to be
adapted invaded habitats, they enterd Smooth Cordgrass and rely on
exotic plants for foraging, avoiding, flocking, perching and
reproduction, this change may be related to the amount of time Smooth
Cordgrass has been invading native habitats (Chen et al., 2019; Chen et
al., 2022). The shrinkage of native habitats due to Smooth Cordgrass
invasion and human disturbances may drive more birds that rely on native
vegetation (Reed, Phragmites australis ) to attempt using the
invaded habitats, although invasive vegetation may be an ecological trap
(Ma et al., 2014; Chen et al., 2019). However, the existing studies and
reports of native birds entering Smooth Cordgrass are report
nonspecialised birds, which are widely distributed in different habitats
and have strong adaptability. Specific birds are highly dependent on
specific habitats due to their narrow niche and, therefore, are more
affected by exogenous disturbance (Dehling et al., 2021; Jorge et al.,
2014).
The Reed Parrotbill, Calamornis heudei , belonging to the
Passerine family, is a small, rare bird species inhabiting in obligate
reed wetlands. The Reed Parrotbill is an endemic species in China and is
distributed in the reed wetlands of the eastern coast of China and the
middle and lower reaches of the Yangtze River (Zheng, 2017; BirdLife
International., 2017). It is listed as a national level II key protected
animal in the newly adjusted ”List of National Key Protected Wild
Animals”. It is highly dependent on the reed habitat, all stages of life
history (including nesting, hatching, brooding, and overwintering) are
completed in reeds (Xiong et al., 2013). It exclusively uses the reed
community for foraging and reproduction and has a weak flying ability,
so it generally does not migrate. The bird only inhabits large reeds in
freshwater rivers, lakes, and coastal areas. During the breeding season,
it prefers to use a mixture of new, old, and dense reeds for nesting. In
the unharvested Reed habitat, the density of Reed Parrotbill is
significantly higher than that in the harvested Reed habitat. (Boulord
et al., 2011). The Reed Parrotbill is an obligate insectivorous bird.
During the breeding season, they mainly feed on Orthoptera and scale
insects on the surface of the reeds and in the stems. In winter, they
mainly feed on the overwintering eggs in dry reeds (Xiong et al., 2014;
Xiong et al., 2013). The Reed Parrotbill is a monogamous bird. It
usually starts to nest in May. Each nest generally has 5 eggs, with an
annual output of 1- 2 nests. The male and female parents take turns to
incubate eggs, and the brooding period is about 12 days (Hubert, 1914).
When they are in danger, they usually cluster escape, guardsman behavior
and warning call, therefore, it is very difficult to observe its
behavior (Wang, 2018). At present, there is no accurate assessment of
the global effective population of the Reed Parrotbill, but it is listed
as Near Threatened (NT) on the IUCN Red List due to the possible decline
of suitable habitat (native contiguous reeds) (BirdLife International.,
2017).