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).