关键词: 稳定同位素, 年际变化, 迁徙鸫, 食性生态位分化, 迁徙停歇地

Abstract

Aims: Closely related species with similar ecological traits often achieve coexistence at migratory stopover sites through niche differentiation; however, their dynamic coexistence mechanisms and resource allocation patterns under interannual environmental fluctuations are not yet fully understood. Furthermore, existing avian dietary studies often rely on single fecal micro–histological analysis, which may lead to the underestimation of the nutritional contribution of soft–bodied food items.Therefore, it is important to conduct multi–dimensional cross–validation by incorporating stable isotope techniques. 

Methods: To address these gaps, we investigated three migratory thrush species—Eyebrowed Thrush (Turdus obscurus), Grey-backed Thrush (Turdus hortulorum), and Japanese Thrush (Turdus cardis)—at an autumn stopover site in Mingxi, Fujian Province. Combining fecal micro-histological analysis, plasma stable isotope(δ¹³C and δ¹⁵N) analysis, and local food source sampling, we quantified and compared their dietary composition and isotopic niche dynamics across three consecutive years (2021–2023). 

Results: (1) Fecal analysis revealed that berries such as Aralia chinensis were frequently consumed in 2021 and 2023 (frequency > 60%), whereas the detection rate of invertebrates (Termitidae, Formicidae) increased in 2022. However, stable isotope analysis demonstrated that invertebrates, particularly spiders (Araneae), were the primary source of assimilated nutrition for all three species (median contribution > 70%), indicating that relying solely on fecal inspection may underestimate the nutritional importance of soft-bodied soil invertebrates. (2) During the anomalous autumn drought in 2022, the three thrush species exhibited distinct dietary differentiation and species–specific niche response strategies. The larger-bodied Grey-backed Thrush expanded its isotopic niche width, displaying an opportunistic foraging strategy. The intermediate–sized Eyebrowed Thrush similarly broadened its isotopic niche width, demonstrating high dietary plasticity; its reliance on berries decreased from 66.1% in 2021 to 57.9% in 2022, while increasing its consumption of invertebrates. In contrast, the smaller-bodied Japanese Thrush adopted an opposite strategy by contracting its niche width and maintaining highly specialized exploitation of spiders (contribution rate >72%) to cope with drought stress. (3) Although overlaps existed in their overall isotopic niches, the overlap probabilities of their core isotopic niches consistently remained low (below 40%), demonstrating clear fine-scale partitioning of core resources. 

Conclusions: Our findings suggest that these three migratory thrushes may cope with environmental fluctuations through highly plastic dietary adjustments and fine–scale partitioning of core resources. This study provides a new perspective for understanding the stable coexistence mechanisms of multi–species communities at stopover sites, and simultaneously offers essential scientific support for the habitat management and conservation strategies of migratory bird communities within the East Asian–Australasian Flyway (EAAF).

Key words: stable isotope, interannual variation, migratory thrushes, dietary niche differentiation, migratory stopover sites