Understanding the foraging behavior is essential for investigating seabird ecology and conservation, as well as monitoring the well-being of the marine environment. Breeding seabirds adopt diverse foraging strategies to maximize energy gains and cope with the intensified challenges of parenting and self-maintenance. Such trade-off may stem from the heterogeneity of food resources and the constraints of central place foraging. Nevertheless, abundant marine productivity could alleviate the energy limitation for seabirds, resulting in a consistent foraging approach. Here, we investigated the foraging strategy during the breeding season of a cryptic small-sized seabird, Swinhoe’s Storm-petrel (Hydrobates monorhis), in the Yellow Sea, a productive marginal sea of the Northwest Pacific. Using GPS tracking, we evaluated habitat preference, quantified the foraging strategy, and tested if environmental conditions and individual traits influence foraging trips. We found that Swinhoe’s Storm-petrels preferred nearshore areas with shallow water and engaged in primarily short foraging trips. Distinctive southeastward and southwestward strategies emerged when combining trip metrics, including foraging direction, duration, and maximum distance. The bathymetry, proximity to the coastline, and sea surface temperature differed in two foraging strategies. Foraging strategies exhibited flexibility between individuals, potentially explained by wing morphology, in which longer-winged birds are more likely to embark on longer-distance foraging trips. These findings highlight the impact of environmental factors and individual traits on seabirds’ foraging decisions in productive marginal sea ecosystems. Our study also provides valuable insights into the foraging ecology of this Asian endemic storm-petrel.

Reproduction investment is a prominent trade-off in life-history theory and is subject to strong selection pressure. The avian eggshell, as a crucial barrier between the bird embryo and the surrounding environment, undergoes optimization under different environmental selection regimes to ensure the successful development of embryos, which can be linked to local adaptation. Therefore, understanding the variation in eggshell microstructure and composition in wild bird populations living in contrasting ambient environments is of great significance. In this study, we utilized electron microscope ultrastructure measurement and elemental analyses to measure and compare the microstructure and element composition of eggshells from three wild plover populations (Charadrius alexandrinus and C. dealbatus) residing in heterogeneous habitats across varied climatic zones. These populations include the high-altitude Qinghai Lake population, the temperate coastal Tangshan population, and the tropical coastal Zhanjiang population. Our findings revealed that the palisade layer was thinner in the Qinghai Lake population compared to its lowland populations. This difference might be attributed to hypoxia which facilitates the hatching process by allowing chicks to easily break through their shells. Additionally, the variations in the elemental composition of the eggshells among populations well reflected the distribution of element content in different geographical regions. The Qinghai Lake population displayed low zinc and low manganese levels but high calcium levels, while the Zhanjiang population exhibited high zinc, high iron, high manganese, and high phosphorus levels. Furthermore, these variations in elemental composition could also account for the observed microstructural differences among populations. Collectively, we propose that the dissimilarities in eggshell microstructure and elemental composition among populations could be attributed to adaptations to different environmental conditions. Our findings lay the groundwork for future research to explore the mechanisms behind the variations in eggshell characteristics among wild bird populations, and contribute to a broader understanding of biodiversity mechanisms.

The Beijing Swift (Apus apus pekinensis) is a typical cavity-nesting bird that often nests inside holes and crevices in old architectures. Direct observation of their breeding behaviour is challenging and their breeding ecology is thus poorly studied. In this study, we analysed light-level geolocation data collected from six Beijing Swifts for the first time. Our results showed that geolocators can make comprehensive inference of their incubation period and behaviour. As a cost-effective and non-invasive method, geolocators can not only facilitate discovering migration routes, but also can be widely applied in the study of avian reproductive behaviour, especially in cavity-nesting bird species. We further discussed the characteristics and merits of this method and compared with other conventional nest-monitoring methods in recording birds.