Species-Specific Accumulation and Temporal Variation of Metal(loid)s Shape the Population Trends of Large Wading Birds in the Eastern Province of Saudi Arabia

This study introduces a non-invasive method for monitoring environmental pollution by analysing metal(loid)s in the faeces of sentinel species. We measured the concentrations of four metal(loid)s, arsenic (As), chromium (Cr), cadmium (Cd), and lead (Pb), in the droppings of four large wading bird species (Little Egret, Great Egret, Reef Heron, and Striated Heron) from 2020 to 2024 in the wetland ecosystem of the Eastern Province of Saudi Arabia, a part of the Central Asian Flyway. Our results revealed significant level of the metal(loid)s in the bird droppings, indicating environmental pollution likely linked to industrial activities, agricultural runoff, and urban expansion. All metal(loid)s exhibited significant temporal variation, with increasing concentrations observed across species. Pb and Cd also showed rising trends but exhibited species-specific effects. While the metal(loid)s analysis confirms exposure and accumulation, it does not by itself allow definitive identification of pollutant sources. Based on previous environmental assessments and land-use data, the studied wetlands are known to be influenced by anthropogenic activities, suggesting that the metal(loid)s in bird faeces predominantly originate from local pollution. However, we acknowledge that further source-tracing analyses would strengthen this inference. This study highlights the need for continuous monitoring of metal(loid)s pollution to safeguard wildlife health and maintain ecological stability. Given the study area’s proximity to industrial zones, these findings advocate for enhanced pollution control measures and targeted management strategies to mitigate risks and conserve wetland habitats.