How bird type and diet impact waterbird populations

Jenn Hoskins
1st March, 2026

How bird type and diet impact waterbird populations

Anas acuta, one of the waterbird species examined in the study.

Photo adapted from: Oscar Alejandro Morales Juárez / CC BY SA (Source)

Key Findings

  • Waterbirds wintering along the Caspian Sea coast of Iran accumulate trace metals, with levels varying by species
  • Piscivorous birds (fish-eaters) showed the highest concentrations of lead, cadmium, chromium, and arsenic due to biomagnification in the food chain
  • Some birds had metal levels exceeding thresholds linked to potential health problems like kidney issues and impaired survival
Waterbirds are sensitive indicators of environmental health, accumulating contaminants from their food and surrounding habitats. Heavy metal pollution poses a significant threat to these ecosystems, impacting waterbird populations and potentially human health through biomagnification. Understanding the levels and patterns of metal accumulation in waterbirds is crucial for effective conservation and risk assessment. A recent study conducted by researchers at University of Mazandaran and King Fahd University of Petroleum & Minerals[1] investigated trace metal concentrations in waterbirds wintering along the southern Caspian Sea coast of Iran. The research focused on ten different waterbird species – Anas acuta (Northern Pintail), Anas platyrhynchos (Mallard), Anser anser (Greylag Goose), Aythya ferina (Common Pochard), Ciconia ciconia (White Stork), Cygnus olor (Mute Swan), Hydroprogne caspia (Caspian Tern), Mareca penelope (Eurasian Wigeon), Mergus merganser (Common Merganser), Phalacrocorax carbo (Great Cormorant), and Tringa totanus (Redshank) – collected during February 2013. The study analyzed eight metals in the secondary flight feathers of these birds: arsenic (As), cadmium (Cd), chromium (Cr), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn). Flight feathers were chosen as they provide a historical record of metal exposure, reflecting concentrations accumulated over time. The results revealed considerable variation in metal burdens across species. Great Cormorants (Phalacrocorax carbo) consistently exhibited the highest concentrations of all metals measured, with particularly high levels of lead (5.65 µg/g dry weight), cadmium (3.29 µg/g dw), chromium (5.90 µg/g dw), nickel (6.57 µg/g dw), arsenic (0.60 µg/g dw), manganese (9.30 µg/g dw), zinc (147.67 µg/g dw), and iron (267.29 µg/g dw). Conversely, Eurasian Wigeon (Mareca penelope) showed the lowest arsenic levels (0.13 µg/g dw), while Mute Swans (Cygnus olor) had the lowest cadmium (0.78 µg/g dw), chromium (2.32 µg/g dw), and nickel (1.22 µg/g dw). Interestingly, metal levels correlated with feeding habits. Piscivores – birds that primarily eat fish – displayed the highest concentrations of lead, cadmium, chromium, nickel, arsenic, and zinc. This finding aligns with the known bioaccumulation of these metals in aquatic food webs. Invertebrate predators, on the other hand, showed lower cadmium, arsenic, zinc, and iron levels. This suggests that the source of metal contamination is largely linked to the aquatic environment and the consumption of contaminated prey. These findings build upon earlier research highlighting heavy metal contamination in wetland ecosystems[2]. The Dongting Lake Wetland (DTW) study demonstrated that migratory birds are exposed to heavy metals through various pathways, including drinking water and food sources. While the DTW study found relatively low exposure through drinking water, it identified areas with concerning levels of cadmium and arsenic in the sediment, potentially impacting birds feeding in those locations. The study reinforces this concern, showing elevated metal levels in piscivorous birds, indicating that the food chain is a significant route of exposure. Furthermore, the ability of earthworms to immobilize metals in soils[3] presents a potential avenue for mitigating contamination. While not directly addressed in, the findings suggest that improving soil health and reducing metal bioavailability in key foraging areas could reduce exposure risk to waterbirds. The study also noted that cadmium exceeded 2 µg/g dw in six species, chromium in all but three, and lead surpassed 4 µg/g dw in Great Cormorants, with marginal exceedances in four others. These levels raise ecological concerns, suggesting potential adverse effects on waterbird health and reproductive success. The study highlights the importance of continued monitoring and assessment of trace metal burdens in waterbird populations to inform conservation strategies and protect these vulnerable species. The research emphasizes the need to understand the complex interplay between habitat contamination, trophic exposure, and waterbird diversity, echoing the importance of biodiversity-ecosystem functioning (BEF) relationships for effective habitat conservation[4].

WildlifeEcologyMarine Biology

References

Main Study

1) Effect of taxonomy and feeding guilds on waterbirds of the Southern Caspian Sea, Iran

Published 26th February, 2026

https://doi.org/10.1371/journal.pone.0334915

Related Studies

2) An integrated model for assessing heavy metal exposure risk to migratory birds in wetland ecosystem: A case study in Dongting Lake Wetland, China.

https://doi.org/10.1016/j.chemosphere.2015.03.053

3) The role of earthworm Lampito mauritii (Kinberg) in amending lead and zinc treated soil.

https://doi.org/10.1016/j.biortech.2007.12.079

4) Wetland habitats supporting waterbird diversity: Conservation perspective on biodiversity-ecosystem functioning relationship.

https://doi.org/10.1016/j.jenvman.2024.120663


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