Wild Bird Eggs Reveal Pollutants' Environmental Footprints

Monitoring the eggs of wild birds like the bearded vulture and the imperial eagle over a decade reveals the accumulation and persistence of environmental pollutants in ecosystems.

At first glance, a wild bird's egg represents the continuity of the species. However, it can also serve as a chemical reservoir, offering a broad snapshot of the environmental health of the bird's habitat.

Following this philosophy, the Veterinary Toxicology group (AGR-125) at the University of Córdoba, part of the UCO's Competitive Research Unit for Zoonoses and Emerging Diseases (ENZOEM), collaborated with the Andalusian Center for Wildlife Analysis and Diagnosis (CAD) to monitor the eggs of 14 bird species over a decade. The aim was to characterize how wild birds are exposed to environmental pollutants.

From a One Health perspective, according to which environmental, human, and animal health are interconnected, this study goes beyond simply detecting contamination in eggs to determine its implications for birds. As Nahúm Ayala, a Veterinary Toxicology researcher and the study's leader, explained: "Using eggs as a tool for biomonitoring gives us an overview that lets us determine which pollutants are circulating in ecosystems."

Analyzing unhatched eggs collected from natural environments between 2014 and 2024 detected the presence of contaminants derived from DDT, the pesticide banned in the 1970s due to its harmful effects on human health and ecosystems. In addition to these well known pollutants, which still endure half a century after their ban, they also identified residues of currently used pesticides and fungicides.

"These types of contaminants directly impact the reproduction of species like the bearded vulture, which lays only one or two eggs per year, making reproductive failure a significant concern. The presence of DDT, for example, is linked to a thinning of the eggshell, which makes it more susceptible to the entry of microorganisms, and moisture loss, thereby jeopardizing the egg's," explained Isabel Fernández, a CAD researcher and the study's lead author.

In this case, the eggs underwent a detailed examination that included biometric measurements, an assessment of embryonic development, and an investigation into possible causes of their reproductive failure. This was complemented by chemical analyses of the shells and egg contents to analyze the various contaminants.

All the potential an egg contains

Data from these types of studies are crucial in the field, "as they provide highly valuable information for managing natural areas and species under conservation programs, and are also essential for detecting emerging contaminants early," Nahúm Ayala said.

Birds of prey, one of the most represented groups in this study, occupy the highest levels of the food chain. Therefore, the presence of these pollutants in their eggs serves as evidence of how they accumulate and persist in the environment.

This work, which falls within the research group's focus on wildlife biomonitoring, will pave the way for future research on the presence and accumulation of emerging contaminants of environmental concern, such as microplastics, by using wildlife as sentinels of the health of the environments they inhabit.

Reference:

Fernández-Verón I, Mora-Medina R, Zorrilla-Delgado I, Lora-Benítez AJ, Molina-López AM, Moyano-Salvago R, Ayala-Soldado N. Wild bird eggs as bioindicators of environmental contamination: A decade of xenobiotic monitoring in Spain. Ecotoxicol Environ Saf. 2026 Apr 1;314:120009. doi: 10.1016/j.ecoenv.2026.120009