Environmental stressors, particularly agricultural pesticides, can influence both growth and physiology in developing birds, yet the relationship between morphometric condition indices and biochemical biomarkers remains poorly understood. We investigated body mass, beak length, tarsus length, and body condition index (BCI) alongside plasma and S9 biomarkers, including the activities of acetylcholinesterase (AChE), carboxylesterase (CES), and glutathione S-transferase (GST), as well as the levels of glutathione (GSH) and reactive oxygen species (ROS) in nestling White Storks (Ciconia ciconia) from Croatia. Bayesian undirected graphical model (BUGM) inferred a disconnected correlation structure composed of two communities, with a strong beak length–GSH association. Biomarkers further exhibited plasma-specific affinity: plasma markers reflected short-term adjustments, whereas S9 enzymes represented distinct metabolic pathways. Overall, morphometry and physiological status showed only limited integration, restricted mainly to plasma biomarkers, and residual body condition index did not serve as a reliable proxy for physiological stress. We conclude that integrated monitoring approaches, combining morphometric and biochemical profiling, provide a more nuanced assessment of nestling condition and strengthen the use of White Storks as sentinels of agroecosystem health.

Landfills represent increasingly common anthropogenic habitats that provide food resources but also expose wildlife to complex chemical mixtures. White Storks (Ciconia ciconia) have recently expanded breeding near such sites, yet little is known about the physiological consequences of landfill dependence across time. In 2025, we assessed biomarker responses in White Stork (Ciconia ciconia) nestlings from the Jakuševec landfill (Zagreb, Croatia), a post-remediated site still in partial operation, three years after the initial studies conducted in 2021 and 2022. Activities of acetylcholinesterase (AChE), carboxylesterase (CES), glutathione S-transferase (GST) and glutathione reductase (GR), as well as levels of reduced glutathione (GSH) and reactive oxygen species (ROS), were quantified in extracellular (plasma) and intracellular (post-mitochondrial S9) blood fractions. Neurotoxicity biomarkers (AChE, CES) showed small increases in 2022, followed by significant declines in 2025, indicating potential changes in exposure to neuroactive compounds. Oxidative-stress biomarkers displayed contrasting patterns: GST and GR decreased progressively, whereas ROS rose and GSH shifted in opposite directions between fractions, together suggesting rising oxidative challenge and altered redox balance. The combined biomarker response suggests continuing low-level exposure to neurotoxic and redox-active compounds despite landfill remediation. Our findings highlight that urban landfills, even in post-closure phases, remain physiologically active systems influencing wildlife health and should be incorporated into long-term ecotoxicological and conservation monitoring frameworks. While independent long-term monitoring shows that the Jakuševec White Stork colony has continued to grow over the past decade, the physiological responses detected in nestlings highlight the importance of assessing how chronic low-level exposure might influence population health in the long term.

Trace metals and metalloids pose persistent threats to freshwater ecosystems, yet their trophic transfer and sublethal effects across food webs remain poorly understood. We investigated bioaccumulation patterns and biomarker responses in a predator–prey system comprising Prussian carp (Carassius gibelio) and Great Cormorant (Phalacrocorax carbo) nestlings from the Danube floodplain wetland Kopački rit Nature Park (Croatia) during 2023–2024. Concentrations of arsenic (As), selenium (Se), cadmium (Cd), mercury (Hg) and lead (Pb) were determined in Prussian carp liver and in Great Cormorant whole blood. The activities of acetylcholinesterase (AChE), carboxylesterase (CES), glutathione S-transferase (GST) and the levels of reactive oxygen species (ROS) and reduced glutathione (GSH) were measured in brain, muscle and gill tissues of Prussian carp, as well as in plasma and S9 blood fractions of Great Cormorants. In addition, tissue-specific metal concentration ratios (TSMCR) were calculated to assess the relative magnitude of recent dietary exposure in the predator compared to the prey. Biomarker activity showed strong tissue- and fraction-specific variation, with temporal differences. Exposure–response modelling revealed significant associations between As, Cd, and Hg and specific biomarkers, particularly in gill and plasma. Cross-species comparisons indicated elevated TSMCR as a proxy for recent trophic exposure only for Hg in 2023, whereas As and Se exhibited lower TSMCR. These findings demonstrate that metal exposure in floodplain systems induces physiological responses and Hg poses the greatest prey-to-predator exposure risk, highlighting the value of integrating pollutant measurements with mechanistic biomarker endpoints to evaluate ecosystem-level impacts.