<p>In this study, we evaluated hematological and plasma biochemical metrics in kelp gulls (<i>Larus dominicanus</i>) using an open-air landfill in Mar del Plata, Argentina, across two wintering seasons. Forty-nine gulls were captured during the winters of 2022 and 2023, and hematological and plasma biochemical parameters was analyzed. In general terms, hematological and biochemical values were broadly consistent with previous reports for <i>Larus</i> gulls that exploit anthropogenic food sources, such as fishery discards and urban waste. However, marked interannual, sex-, and age-related differences were detected, likely reflecting physiological variation associated with environmental conditions, dietary differences, or differential exposure to anthropogenic stressors. Males had lower globulins (and higher albumin-globulin ratio) than females. Adults had higher eosinophils and triglycerides than immatures. Total leukocyte counts were lower than in other populations but remained within physiological limits, with elevated heterophil and lymphocyte proportions indicating maintained immune function. Subtle shifts in immune and metabolic indicators, including reduced albumin-globulin ratios and elevated glucose, cholesterol, and triglycerides, suggesting physiological adjustments associated with the use of urban-derived food resources. These findings provide baseline health information for kelp gulls in urban-modified habitats, underscoring their ecological plasticity and the need for integrative monitoring, including contaminants, hormonal profiles, and oxidative stress markers, to assess the long-term effects of urbanization on coastal seabirds.</p>