Descriptive hematologic intervals and intrinsic drivers of variation in the costa rican endemic cabanis’s ground sparrow ( Melozone cabanisi )

Hematological parameters are widely used as integrative indicators of physiological condition in birds. The Cabanis’s Ground Sparrow (Melozone cabanisi), a Costa Rican endemic species commonly associated with coffee plantations and semi-modified landscapes, lacks baseline hematological information, limiting the interpretation of blood-based health assessments. In this study, we established descriptive hematologic intervals for M. cabanisi and evaluated the influence of intrinsic biological factors—pectoral muscle condition and molt stage—on hematological variation. Free-ranging individuals were captured using mist nets and processed following standardized protocols. We quantified erythrocyte, leukocyte, and thrombocyte parameters, plasma protein concentration, and erythrocyte indices. Mean corpuscular hemoglobin concentration (MCHC) was selected as a focal parameter to assess physiological condition. Effects of muscle condition and molt stage on MCHC were evaluated using ART ANOVA and complementary bootstrapped linear models. Hematological values for M. cabanisi were broadly consistent with those reported for other small passerines, indicating conserved erythrocytic and immunological profiles. Pectoral muscle condition emerged as the strongest predictor of MCHC, with individuals in better somatic condition exhibiting significantly higher values. In contrast, molt stage did not show a significant main effect on MCHC in conservative analyses, and no interaction between muscle condition and molt stage was detected. These results provide the first hematological reference intervals for M. cabanisi and highlight body condition as a key intrinsic driver of hematological variation. The reference values presented here offer a robust physiological baseline for future ecological, conservation, and wildlife health studies involving this endemic Neotropical passerine.