Predicting Early Mortality of Newborn Guanacos by Birth Mass and Hematological Parameters: A Provisional Model

Abstract

We measured hematological determinants, endocrine parameters, and birth mass of 145 newborn (chulengo) guanacos (Lama guanicoe) in Torres del Paine National Park, Chile, to determine if these factors were predictors of early mortality. Within 10 days of life, 16% of chulengos died in 1991 and 14% died in 1992. The principal cause (68%) of chulengo mortality was predation by the Patagonian puma (Felis concolor patagonia), but the role of compromised health was unknown. We assessed the health status of hand-captured chulengos by measuring white blood cell (WBC) count, differential leukocyte count, neutrophil:lymphocyte ratio (N:L), metarubricyte count, cortisol levels, total T3 and T4, and birth mass. We evaluated the prognostic relation of these parameters on neonatal mortality through Chi-square and Bayesian analyses. Band neutrophil count >1000/μL, lymphocyte count >4000/μL, N:L ratio 300/μL, and birth mass 1000/μL (suggestive of sepsis) showed signs of puma predation, while 100% (4/4) with an N:L ratio <2.0 (possible prematurity) showed signs of puma predation. The hematological parameters showing the strongest relation with mortality were also some of the least expensive and easiest parameters to measure. Readers should consider this Bayesian model groundwork for future studies assessing health-related neonatal mortality in guanacos. The approach also has research and management implications for other wildlife species.