Variación del nitrógeno fecal de Odocoileus virginianus a diferentes tiempos de exposición ambiental

Abstract

Introduction: Successful wildlife management requires reliable indicators of the nutritional status of the animals in order to assess the relationship between them and their habitat. Fecal nitrogen (FN) has often been considered to be a good indicator of diet quality. FN analysis has been applied extensively in the temperate region of the range of the deer Odocoileus; however, little is known about the usefulness of this approach in the tropical habitats where the white-tailed deer O. virginianus is hunted. This study presents data on the variation in FN concentration with increased time of exposure. Specifically, we discuss the implications for field sampling in tropical habitats where environmental conditions can rapidly degrade deposited deer feces.Methods: Quantification of FN was performed with 18 freshly deposited pellet-groups collected at the end of the dry season of 2008 (April-May) in a protected natural area in Puebla state, Mexico. Samples were transported frozen to a Botanical Garden in Xalapa, Veracruz, where they were kept under controlled environmental conditions. Each pellet-group was sampled every 15 days, up to 60 days, by which time most of the droppings were covered with fungi due to the high humidity at the site. FN concentration was determined according to the micro-Kjeldahl method. An analysis of variance for repeated measures to detect differences in FN considering the deposition time and fecal groups as factors was applied using lm function in R.Results: FN varied significantly depending on the exposure time of the feces. The initial concentration was 2.29 mg/ml and this value remained constant for 15 days, subsequently decreasing to a minimum of 0.019 mg/ml, which was reached 60 days after the start of the experiment.Discussion and Conclusions: The use of fecal indexes may be a feasible non-invasive method by which to study diet quality, and an alternative to other techniques that imply disturbance, stress, or death of wild ungulates. In addition, fecal index is inexpensive and easy to apply on large sections of wild animal populations, throughout the year. Our results suggest that use of this method can give reliable results relating to white-tailed deer FN for up to two weeks post-defecation. In contrast, the results of another study suggest that feces collected for up to 24 days post-defecation, in September/October in temperate habitat in US, can be used to estimate FN as well as other nutritional characteristics. Seasonal variation in environment conditions and diet composition could explain these differences. We therefore recommend cleaning permanent sample plots and then returning to locate and collect fresh droppings within these plots.Key words: fecal nitrogen, nutritional quality, Odocoileus virginianus, tropical habitats.