Bite characteristics of wapiti (Cervus elaphus) in seasonal Bromus-Poa swards

Abstract

We used a cubic sampling quadrat to study the 3-dimensional structure of volunteer Bromus-Poa swards, and explored the relationship of bite depth and sward height as a determinant of bite sizes of wapiti (Cervus elaphus) in the mixed-wood parklands of central Alberta, Canada. The vertical biomass distribution of the sward was pyramidal with leaves dominating the top stratum. Bite depths of yearling and adult wapiti were not significantly different but both were influenced by sward height and season. Wapiti selected bites in both vertical and horizontal dimensions. In spring, wapiti selected vertically, taking green leaves in the top layer of the sward. They selected forbs horizontally in summer and selected leaves vertically in mature autumn swards. Based on the relationships among bite depth and sward height, biomass and sward height, as well as vertical biomass distribution, we calculated expected bite sizes of wapiti on seasonal pasture. We also predicted changes of dietary protein and neutral detergent fiber with increasing bite depth. On spring swards, calculated dietary protein decreased and fiber increased as animals grazed deeper into the swards. In summer and autumn, dietary protein peaked as wapiti cropped about half of the height of the sward whereas dietary fiber was relatively constant. Wapiti adjusted their bite depth to select forage containing at least 14% protein in spring, summer, and autumn. The sacrifice of bite size in tall summer and autumn swards was compensated by diet quality.