PLANT PHENOLOGY AND THE BENEFITS OF MIGRATION IN A TEMPERATE UNGULATE

Seasonal changes in crude protein content of graminoids and herbs grazed by red deer were monitored from 1 May, or as soon as snow melt exposed the vegetation, until 15 October at five sites along an altitudinal gradient from coast to inland. Crude protein declined exponentially with time at all sites, but declined most rapidly from initially higher values at inland locations at high elevations. As a result crude protein was positively correlated with altitude and distance from the coast in early summer and negatively correlated in autumn. The relationships between protein content, date and altitude were used to estimate the quality of the diet of twelve radio-collared female red deer that migrated to summer ranges in the mountains. Individual differences in body weight were significantly related to the estimated, mean crude protein in vegetation available during the summer. Constraints on the timing of migration to exploit the maximal protein concentrations at higher altitudes and the fitness benefits of adaptive ranging behaviour are discussed.