The effect of forage structure and availability on food intake, biting rate, bite size and daily eating time of reindeer

Trudell, Jeanette; White, Robert

(1) Factors influencing the food intake of reindeer (Rangifer tarandus tarandus L.) on tundra were studied using tame animals. Food intake was estimated from 2 to 5-mm collections of oesophageal fistula egesta: biting rate was measured concurrently. Food intake depended on plant species, growth form, and available plant biomass. When corrected to a constant biomass (50 g.m$^{-2}$), the ranking of eating rate was forbs (13 g.min$^{-1}$) > Salix spp. and Eriophorum vaginatum (6 g.min$^{-1}$) > Carex spp., Betula nana and lichens (3-4 g.min$^{-1}$). However, food intake increased linearly with standing crop for all growth forms except forbs which were eaten rapidly even when scarce. At peak standing crop, single-stemmed graminoids and carpet shrubs were ingested at 2$\cdot$4-3$\cdot$6 g.min$^{-1}$, tussock graminoids and tall shrubs at 5$\cdot$3-6.9 g.min$^{-1}$ and forbs and lichens at 5$\cdot$9-12$\cdot$7 g.min$^{-1}$. (2) Prehension patterns were found to differ by plant growth form. A significant difference (P < 0.001) was found between bite rate and bite size when vascular plants (177 $\pm$ 3 bites.min$^{-1}$, 21 $\pm$ 1 mg.bite$^{-1}$) and lichens (205 $\pm$ 5 bites.min$^{-1}$, 32 $\pm$ 4 mg.bite$^{-1}$) were ingested. Bite rate increased by 4.6 bites.min$^{-1}$ per 100 g.m$^{-2}$ increase in biomass of total vascular plants, by 21 bites.min$^{-1}$ per 100 g.m$^{-2}$ increase in biomass of vascular plant parts selected for, and by 28 bites.min$^{-1}$ per 100 g.m$^{-2}$ increase in biomass of the highly preferred shrub Salix pulchra. No significant correlation was found between bite rate and biomass of lichens. For the graminoids Carex aquatilis and Eriophorum vaginatum, a significant positive correlation was found between bite rate and food intake (P < 0.05) and a similar trend was noted for all vascular plants combined. In contrast, there was a negative trend between bite rate and food intake of lichens. Bite size was not correlated with total live biomass, selected vascular plant biomass, or biomass of lichens. On a daily basis, time spent grazing and eating decreased at the respective rates of 1$\cdot$6 $\pm$ 0$\cdot$05 h and 1$\cdot$3 $\pm$ 0$\cdot$1 h for each 100 g.m$^{-2}$ increase in total plant (vascular + lichen) biomass. Reindeer biting rates were much greater than those of sheep and cattle and the results suggest that a high bite rate and small bite size may favour forage selection while grazing.

The effect of forage structure and availability on food intake, biting rate, bite size and daily eating time of reindeer

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