Is summer food intake a limiting factor for boreal browsers? Diet, temperature, and reproduction as drivers of consumption in female moose

Food intake may limit the ability of browsing mammals to gain body mass during the growing season when the leaves and stems of woody plants are most abundant. Moose are highly productive browsers with high demands for energy and nutrients, particularly during lactation. Using an indigestible marker, we estimated dry matter intake of free ranging adult female moose with and without calves over three growing seasons. During the same period, we analyzed forage quality. Intakes were highest in late spring (280 ± 19 g·kg-0.75·d-1) when forage quality peaked; however, intakes declined by 39% throughout the summer as temperatures increased and as acid detergent fiber content of browse increased. Digestibility of dry matter declined over summer from 71% to 57% among browse. Intakes were similar for moose with and without calves. Heat loads may impair the ability of moose to consume sufficient energy and nutrients. Warming and habitat change can adversely affect browser populations when poor forage qualities and low dry matter intakes combine to suppress digestible intakes of energy and nutrients.

在木本植物枝叶最为繁茂的生长季，食物摄入可能限制啃食型哺乳动物的体重增长能力。驼鹿作为高生产力的啃食者，对能量与营养物质有着较高需求，尤其在泌乳期。本研究利用不可消化标记物（indigestible marker），估算了三个生长季中，野外自由活动的带崽与不带崽成年雌性驼鹿的干物质采食量（dry matter intake）。同期，我们还对饲草品质进行了分析。
晚春时节饲草品质达到峰值，此时驼鹿采食量最高，为280 ± 19 g·kg^-0.75·d^-1；但整个夏季，随着气温升高以及所啃食植物的酸性洗涤纤维（acid detergent fiber）含量上升，采食量下降了39%。夏季期间，所啃食饲草的干物质消化率从71%降至57%。带崽与不带崽的驼鹿采食量无明显差异。
热负荷可能会削弱驼鹿摄入足够能量与营养物质的能力。当饲草品质不佳与干物质采食量偏低共同抑制了可消化的能量与营养摄入时，气候变暖和栖息地变化可能会对啃食型哺乳动物种群产生不利影响。