Energy Allocation by Yellow-Bellied Marmots

Abstract

Energy intake, daily energy expenditure (DEE), and energy available for production were determined for yellow-bellied marmots (Marmota flaviventris) at three study sites in the Elk Mountains of southwestern Colorado. Energy intake, estimated from tritiated-water turnover rates and the water and energy content of food plants, ranged from 3,283 kJ d⁻¹ for two lactating females in July to 666 kJ d⁻¹ for a yearling female in September. Maintenance, activity, and thermoregulatory components of DEE were estimated from time-budget data, estimated or measured activity costs, and heat-transfer theory. Not including energy allocated to production, DEE ranged from 1,017 kJ d⁻¹ for a lactating female in July to 539 kJ d⁻¹ for a female yearling in June. Time spent in the burrow accounted for 41%-60% of DEE; foraging, for 11% -51%; sitting on rocks by the burrow, for 1%-28%; and thermoregulation, for 1%-6%. Assimilated energy exceeded DEE for all but one animal studied; mass gains calculated assuming that assimilated energy in excess of DEE was available for production closely matched average measured mass gains of field animals.