The energetics of autumn mast hoarding in eastern chipmunks

Abstract

The timing and basis of the transition from energy reserve accumulation to reserve utilization in autumn may be a key determinant of winter survival in endotherms, but has rarely been examined directly in the field. In the present study we quantify the energetics of autumn mast hoarding in eastern chipmunks (Tamias striatus) to document the degree to which larder hoarding permits capitalizing on brief pulses of resource abundance and to evaluate the basis of the decision to stop hoarding and initiate hibernation. Daily energy expenditure, measured with the doubly labeled water technique, increased significantly with date and decreasing ambient temperature, eventually exceeding 3× resting metabolic rate in late autumn. Simultaneous documentation of food delivery to burrow larder hoards revealed that delivery rates were low in early autumn, extremely high for a brief period in mid-autumn, then low again in late autumn. Combining estimates of energy expenditure, consumption, and delivery yielded net energy surpluses of 1,320-4,600 kJ day(-1) during the peak hoarding period, meaning total hibernation energy requirements could be acquired in 1-2 days. These results, together with measures of food availability and ambient temperature, suggest that chipmunk activity in late autumn may be affected by both the extent of hoard accumulation and thermoregulatory constraints on sustained energy expenditure. We speculate that both state-dependency and energetic ceilings on autumn hoarding behavior may enhance the capacity of the mast seeding strategy of trees to effectively swamp the foraging efforts of larder-hoarding granivores.

Daily energy expenditure in the face of predation: hedgehog energetics in rural landscapes

“…In 2013, energetics experiments went on later into September, and during the autumn hedgehogs forage intensively to increase fat stores for hibernation (Dowding et al, 2010;Haigh et al, 2012). Rates of foraging result in high energy expenditure (Bryce et al, 2001;Humphries et al, 2002) and we surmise that we only captured the effects of intensive autumn foraging in 2013.…”

Context-dependent correlation between resting metabolic rate and daily energy expenditure in wild chipmunks

“…This technique provides an accurate measure of DEE over periods of several days in small mammals and has previously been used successfully on eastern chipmunks (Humphries et al, 2002). The dataset used in this study is a subset (i.e.…”

“…Autumn is a critical period for chipmunks as they must actively forage to accumulate enough energy for winter (Humphries et al, 2002), which is associated with high energy expenditure in other rodents (Fletcher et al, 2012). Thus, in both mast and nonmast years, increased RMR in autumn may support the metabolic demands imposed by the combination of increased foraging effort and increased cold exposure experienced at this time of year.…”

The evolution of body fatness: trading off disease and predation risk

“…However, much less energy can be stored internally than in external caches. For example, in autumn, the chipmunk (Tamias striatus), which relies principally on stored acorns to survive the winter, can deposit up to 4600 kJ day − 1 of acorns into its winter cache (Humphries et al, 2002). This process is repeated for many days in a row, creating a cache containing potentially 10× this amount.…”