We tested the hypothesis that tannins defend plants against large herbivores by decreasing protein availability. Digestion trials were conducted with mule deer (Odocoileus hemionus) and results from previous trials with white—tailed deer (O. virginianus), moose (Alces alces), caribou/reindeer (Rangifer tarandus), and elk (Cervus elaphus) were summarized to evaluate dietary factors affecting protein availability. The digestibility of plant protein in feeds with minimal tannins, such as grasses and agriculturally produced legumes and grains, was a highly predictable function of the total protein content and the amount of nondigestible, fiber—bound protein. Digestible protein in plants containing significant tannins was lower than predicted from regressions for low—tannin feeds. The reduction in digestible protein was proportional to the protein—precipitating capacity of the plant tannins. Deciduous browse stems collected in winter had very low levels of protein—precipitating tannins and only a slightly lower protein availability than predicted. Tannins are not important in the defense of most deciduous tree shrub stems consumed by these herbivores. Tannins in flowers and forb, tree, and shrub leaves markedly reduced protein availability. Tannins must be considered in understanding the defensive strategies of leaves and flowers. Voluntary intake of the high—phenolic forages was significantly reduced below ingestion rates for grasses, legumes, and pelleted diets. It is hypothesized that soluble phenolics that do not inhibit digestion but are absorbed and reduced intake through their toxicity are more important in defending some plant parts against ruminants than are digestion—reducing tannins.

Gestation in white-tailed deer (Odocoileus virginianus) of northern regions occurs throughout winter, when foragequantity and quality are limited. Our objective was to measure the energy cost of gestation during winter and spring in order todetermine its impact on energy balance of deer. We used indirect respiration calorimetry to measure the metabolism of 21pregnant deer every 2–4 weeks during gestation (January–May). Fasting metabolic rates (FMR) were used to develop apredictive equation to evaluate temporal energy costs. A measurable increase in metabolism occurred on day 91 of gestation.FMR (kJ/kg body mass (BM)0.75 per day) of pregnant deer rose curvilinearly (FMR = 0.02(days)2 – 3.261(days) + 465.2), with92.2% of the increase occurring in the third trimester; costs were 45% greater in the last trimester for pregnant than fornonpregnant deer. Peak FMR of pregnant deer at 200 days gestation was 617 kJ/kg BM 0.75 per day, 84% above that ofnonpregnant deer (335 kJ/kg BM 0.75 per day). The total energy cost of gestation, in terms of FMR, was 78 004 kJ/kg BM 0.75 per200 days, a 16.4% increase above that of nonpregnant deer. The temporal increase in energy costs was correlated with springgreen-up, indicating important relationships between energy demands, food quality and availability, spring weather, andphysiological adaptations in deer.

STAPP, P., PEKINS, P. J., and MALrrZ, W. W. 1991. Winter energy expenditure and the distribution of southern flying squirrels.Can. J. Zool. 69: 2548-2555. The southern flying squirrel (Glaucomys volans) forms large aggregations inside nest-lined tree cavities to reduce exposure to winter temperatures. We measured oxygen consumption of individuals and grouped flying squirrels in Plexiglas and nest-box chambers in New Hampshire to determine savings provided by huddling and nest construction. Because G. volans breeds during late winter, we also measured energy expenditure of females during gestation and lactation. These data were used to construct daily energy budgets for flying squirrels during winter and to investigate the relationship between this species' cold tolerance and its current distribution. Flying squirrels had lower basal metabolism (0.95 cm3 0,. g-' . h-') and rate of heat loss (0.1 1 cm3 0,. g-' . h-' . "c-') than predicted according to mass. Peak reproductive costs (1 week postparturition) were 170% of nonbreeding requirements. At 9°C huddling in groups of three and six reduced energy expenditure by 27 and 36%, respectively. Compared with individuals without nests, nest insulation decreased heat loss by 37% for single squirrels and reduced lower critical temperature from 26.5 to 12.2"C for groups of six. As estimated from our budget, aggregating reduces winter daily energy expenditure by 2633%. At the northern range boundary, daily expenditure for squirrels using both aggregations and nests (2.5 times basal metabolism) and for females during peak lactation (3.9 times basal metabolism) was similar to estimates of maximal daily energy expenditure in the literature. We speculate that additional thermoregulatory costs and the decreased abundance of hard mast for winter caches prevent G. volans from occupying areas north of its current distribution. STAPP, P., PEKINS, P. J., et MAUTZ, W. W. 1991. Winter energy expenditure and the distribution of southern flying squirrels.Can. J. Zool. 69 : 2548-2555. Les Petits Polatouqhes (Glaucomys volans) font des nids dans des cavitCs d'arbres et y fo'rment de grands rassemblements, ce qui a pour effet de rCduire leur exposition aux tempkratures de l'hiver. Nous avons mesurC la consommation d'oxygkne d'individus et de rassemblements dans des enceintes en Plexiglas et des boites h nids dans le but de dCterminer les Cconomies relikes h l'entassement et h la construction des nids au New Hampshire. Parce que G. volans se reproduit h la fin de l'hiver, nous avons aussi mesurC la dCpense CnergCtique des femelles au cours de la gestation et de la lactation. Ces donnCes ont servi par la suite h calculer le budget CnergCtique quotidien des polatouches durant l'hiver et h Ctablir la relation entre la tolCrance au froid de ces animaux et leur rkpartition gkographique actuelle. Les polatouches ont un mCtabolisme de base (0,95 cm3 0, -g-' . h-') et un taux de perte de chaleur (0,ll cm3 0, -g 1 . h-' "c-') plus faibles que les valeurs thCoriques calculCes d'aprks leur masse. Les c...

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