CHAPTER XIX – Energy Metabolism, Thermoregulation and Body Temperature1

1.

Seasonal variation in body constituents and utilization of lipid, protein, and carbohydrate during cold stress in American goldfinches were studied to determine relations of these functions to the pronounced seasonal shift in thermogenic capacity documented in a previous study (Dawson and Carey, 1976).




2.

Mean body mass for adults increases from a low of 11.4 g in July to a high of 15.1 g in December and January. Seasonal variation in lipid content accounts for the major part of the observed changes in body mass, but such variation in water and protein content is also appreciable.




3.

Linoleic acid (18∶2) is the predominant fatty acid in neutral lipids of liver, pectoralis muscle, and furcular depots at all seasons. Unsaturated fatty acids comprise a much greater proportion of total fatty acids in liver and pectoralis muscle during winter (71% and 73%, respectively) than in spring or fall.




4.

Fasting winter goldfinches exposed to −10°C for 17 h overnight utilize significant amounts of body lipid. However, total body protein, liver and pectoralis muscle carbohydrate, and pectoralis muscle fatty acids do not differ significantly between control and cold-stressed individuals.




5.

Glycogen stores in the pectoralis muscles are significantly higher in winter than in summer birds. Winter goldfinches exposed to −70°C utilize significant amounts of total body lipids and pectoralis glycogen. Birds tested in this manner in summer do not do so and quickly become hypothermic.




6.

Histochemical characteristics and succinate oxidase activities of pectoralis muscles do not vary appreciably over the year.




7.

Increased stores of body lipid and muscle carbohydrate and the ability to mobilize these substrates rapidly during cold stress seem to be key factors in the superior thermogenic capacities of winter goldfinches.

/pdf/seasonal-acclimatization-to-temperature-in-cardueline-1wohik5rs5.pdf

Seasonal acclimatization to temperature in cardueline finches

Birds are found on every continent and in or above the surrounding seas. With the wide distribution of the group, many of its members encounter challenging thermal conditions, even though migratory movements afford certain species opportunities for evading winter or summer extremes. The thermoregulatory processes that contribute to birds’ maintaining homeostasis in the face of these conditions have received considerable attention (see, e.g., Calder and King 1974; Dawson 1984; Whittow 1986; Marsh and Dawson 1989). We shall explore a different pathway in this review, emphasizing the energetic costs of these processes, that is, the costs of heat and cold defense in normothermic birds. These activities are complicated for many species by small size. The vast majority of birds weigh less than 100 g and many are smaller than 10 g. Such masses involve low thermal inertia and narrow zones of thermal neutrality (cf. Calder and King 1974, pp. 278-279). In the ensuing discussion, we shall strive to integrate laboratory and field observations to make our considerations as ecologically relevant as possible.

Energetic Features of Avian Thermoregulatory Responses

In White-crowned Sparrows wintering in southeastern Washington, there is an inverse correlation between the quantity of body fat and mean air temperature below about 3 C. Between 3 C and 9 C the fat reserves are independent of air temperature. Because of seasonal variation in fat-free body weight in this species, variation in total body weight is not a highly reliable index of variation in lipid reserves. A review of published data indicates that winter fattening is a common phenomenon in small birds which winter in cold habitats or high latitudes, although exceptions can be found in species that evidently in part substitute behavioral adaptations for winter fattening. It may be concluded provisionally that the magnitude of winter fattening tends to be less inwarmer habitats or at lower latitudes.It is absent in a subequatorialwintering population of Yellow Wagtails. Although it is reasonable to assume that winter fattening is an adaptation to the thermoregulatory demands of low ambient temperature, the t...

The Adaptive Role of Winter Fattening in the White-Crowned Sparrow with Comments on its Regulation

Thermoregulatory responses of the peruvian penguin, Spheniscus humboldti.

Pigeons were kept at different air temperatures while measurements were taken of the temperatures in various parts of their bodies. At room temperature the abdomen and the pectoral muscles had nearly the same temperature. At –22°C the pectorals stayed one-half to two degrees warmer than the abdomen, which remained the same as at room temperature. Myograms from the pectorals showed a considerable electrical activity in the cold which vanished at room temperature. It is concluded that the increased pectoral temperature reflects an elevated heat production. As the pectorals of a pigeon make up about one-third of the body weight, it is clear that they make a significant contribution to the accessory heat during cold stress.

Muscular heat production in pigeons during exposure to cold.

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Muscular heat production in pigeons during exposure to cold.