William R. Dawson

A Re-Examination of the Relation between Standard Metabolic Rate and Body Weight in Birds

An exponential relation exists between standard energy metabolism and body weight in organisms that is described by the generalized equation: Metabolic Rate = a (Body Weight) b (a) where a and b are empirically derived constants. This equation can be rewritten in the more convenient logarithmic form: log Metabolic Rate = log a + b log Body Weight (b) recognizable as a mathematical expression of a straight line. Hemmingsen (1950, 1960) has reviewed the relation of energy metabolism to body size in all organisms, and argues that a b-value of 0.75 best describes the existing data for unicellular organisms, plants, poikilothermal and homeothermal animals. However, the observed limits of b are 0.63-1.0 among individual groups (Zeuthen, 1953, and others). Despite recent increased interest in avian bioenergetics, a definitive statement concerning the relationship between metabolic rate and body weight in birds has been lacking. Several formulas for this relationship have been presented. Brody and Proctor (1932) fitted the following equation to data on avian body weight and metabolism: log M = log 89 + 0.64 log W (c) where M is in kcal/day and W is in kilograms. This expression, in which the regression coefficient (b) of 0.64 differs markedly from those obtained from mammals (0.73-0.76) by Brody and Proctor (1932), Kleiber (1932, 1947), Benedict (1938), and Brody (1945), has been generally accepted for birds until recently. King and Farner (1961) have commented that “on theoretical grounds there seems to be no reason to believe a priori that the relationship of metabolic rate and body weight should be very different in the homoiotherm classes.” With many more metabolic values than were available previously, King and Farner re-analyzed the relationship, using more rigorous criteria for including data in their computations. They obtained the following equation: log M = log 74.3 + 0.744 log W * 0.074. (d) King and Farner believe that this equation is superior to that of Brody and Proctor (1932) in predicting the metabolic rates of birds weighing more than 0.1 kg. However, they concluded that it does not adequately portray the metabolism-weight relationship for smaller birds. Equation (d) is statistically indistinguishable from Kleiber’s (1947) equation for mammals, and it is therefore doubtful that the metabolism-weight relationship for birds weighing more than 0.1 kg really differs from that in mammals. King and Farner (1961) discuss the possibility that the avian relationship may be curvilinear in the lower ranges of body weight, since small birds have higher metabolic rates than predicted by their equation. Virtually all of the small birds (< 0.1 kg) are passerines, whereas all but two of the species weighing more than 0.1 kg belong to other orders. Dawson and Lasiewski have suggested (see Lasiewski, 1963 ; Lasiewski et al., 1964) that passerines as a group show the same weight-regression coefficient as nonpasserines, but have a higher metabolism per unit weight than nonpasserines of comparable size. Documentation of this suggestion required additional data on large passerines and small nonpasserines. Now that these are available, it is

Observations on the Thermal Relations of Western Australian Lizards

GOSNER, K. L. 1960. A simplified table for staging anuran embryos and larvae with notes on identification. Herpetologica 16:183-190. LYNN, W. G. AND B. LUTZ. 1946. The development of Eleutherodactylus guentheri Stdnr. 1864. I Notes on the external development of Eleutherodactylus guentheri. Biol. Mus. Nac., Rio de Janeiro, Zoologia 71:1-12. MAIN, A. R. 1954. Key to the frogs of SouthWestern Australia. Handbook No. 3, West. Aust. Nat. Club, Perth, W. A. ,A. K. LEE, AND M. J. LITTLEJOHN. 1958. Evolution in three genera of Australian frogs. Evolution 12:224-233. , M. J. LITTLEJOHN, AND A. K. LEE. 1959. Ecology of Australian frogs. Monogr. Biol. 8: 396-411. OSNER, K. L 1960. A simplified tabl for taging anuran embryos and larvae with notes identif cation. Herpetologica 16:18390. NN, W. G. AND B. LUTZ. 1946 The developent of Eleutherodactylus guentheri S dn . 864. I Notes on the external deve opment of leutherodactylus guenth ri. Biol. Mus. Nac., io de Janeiro, Zoologia 71:1-12. AIN, A. R. 1954. Key to the frogs of SouthMoORE, J. A. 1958. A new genus and species of leptodactylid frog from Australia. Am. Mus. Novit. 1919:1-9.

Seasonal acclimatization to temperature in cardueline finches

Summary1.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.

Evaporative losses of water by birds.

1. Birds lose water in evaporation from the respiratory tract and, in many species, through the skin. Anatomical arrangements in the nasal passages to conservation of water and hear from the expired air in the absence of heat loads. However, most species still expend more water in evaporation than they produce in metabolism when either quiescent or vigorously active. Certain small birds, several of them associated with arid environments, represent exceptions to this and their more favorable situation appears in part to reflect as an ability to curtail cutaneous water loss. 2. Birds typically resort to panting in dealing with substantial heat loads developing in hot environments or accumulated over bouts of activity. In a number of species this form of evaporative cooling is supplemented by gular fluttering. 3. The ubiquitousness of active heat defense appears to reflect more the importance for birds of dealing with heat loads existing following flight or sustained running than any universal affinity for hot climates. Panting can be sustained for hours, despite progressive dehydration and, in some instances, hypocapnia and respiratory alkalosis. The prominent involvement of thermoreceptors in the spinal cord in its initiation is of considerable interest.

Aerobic and anaerobic metabolism during activity in the lizardDipsosaurus dorsalis

Summary1.Oxygen consumption and lactate content of the lizardDipsosaurusdorsalis were determined under standard conditions and for a bout of maximal activity induced by a 2-min period of electrical stimulation. Observations were made between 25 ° and 45 °C.2.Maximal aerobic scope, 2.27 cm3 O2/(g × hr), occurred at 40 °C (Figs. 2, 4). The increase in oxygen consumption during activity at the various temperatures between 25 ° and 45 °C represented 7- to 17-fold of corresponding resting levels.3.Lactate content of restingDipsosaurus is independent of temperature and averages 0.25 mg/g body weight. Maximal lactate production during the activity induced by a 2-min period of electrical stimulation occurred at 40 °C (Fig. 3). The capacity ofDipsosaurus for anaerobic metabolism exceeds that of other lizards investigated, both in its magnitude and in its thermal dependence.4.The total amount of energy mobilized byDipsosaurus in the activity induced by a 2-min period of electrical stimulation was maximal at 40 °C (Fig. 4). Anaerobiosis accounts for a minimum of 58–83% of the total energetic expenditure.5.It is postulated that the principal physiological adaptations to preferred thermal levels in reptiles have involved energy mobilization during and rapid recovery after activity.

Relation of Oxygen Consumption to Body Weight, Temperature, and Temperature Acclimation in Lizards Uta stansburiana and Sceloporus occidentalis

BROWNE, W. R. 1945. An attempted post-Tertiary chronology for Australia. Proc. Linn. Soc. New South Wales, 70:v-xxiv. BURBIDGE, N. T. 1953. The genus Triodea R. Br. (Gramineae). Australian Jour. Bot., 1:121-84. CROCKER, R. L., and WOOD, J. G. 1947. Some historical influences on the development of the South Australian vegetation communities and their bearing on concepts and classification in ecology. Trans. Roy. Soc. South Australia, 71: 91-136.

The Relation of Oxygen Consumption to Temperature in Desert Rodents

No information is available on the effects of temperature upon the oxygen consumption of any desert rodent, although the Schmidt-Nielsens (1950 a ) have made measurements on several species at 25° C. in the course of their extensive investigations of water metabolism (1952). Accordingly, this study dealing with the Merriam and Panamint kangaroo rats ( Dipodomys merriami and D. panamintinus ) and with the antelope ground squirrel ( Citellus leucurus ) was undertaken. It attempts to define the zones of metabolic thermal neutrality for these desert animals, to analyse their metabolic responses to ambient temperatures above and below thermal neutrality, and to compare the temperature regulation of the nocturnal kangaroo rats, which do not meet the most intense desert heat, with that of the diurnal ground squirrel, which periodically encounters high air temperatures and intense solar radiation. This investigation was carried out during tenure of a U. S. Public Health Service Research Fellowship in the Department of Zoology, University of California, Los Angeles. I am grateful for the numerous courtesies extended by Dr. George A. Bartholomew in placing the facilities of his laboratory at my disposal. Materials and Methods .—Twenty-five Merriam kangaroo rats, 15 Panamint kangaroo rats, and 12 antelope ground squirrels were used in this study. All were captured during June and July, 1953, at Lovejoy Buttes, Los Angeles County, California, a site located near the western edge of the Mojave Desert. They were housed in glass terraria during their stay in the laboratory. Each terrarium had a sand-covered floor and was provided with a 16 oz. bottle made of brown glass, which afforded the animals a place of retreat. Cotton was available for nesting material. The antelope ground squirrels and Panamint kangaroo rats were housed individually. The more sociable Merriam kangaroo rats were placed several to a terrarium. Pood consisting of sunflower …

Roles of metabolic level and temperature regulation in the adjustment of Western plumed pigeons (Lophophaps ferruginea) to desert conditions

Abstract 1. 1. Standard metabolic rate of western plumed pigeons ( Lophophaps ferruginea ) averages 0·88 ml O 2 (g hr) −1 during summer. This rate and the rate of evaporative water loss by these birds at 25°C are well below levels anticipated for birds of comparable size (81 g). 2. 2. Summer and late fall birds did not have significantly different minimal thermal conductances, the means for both approximating 1·8 kcal (m 2 hr °C) −1 . 3. 3. A relatively low level of metabolism and effortless evaporative cooling restrict the caloric burden for western plumed pigeons in the hot and arid regions of northwestern Australia where these birds live. Other pigeons closely associated with hot and arid environments also have relatively low metabolic rates.

Physiological Responses to Temperature in the Common Nighthawk

The family Caprimulgidae contains species which appear to deviate from general avian patterns in certain aspects of their physiology. Lesser Nighthawks (CtcordeiZes acuti@nnis) and Poorwills (PhaZuenopti2us nuttallii) can remain torpid for relatively long periods in a manner reminiscent of hibernating mammals (Marshall, 19 5 5 ; Jaeger, 1949; Thorburg, 1953). Pauraques (Nyctidromus aZbicoZZis) and Poorwills have lower basal metabolic rates than most birds of comparable size (Scholander, Hock, Walters, and Irving, 1950; Bartholomew, Hudson, and Howell, 1962). Most or all members of this family employ gular fluttering in their evaporative cooling, and this contributes to an unusually effective capacity for temperature regulation in hot environments (see Cowles and Dawson, 1951; Howell, 1959; Bartholomew, Hudson, and Howell, op. cit.). Although these features make caprimulgids of special interest from a physiological standpoint, only the Poor-will has been subjected to extensive experimental investigation (Bartholomew, Howell, and Cade, 19.57; Bartholomew, Hudson, and Howell, op. cit.; Howell and Bartholomew, 1959). Since studies dealing with the physiology of additional species in this group appeared desirable, this investigation of the effects of ambient temperature on oxygen consumption, heart rate, evaporative cooling, and body temperature of the Common Nighthawk (Chordeiles minor minor) was undertaken. This species, which is abundant in southeastern Michigan in summer, might be expected to differ from the Poorwill in certain features of its physiology owing to its larger size and more extensive distribution.

Relation of Growth and Development to Temperature Regulation in Nestling Field and Chipping Sparrows

IT HAS long been known that the young of altricial birds make a striking transition from an essentially poikilothermic condition to a state of homeothermy during the nestling period. However, few detailed analyses have been made of the establishment of thermoregulatory capacity and of its relation to the general pattern of growth and development. This paper reports a study of nestlings of the eastern field sparrow, Spizella pusilla pusilla, and the eastern chipping sparrow, S. passerina passerina, based on observations of development under natural conditions and on laboratory investigations of the effects of environmental temperature on metabolism and body temperature. These species were chosen for study for several reasons: (1) both have a very short nestling period and correspondingly rapid development; (2) both occur in the same habitat in the area studied and are there subjected to the same general climatic conditions, thus affording an excellent opportunity for physiological comparison of closely related sympatric forms; and (3) both have been the subjects of intensive population studies by the junior author since 1949.