Robert C. Lasiewski

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

Evaporative water loss in birds—I. Characteristics of the open flow method of determination, and their relation to estimates of thermoregulatory ability

Abstract 1. 1. Virtually all of our knowledgeof avian evaporative water loss is based on open flow determinations, and several generalizations concerned with water loss are based on insufficient information because of limitations in this technique. 2. 2. Some characteristics of the open flow system as they relate to measurement of avian evaporative water loss are examined, and a new formula for predicting relative humidity in the respiratory chamber is presented and tested. 3. 3. Air flow rate (and the resultant humidity in the chamber) influences the effectiveness of evaporative cooling in open flow determinations. Higher air flow rates (lower humidities) permit many avain species to dissipate all of their metabolic heat through evaporative cooling. 4. 4. A wide variety of birds were capable of maintaining their body temperatures below environmental temperatures of 44°–46°C for periods ranging from 1 to 4 hr through evaporative cooling.

A preliminary allometric analysis of respiratory variables in resting birds

Abstract Preliminary allometric equations relating avian respiratory variables to body weight permit a series of tentative statements regarding avian respiration which were hitherto impossible. Comparisons of avian and mammalian equations reveal dimensional similarities and differences in the two distinct respiratory systems. The avian lung is similar in weight but has a proportionately smaller air space than its mammalian counterpart. The total volume of the avian respiratory system is much greater than that of mammals. Avian tidal volumes are larger than those of mammals, but avian respiratory rates are lower, and avian minute volumes are somewhat less than in comparable sized mammals. Each tidal volume in birds provides air equivalent to a complete turnover of the airspace of the lungs plus trachea. Avian respiration provides a more extensive CO 2 washout in the tertiary bronchi exchange areas than occurs in the mammalian alveoli. The amount of oxygen removed from respiratory air in birds is independent of body weight, as it is in mammals, and birds may remove a greater proportion of the oxygen than do mammals.

Heating and cooling rates, heart rate and simulated diving in the Galapagos marine iguana

Abstract 1. 1. During enforced submergences of 30–50 min, the animals remained quiet. Bradycardia developed slowly following submergence and conspicuous arrhythmia appeared. Bradycardia ended almost immediately following the termination of submergence. 2. 2. In both air and water the lizards heated approximately twice as rapidly as they cooled. 3. 3. Heart rate at any given body temperature was much slower during cooling than during heating, suggesting that circulatory adjustments are important in controlling rate of temperature change. 4. 4. Minimum heart rates in air increased with increasing temperature, and at all temperatures the smaller animal had a more rapid heart beat than the larger one. 5. 5. Ecological and comparative aspects of the responses of the marine iguana are discussed.

Physiological responses of the giant hummingbird, Patagona gigas

1. 1. Standard metabolic rate of three Giant Hummingbirds (mean weight, 19·1 g) was 2·7 cm3 O2/g/hr, and thermal conductance was 0·17 cm3 O2/g/hr/°C. 2. 2. Torpid metabolism increased exponentially with ambient temperature (Q10 = 3·7). 3. 3. Thermal conductance in birds is inversely related to body weight, described by: log C = log 0·848–0·508 log W, where C is thermal conductance in cm3 O2/g/hr/°C, and W is body weight in grams. 4. 4. Rates of entry into and arousal from torpor are inversely related to body weight. 5. 5. Evaporative water loss is inversely related to ambient water vapor pressure at ambient temperature of 25°C. 6. 6. Homeothermic heart rates ranged from 300–1020/min, and minimum breathing rate was 106/min. Wing beat frequency during hovering flight was 15/sec.

TEMPERATURE REGULATION AND RESPIRATION IN THE OSTRICH

The Ostrich (Struthio camelus), the largest living bird, is an inhabitant of semi-arid and desert areas of Africa and, until exterminated, the Near East and the Arabian Peninsula. When exposed to the heat stress of a hot desert, it must use water for evaporation in order to avoid overheating. While its size prevents it from taking advantage of microclimates to the extent that small desert birds and mammals can, its large size is an advantage in its water economy, as has been discussed previously (Schmidt-Nielsen 1964). Birds have no sweat glands, and under heat stress they rely upon increased evaporation from the respiratory system as a major avenue for heat dissipation. We were interested in the role of the respiratory system in evaporation, and particularly in the sites of evaporation. Furthermore, while in mammals an increased ventilation causes alkalosis, in birds the presence of large air sacs connected to the respiratory system may have radically different effects on the gas exchange in the lung. Finally, the fact that the ventilation of the respiratory system can be modified by heat stress without change in the rate of oxygen consumption may provide an avenue for investigation of the poorly understood air-sac system of birds. The Ostrich, although a non-flying bird, has a well developed air-sac system, and its large size and slow breathing rate provide an opportunity to undertake experimental procedures which in smaller birds result in great technical difficulties or seem impossible. MATERIALS AND METHODS

Oxygen Consumption and Respiratory Evaporation of the Emu and Rhea

with units as in equation 3. Although the data in equation (4) represent 58 species, only the Ostrich and Cassowary weighed more than 10 kg. Equation (4) is statistically indistinguishable from a comparable equation presented by King and Farner (1961) for birds weighing 0.125-10.0 kg. The relation between avian evaporative water loss and body weight conforms to a pattern similar to that for metabolism and body weight. Bartholomew and Dawson (1953) presented data for avian species ranging from 10.8 to 147 g, showing that evaporative water loss per unit weight is inversely related to body weight. Crawford (1965) proposed a tentative equation relating these variables in birds:

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.

Patterns of Panting and Gular Flutter in Cormorants, Pelicans, Owls, and Doves

Most birds pant when subjected to heat stress, but some supplement evaporation from the respiratory tract by fluttering the gular area. Gular flutter occurs in at least the following taxa: cormorants, pelicans, boobies, anhingas, frigate-birds, herons, owls, doves, roadrunners, colies, and many gallinaceous species. The mechanics of gular flutter have been examined only in the Poor-will, Phalaenoptilus nuttallii (Lasiewski and Bartholomew 1966), but data on rates of gular flutter are available for a number of species, including the Common Nighthawk, Chordeiles minor (Lasiewski and Dawson 1964), Domestic Pigeon (Columba livia (Calder and Schmidt-Nielsen 1966), Bobwhite (Colinus virginianus), Gambels and California Quail (Lophortyx gambelii and L. californicus), Painted Quail, Excalfactoria chinensis, Screech Owl, Otus asio, and Mourning Dove, Zenaidura macroura (Lasiewski et al. 1966b). The ability of birds that employ gular flutter to dissipate all of their metabolic heat through evaporation has been demonstrated in the Poor-will (Bartholomew et al. 1962), Common Nighthawk (Lasiewski and Dawson 1964), Domestic Pigeon (Calder and Schmidt-Nielsen 1966), Inca Dove, Scardafella inca (MacMillen and Trost 1967), and the Painted Quail (Lasiewski et al. 1966a). In caprimulgids the rate of flutter is independent of heat load and appears to be determined by the resonant properties of the gular area, just as the panting rate of dogs is determined by the resonant properties of the thoraco-abdominal region (Crawford 1962). The present study was undertaken to examine aspects of gular flutter and breathing in several birds of widely differing morphology and behavior. Through the cooperation of the staff of the San Diego Zoological Gardens, we were able to make measurements on a Double-crested Cormorant (Phalacrocorax auritus), a Brown Pelican (Pelecanus occidentalis), a Homed Owl (Bubo virginianus), and a Barn Owl (Tyto alba). Mourning doves (Zenaidura macroura) and a Horned Owl were studied on the Los Angeles Campus of the University of California.

Roadrunners: Energy Conservation by Hypothermia and Absorption of Sunlight

Roadrunners sunning in artificial sunlight consume oxygen at standard (basal) levels at ambient temperatures as low as 9.0�C. Energy savings of sunning roadrunners averaged 551 calories per hour. In the dark, birds may undergo hypothermia. Hypothermic roadrunners can elevate their body temperatures to normal levels by sunning, at reduced metabolic cost.