Responses to Temperature by the Spotted Nightjar (Eurostopodus Guttatus)

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RESPONSES TO TEMPERATURE BY THE SPOTTED NIGHTJAR (EUROSTOPODUS GUTTATUS)

WILLIAM R. DAWSON AND CHARLES D. FISHER Department of Zoology The University of Michigan Ann Arbor, Michigan 48104

Caprimulgid birds have proved to be intrigu- Western Australia, Nedlands, for study. A scarcity ing subjects for physiological research. Some, of moths in the vicinity forced considerable experi- mentation to establish a satisfactory diet. This consisted the Poor-will ( Phulaenoptilus nuttallii the ), principally of cockroaches and a vitamin mix- Common Nighthawk (Chordeiles minor), and ture, which were ultimately supplemented by grass- the European Nightjar (Caprimulgus euro- hoppers and an occasional moth. These items were paeus), have been observed to become dor- administered by hand nightly in sufficient quantity mant under appropriate conditions in the field so that the female had actually gained a couple of grams by the end of the three-week period of study. or laboratory (Jaeger 1948, 1949, 1954; Thor- The situation regarding the male is outlined sub- burg 1953; Marshall 1955; Novrup 1956; Bar- sequently in connection with observations on torpidity. tholomew et al. 1957; Howell and Bartholomew Oxygen consumption and evaporative water loss 1959; Bartholomew et al. 1962; Lasiewski and were measured simultaneously while the birds were resting in a postabsorptive state during the day, the Dawson 1964; Peiponen 1965, 1966). Several, normal period of quiesence in these nocturnal animals. the Poor-will, Common Nighthawk, and An open-circuit metabolism system was used in which Lesser Nighthawk ( Chordeiles acutipennis), air passed successively via tygon tubing through a have been found to excel in their resistance to drying train of silica gel and then Drierite ( anhydrous CaSOd), a suitably calibrated rotameter, and a cham- heat (Cowles and Dawson 1951; Bartholomew ber fashioned from a new 2-gal paint can. The tem- et al. 1962; Lasiewski and Dawson 1964; perature in this chamber, at the level of the bird, Lasiewski and Bartholomew lQ66). Acquisi- was measured with a thermocouple used in conjunc- tion of two Spotted Nightjars (Eurostopodus tion with a recently calibrated Brown recording potentiometer. The bird rested in the chamber on a guttutus) has afforded us the opportunity for wire mesh platform over a 1.5-cm layer of mineral oil examining the physiological responses to tem- which served to cover any droppings voided during perature of an additional caprimulgid. Some an experiment, thus preventing them from adding of our observations pertain to hotter condi- water vapor to the system. Evaporative water loss was determined by connecting two or (at high tem- tions than those utilized in previously pub- peratures) three tubes containing Drierite in series lished studies. The additional perspective our with the outflow line from the chamber. The gain data provide concerning thermoregulatory in weight of these tubes over a precisely timed interval capacities in the family and the fact that was determined with a Mettler balance of appropriate circumstances will prevent us from obtaining sensitivity. This gain, when reduced by a small correction value determined in a blank run preceding any more Spotted Nightjars in the foreseeable the experiment, represented the water evaporated by future prompt us to present our results in this the bird. The Drierite in the tubes recovered all but report. We acknowledge that a larger sample a small fraction of one per cent of known amounts of these birds would have been desirable. of water vapor introduced into the metabolism system with rates of air flow corresponding to those used in the experiments. These rates ranged from approxi- MATERIAL AND METHODS mately 700 to 2600 cm/min’ (ambient conditions) and were held constant in the individual experiments The Spotted Nightjar is resident over most of at levels that maintained the humidity within the Australia, except for the mesic parts of the east chamber near the following average values: 20”- coast, southeast, and southwest. It is also reputed 3O”C, 19 per cent (relative humidity) and 5 mm to occur on the Aru Islands and New Ireland (see Hg (vapor pressure of water); 30”-4O”C, 20 per cent Cayley et al. 1959), but this has been questioned and 8 mm Hg; 40”-45”C, 16 per cent and 10 mm by Peters ( 1940:190). The male and female used Hg; 45”-5O”C, 16 per cent and 13 mm Hg; 52.8”C, in this study were obtained on 30 December 1967 18 per cent and 17 mm Hg; 56.5”C, 20 per cent and from a mist net that had been left standing overnight 25 mm Hg. These values were determined using the near a water hole at Thundelarra Station (approxi- equation employed by Lasiewski (1964) and stan- mately midway between Yalgoo and Paynes’ Find), dard physical tables. Western Australia. This area is in the mulga (prin- Measurement of oxygen consumption required di- cipally Acacia aneura) belt. The Spotted Nightjar also occurs in mallee and in desert scrub. The two verting a portion of the air stream passing from the birds weighed between 85 and 90 g at capture and drying tubes through a train containing Ascarite (a were undoubtedly adjusted to the hot conditions of CO2 absorbent) and Drierite to a Beckman para- the austral summer. They were transferred within a magnetic oxygen analyzer of appropriate sensitivity. week to the Department of Zoology, University of The oxygen consumption was determined from the r491 The Condor, 71:49-53, 1969 50 WILLIAM R. DAWSON AND CHARLES D. FISHER

tively, amount to 49 and 79 per cent of the values characterizing most other nonpasserine 2.5 - birds of comparable size. The metabolic pat- Spotted Niqhtjor tern of the Spotted Nightjar resembles the 2.0 - . L . patterns for these other two species in another . l h important respect-oxygen consumption and 2.5-’ l . hence heat production increases relatively . F‘ . . little at high temperatures. It reached only “6 1.0 - l . 0 l : 1.4 times the basal rate at 52.8%. Much of 0.5 - . this rise is probably associated with the moderately increased body temperatures noted 0 I 20 30 40 50 60 at high ambient temperatures (see fig. 4). OC The relatively low energy requirement of evaporative cooling reflects the use of gular FIGURE 1. Rates of oxygen consumption by Spotted fluttering by the nightjar. The nature and Nightjars resting and fasting at various ambient temperatures. The value of 0.4 cm ’ 02 (g x hr)-1 ob- significance of this mechanism have most re- served at 23.7% pertains to a torpid individual with cently been reviewed by Lasiewski and Bar- a body temperature of 296°C (see text). tholomew ( 1966) and Bartholomew et al. ( 1968). We lacked equipment to determine flow rate registered by the rotameter and from the the flutter frequency employed by the night- difference in the fractional concentrations of oxygen jar, but it appeared to be in the same range between this air samnle and nure air (both dried and COpfree). The applicable equation from Depocas (approximately 600 cycles per minute) as that and Hart ( 1957) was used. All gas volumes ex- characterizing the Poor-will and Common pressed in connection with metabolic rate have been Nighthawk (see Lasiewski and Bartholomew corrected to 0°C and 760 mm Hg. 1966). Only at 56.5”C, an ambient tempera- Experiments typically lasted four or five hours ture that produced fatal overheating of the with determinations of oxygen consumption and evaporative water loss being made during the last female nightjar after 100 min, did the meta- hour. At that time the bird had fasted approximately bolic rate become conspicuously elevated with 16 hours. Below 42°C the temperature in the chamber exposure to heat. This development is best was held constant throughout the experiment. For considered in relation to the fact that the studies at higher temperatures a modified procedure was used to prevent excessive water loss over the drying power of air is determined both by its four- to five-hour period. The bird was allowed an water content at inspiration and its tempera- hour or so to adjust to the chamber while it was at ture at expiration. In the experiment at a moderate temperature. The chamber was then 56.5”C, the vapor pressure of water in the brought to the desired high temperature over the next hour. A measurement period lasting 15 to 30 inspired air approximated 25 mm Hg. Prior min was begun when the bird had been at the to heat injury, this air was probably expired desired ambient temperature for 1% to 2 hr. Above by the nightjar at a temperature somewhere 50°C a I5-min measurement starting at the end of near 42°C; Lasiewski and Bartholomew (1966) the first hour was also made. Body temperature was found mucosal temperatures in the gular area measured at the end of each experiment using a thermometer designed for small-animal work. The to fall between 39” and 40°C in a Poor-will nightjars proved exceedingly tractable experimental studied at ambient temperatures of 44”- subjects. 47.5%. At 42°C the effective saturation deficit of the air inspired by the nightjar RESULTS AND DISCUSSION would approximate only 37 mm Hg, cor- The rates of oxygen consumption by the responding to 40 per cent relative humidity. nightjars at various ambient temperatures are It is therefore not surprising that the nightjar illustrated in figure 1. The basal level of was forced to expend far more vigorous efforts metabolism is estimated to be 0.83 cm3 02 in evaporative cooling at 56.5% than at some- (g x hr)-l. This is 63 per cent of the value what cooler ambient temperatures where both predicted for an 88-g bird using Lasiewski the thermal differential between body and air and Dawsons’ (1967) equation relating basal and the absolute humidity were less. metabolic rate and body weight in nonpas- Heat production in the nightjar begins to serine birds. This relatively low level of metabolism is consistent with the situation rise as ambient temperature falls below ap- noted in the two caprimulgid birds on which proximately 32°C. The onset of chemical detailed observations have been made (Bar- thermoregulation, i.e., regulation primarily by tholomew et al. 1962; Lasiewski and Dawson adjustment of heat production, at this rela- 1964). The basal rates of the Poor-will (40 tively high temperature level is associated g) and Common Nighthawk (75 g), respec- with the relatively low level of basal metab-

52 WILLIAM R. DAWSON AND CHARLES D. FISHER

30 Spotted nightjar 50 . -3 t Spotted nightjar 0” .

3 20 - .

. . . T, (“C 1 0 .f . . , 20 30 40 50 60 FIGURE 4. Body temperatures of euthermic Spotted OC Nightjars resting and fasting at various ambient temperatures. TB = Ta along diagonal line. FIGURE 3. Evaporative water loss (data from fig. 2) per unit of oxygen consumption (data from fig. 1) in euthermic Spotted Nightjars. Conversion of data and the fairly effortless character of the gular on these functions to caloric terms (1 mg Ha0 = 0.57 flutter of this species contribute to this capac- Cal; 1 cm ’ 0~ = 4.7 Cal) permits expression of evaporative cooling (E) per unit of heat production (P) ity. on the right ordinate. The availability of simultaneous measure- ments of oxygen consumption (fig. 1) and water loss (fig. 2) permit calculation of values olism exceeds 1 mg/cm” O2 at all temperatures for the thermal conductance of the nightjar, studied (fig. 3). The values obtained are in corrected for evaporative cooling. These are general agreement with those reported for expressed in surface-relative terms in table 1, corresponding temperatures in the Poor-will body surface being calculated from the equa- and Common Nighthawk (Bartholomew et al. tion S = 0.1W”.67, where S is surface in m2 and 1962; Lasiewski and Dawson 1964), but dif- W is weight in kg. Thermal conductance pro- ferences in humidity among the three sets of vides an index of insulation (insulation = experiments hinder detailed comparisons. Ox- conductance-l) at the various ambient tem- idative water production is inadequate to off- peratures studied. The minimum conductance set evaporative water loss at moderate tem- value obtained for the nightjar, 1.7 kcal m-2 peratures in all three species and the situation hrlC1,’ is similar to that estimated for the is even less favorable at higher temperatures. Poor-will (40 g ), rather than that ( approxi- The insectivorous habits of these birds must mately 2 kcal m-2hr10C-1) for the Common contribute to rectification of this situation by Nighthawk, a caprimulgid more nearly its making available relatively large amounts of size. The maximal value (4.9 kcal m-2hr-10C-1 ) preformed water. The Spotted Nightjar also obtained for the nightjar exceeds the minimal appears to drink on the wing at water holes value by a factor of 2.9. The comparable ( Fisher, unpublished data). factor for the Roadrunner (Geococcyr cali- Water loss through evaporation and oxygen fornianus), a 285-g bird occupying regions consumption can both be converted to calories with temperature regimes approximating those (we have used 0.57 cal/mg of Hz0 and 4.7 for the area in which the Spotted Nightjar Cal/cm” 02 ) . Consequently, it is possible to evaluate the evaporative cooling of the Spotted Nightjar in relation to metabolism, TABLE 1. Thermal conductance* of the Spotted Nightjar at various ambient temperatures. as indicated on the right-hand ordinate of figure 3. This bird can dissipate slightly more TbeIlWd Ambient temp. conductance than three times its heat production at high “C (kcal m-2 lx- ’ “CY) ambient temperatures. This is a larger factor than those obtained in published studies of 23.023.5 1.71.9 the Poor-will and Common Nighthawk (Bar- tholomew et al. 1962; Lasiewski and Dawson 24.727.4 2.23.3 1964), but these other birds were studied at 28.128.3 3.31.6 lower temperatures and different humidities. The fact that the nightjar can dissipate signifi- 40.143.3 4.02.8 cantly more heat than it produces allows it to 48.6 remain substantially cooler than its surround- 52.8 ings at very high ambient temperatures (fig. heat produced -heat evaporated 8 Thermal conductance = 4). The relatively low level of metabolism (body temp. - ambient temp. ) (m*) THERMAL RESPONSES IN EUROSTOPODUS 53 occurs, is about 2.7 (Calder and Schmidt- sumption, evaporative water loss, and heart rate Nielsen 1967). in the Poor-will. Condor 64:117-125. BARTHOLOMEW, G. A., R. C. LASIEWSKI, AND E. J. It is of interest that the thermal conduct- CRAWFORD. 1968. Patterns of panting and ance of the nightjar reached its highest level gular flutter in cormorants, pelicans, owls, and at ambient temperatures exceeding body tem- doves. Condor 70:31-34. perature. Increasing conductance would be CALDEFI, W. A., AND K. SCHMIDT-NIELSEN. 1967. Temperature regulation and evaporation in the advantageous as ambient temperature rises pigeon and the Roadrunner. Amer. J. Physiol. to near body temperature, assuming that the 213:883-889. animal is not exposed to intense solar radia- CAYLEY, N. W., A. H. CHISHOLM, K. A. HINDWOOD, tion. However, a continued increase as am- AND A. R. MCGILL. 1959. What bird is that? bient temperature exceeds body temperature Third ed. Angus and Robertson, Sydney. COWLES, R. B., AND W. R. DAWSON. 1951. A would appear deleterious, since it would fa- cooling mechanism of the Texas Nighthawk. cilitate gain of heat from the environment. Condor 53 : 19-22. The possibility exists that the rise in conduct- CRAWFORD, E. J., JR., AND R. C. LASIEWSKI. 1968. ance is associated with the increased rates of Oxygen consumption and respiratory evaporation of the Emu and Rhea. Condor 70:333-339. air flow employed at high ambient tempera- DEPOCAS, F., AND J. S. HART. 1957. Use of the tures. However, the velocity of the air within Pauling oxygen analyzer for measurement of the chambers even at a flow rate of 2600 cm”/ oxygen consumption of animals in open-circuit min should be less than 10 cm/min, with the systems and in a short-lag, closed-circuit ap- oaratus. T. AUDI. Phvsiol. 10:388392. cross sectional area of the 2-gal paint cans HOWELL, T. R., i& G. .A. BARTHOLOMEW. 1959. used. Perhaps the relatively high conductance Further experiments on torpidity in the Poor- (and, therefore, low insulation) noted at 48.6” will. Condor 61: 180-185. and 52.4% results from the movements and JAEGER, E. C. 1948. Does the Poor-will “hiber- postural adjustments associated with rapid nate”? Condor 50:45-46. JAEGER, E. C. 1949. Further observations on the evaporative cooling. hibernation of the Poor-will. Condor 51: 105-109. SUMMARY JAEGER, E. C. 1954. Bird that “sleeps” all winter. Desert Mag. 17:21-22. The Spotted Nightjar is a bird with superior LASIEWSKI, R. C. 1964. Body temperatures, heart powers of heat defense which depend princi- and breathing rate, and evaporative water loss in pally on an extensive capacity for evaporative hummingbirds. Physiol. Zool. 37:212-223. LASIEWSKI, R. C., A. L. ACOSTA, AND M. H. BERN- cooling via gular fluttering and a relatively STEIN. 1966. Evaporative water loss in birds- low level of metabolism. Body temperature II. A modified method for determination by tends to be rather labile at moderate ambient direct weighing. Comp. Biochem. Physiol. 19: temperatures and a capacity for dormancy is 459-470. indicated, although it remains to be established LASIEWSKI, R. C., AND G. A. BARTHOLOMEW. 1966. Evaporative cooling in the Poor-will and Tawny whether or not nightjars become torpid in Frogmouth. Condor 68:25%262. nature. The Spotted Nightjar resembles the LASIEWSIU, R. C., AND W. R. DAWSON. 1964. somewhat smaller Poor-will in those aspects Physiological responses to temperature in the of its physiology that have been investigated. Common Nighthawk. Condor 66:477-490. LASIEWSKI, R. C, AND W. R. DAWSON. 1967. A This is consistent with the ecological similar- re-examination of the relation between standard ities between the two birds. metabolic rate and body weight in birds. Condor 69: 13-23. ACKNOWLEDGMENTS LASIEWSIU, R. C., AND R. J. LASII+~SKI. 1967. This study was supported in part by a grant Physiological responses of the Blue-throated and from the National Science Foundation (GB- Rivolis’ Hummingbirds. Auk 8433448. 3656). Professor H. Waring graciously ex- MARSHALL, J. T., JR. 1955. Hibernation in captive tended us many courtesies and use of lab- goatsuckers. Condor 57: 129-134. NOVRUP, L. 1956. Natravn (Cuptim&us euro- oratory facilities within the Department of paeus L.) fundet i dvaletihtand. Dansk Ornithol. Zoology, the University of Western Australia, Foren. Tids. 50:77-79. for which we are very grateful. We should PEIPONEN, V. A. 1965. On hypothermia and also like to acknowledge the cooperation and torpidity in the nightjar (Caprimulgus europaeus L.). Ann. Acad. Sci. Fennicae A. IV. 87: assistance of Professor A. R. Main of that 15 PP. Department. PEIPONEN, V. A. 1966. The diurnal heterothermy LITERATURE CITED of the nightjar (Cuprimulgus europaeus L. ). Ann. Acad. Sci. Fennicae A. IV. 101:35 pp. BARTHOLOMEW, G. A., T. R. HOWELL, AND T. J. PETERS, J. L. 1940. Check-list of birds of the world. CADE. 1957. Torpidity in the White-throated Vol. IV. Harvard Univ. Press, Cambridge. Swift, Anna Hummingbird, and Poor-will. Condor THORBURG, F. 1953. Another hibernating Poor- 59 : 145-155. will. Condor 55:274. BARTHOLOMEW, G. A., J. W. HUDSON, AND T. R. HOWELL. 1962. Body temperature, oxygen con- Accepted for publication 9 April 1968.