Respiratory metabolism studies on red-winged blackbird nestlings

Abstract

Nestling red-winged blackbirds exhibited two distinct metabolic reactions to lowering temperatures. One group, which maintained homeothermic conditions, elevated its metabolism linearly according to a drop in ambient temperature and the second decreased its metabolic response in a curvilinear fashion. Core temperatures showed that although there was a progression toward the establishment of homeothermy throughout the nestling period, the birds could and did drop their core temperatures when the temperature gradient was too great to maintain constant body temperature. In some instances it is felt that oxygen consumption, and thus metabolism, was lowered before body temperature was suddenly dropped. No differences in the rates of metabolism could be found between upland and marshland populations; however, differences between values of the respiratory quotient for the two populations were found (p < 0.001). In addition differences in R.Q. values were found between well-developed nestlings practicing homeothermy and those that became hypothermic in response to lowering environmental temperature.

Thermoregulatory strategies of songbird nestlings reveal limited capacity for cooling and high risk of dehydration

“…A number of studies measured metabolic rate (O2 consumption or CO2 production) of nestlings over a range of temperatures to investigate the development of endothermy. From the figures presented in those studies, the lower critical limit of the thermoneutral zone seems to typically fall between 30-35°C (Dawson & Evans, 1957, 1960Dyer, 1968;Mayer et al, 1982;Nager & Wiersma, 1996;Sirsat et al, 2016), which is consistent with the lower critical limit we identified for superb fairy-wren nestlings. Only one study of developing cattle egret (Bubulcus ibis) nestlings studied higher temperatures (up to 45°C) (Hudson et al 1974), which suggested metabolic rate to be minimal from 34°C to 40°C, relatively similar to superb fairy-wren nestlings despite the difference in the body size and ecology of the species.…”

Thermoregulatory strategies of songbird nestlings reveal limited capacity for cooling and high risk of dehydration

“…A number of studies measured metabolic rate (O2 consumption or CO2 production) of nestlings over a range of temperatures to investigate the development of endothermy. From the figures presented in those studies, the lower critical limit of the thermoneutral zone seems to typically fall between 30-35°C (Dawson & Evans, 1957, 1960Dyer, 1968;Mayer et al, 1982;Nager & Wiersma, 1996;Sirsat et al, 2016), which is consistent with the lower critical limit we identified for superb fairy-wren nestlings. Only one study of developing cattle egret (Bubulcus ibis) nestlings studied higher temperatures (up to 45°C) (Hudson et al 1974), which suggested metabolic rate to be minimal from 34°C to 40°C, relatively similar to superb fairy-wren nestlings despite the difference in the body size and ecology of the species.…”

Energetic Consequences of Sexual Size Dimorphism in Nestling Red‐Winged Blackbirds

“…For males the total budget is composed of 19% growth and 81% maintenance energy, for females 17% growth and 83% maintenance (Table 3). Dyer (1968) found SMR's of 0 2 consumption by nestling Red-winged Blackbirds ranging from 2.80 to 3.20 mL·g-1 ·h-1 , and Brenner (1968) reported dayand nighttime "mean metabolic rates" of 0 2 consumption by nestlings of 2.91 and 1.65 mL·g-1 ·h-', respectively. Our FMR estimates are more than twice these values.…”

“…We presume that nocturnal expenditures on activity are minimal, and one would expect the FMR to approach the SMR. If the nestlings were exposed to an effective night temperature of 20°C, the excess over the thermoneutral SMR could be fully accounted for as expenditure on thermoregulation (Dyer 1968). This is plausible; the mean minimum air temperature during the isotope-sampling days was 11°C.…”