Is respirometry a standardized technique? A review of measurement of avian resting metabolic rates

A plethora of studies have been conducted since the 1920s on avian thermoregulatory physiology variables as measured using respirometry. In particular, many of these studies have determined basal metabolic rate in a wide array of avian taxa. Start time of experiment, duration of experiment, length and number of measurements to determine the resting metabolic rate at a particular temperature (RMRTa) were reviewed in avian metabolic studies prior to 2011. Although respirometry is considered a standard technique, it was evident that in avian studies there is a continuum of duration time used for measurements with a number of studies (30%) using only 1–2 h data collection while at the other end of the continuum a number of studies (22%) have used 9–15 h data collection (and some longer). Many studies are unclear in how many hours were used (22%) to collect data. We found that most avian studies (94%) were on postabsorptive birds and most were during the birds' rest phase (69.5%). The majority (62.6%) of studies only measured metabolic rate at one temperature per trial, while others (19.2%) have measured RMRTa at various temperatures within a single trial period. Recently, several studies have shown that for diurnal birds measurements need to be conducted during the scotophase, for the duration of the night (>9 h; except at extreme temperatures where evaporative water loss is high and may result in mortalities), and at one experimental temperature per night if reliable and precise data are to be obtained. In addition, repeated measures need to be stable for at least an hour to be considered as RMRTa. Consequently, given the variance in methods used in prior avian metabolic studies cognizance of this is required when designing and implementing avian thermoregulatory physiological measurements using respirometry, particularly if data are later used for comparative allometric studies.

► Trends in measuring avian minimum metabolic rate were reviewed.
► Although respirometry is considered a standard technique, it was found it is not.
► There was a continuum of duration time used for measurements.
► 94% of studies were on postabsorptive birds and 69.5% in the rest phase.
► 62.6 % of studies measured metabolic rate at one temperature per trial.