Diurnal Variation in Mass, Metabolic Rate, and Respiratory Quotient in Anna's and Costa's Hummingbirds

Abstract

To examine how hummingbirds that do not enter torpor at night store and utilize energy, open-circuit respirometry and a strain gauge were used to measure daily variation in 0 2 consumption (Vo2), C02 production, respiratory quotient (RQ), and body mass in Anna's hummingbird, Calypte anna, and Costa's hummingbird, Calypte costae. During the day, Vo2 was highly variable primarily because of dif ferences in activity among individuals. At night Vo2 varied little between individuals, but mean Vo2 was more than two times that predicted from body mass for resting, postabsorptive birds. F<f'r C. anna, mean 24-hr energy expenditure was similar to that of free-living birds. Diel mass.fluctuations were large, up to 16% in both species. However, much of the observed change in mass was probably due to factors other than changes in body fat content. The RQ was well above 1. 0 throughout the day, suggesting continuous deposition of fat, and RQs remained high at night (>0.85), indicating the use of carbohydrate as a metabolic substrate. Predicted crop volumes of the hummingbirds are sufficient to store the amount of feeder solution (0.25 g sucrose per ml) required to account/or the observed nighttime RQs. This suggests that hummingbirds in this study were using their crop as a supplemental "energy storage depot " at night.

Metabolic substrate use and the turnover of endogenous energy reserves in broad-tailed hummingbirds (Selasphorus platycercus)

“…These results support the notion that fed hummingbirds fuel their metabolism primarily with recently ingested sugars, whereas fasted hummingbirds use endogenous reserves (Suarez et al, 1990). Our results are consistent with measurements on Anna's (Calypte anna) and Costa's (Calypte costae) hummingbirds (Powers, 1991). During the day, when birds were feeding, Powers found that their RQ was approximately 1.0, which indicates that birds were oxidizing sugars; after an overnight fast, their RQ was close to 0.7, which indicates that birds were oxidizing lipids (Powers, 1991).…”

“…Historically, studies investigating metabolic substrate use have relied on the respiratory quotient (RQ=V CO 2 . V O 2 -1 ) to assess whether carbohydrates, lipids or proteins support respiration (Surarez et al, 1990;Powers, 1991). Advances in elemental stable isotope analysis now allow an alternative/complementary method to RQ to determine metabolic substrate use.…”

Effect of photoperiod on body weight gain, and daily energy intake and energy expenditure in Japanese quail (Coturnix c. Japonica)

“…In this way the birds managed to consume more food than would be expected on the basis of time reduction only, and were able to gain weight continuously after the initial drop in weight gain. They were, however, unable to increase their food intake to such an extent that they consumed the same amount or more as birds subjected to light periods of at least 12 h. Crop (and digestive tract) filling is a generally adopted feeding strategy by birds possess-ing a crop that enables them to tide over prolonged fasting periods [1,2,5,14,28,41]. The effect of photoperiod on food intake found here was opposite to the effect of photoperiod on food intake as found in pigeons that were gradually transferred from a 12-h to a 3-h light period with only ad lib food during the light period: food intake increased when the birds were gradually subjected to shorter light periods [2].…”

Modulation of ingested water absorption by Palestine sunbirds: evidence for adaptive regulation

“…We assumed that metabolic water production was due only to carbohydrate catabolism. Indeed, the respiratory quotient (RQ) of actively feeding sunbirds and hummingbirds indicates carbohydrate catabolism (RQ=1.0; C. Hambly, B. Pinshow, E. J. Harper and J. R. Speakman, unpublished data; Suarez et al, 1990;Powers, 1991). Birds in this study were in mass balance during all experimental trials, so we further assumed that the rate of carbohydrate catabolism was equal to the rate of sucrose assimilation.…”