Fig. 2. Diel variation in glomerular filtration rate (GFR) in broad-tailed hummingbirds. Our GFR estimates for the evening, night and morning were 2.3±0.5, –0.1±0.2 and 0.9±0.6 ml h^–1 (N=9), respectively, and were significantly different from each other. GFR_MORNING was lower than GFR_EVENING by a factor of 2.6, and GFR'_NIGHT was not different from 0. GFR_EVENING was approximately 110% of the allometric prediction (GFR_PREDICTED=2.1 ml h^–1; Bennett and Hughes, 2003).