Fig. 4. Glomerular filtration rates (GFR) in broad-tailed hummingbirds before, during and after a 1.5 h food/water deprivation episode. During food/water removal, mean GFR was significantly reduced relative to the pre-removal period (GFR'_FAST and GFR_MIDDAY were equal to 0.9±0.5 and 1.8±0.4 ml h^–1, respectively; N=9). When we returned the food/water, GFR_RETURNED (1.4±1.0 ml h^–1; N=9) was not different from either GFR_MIDDAY or GFR'_FAST. GFR_PREDICTED is equal to 2.1 ml h^–1 (Bennett and Hughes, 2003).