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Comparative Study
. 2004 Dec;207(Pt 25):4383-91.
doi: 10.1242/jeb.01238.

Hummingbirds Arrest Their Kidneys at Night: Diel Variation in Glomerular Filtration Rate in Selasphorus Platycercus

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Comparative Study

Hummingbirds Arrest Their Kidneys at Night: Diel Variation in Glomerular Filtration Rate in Selasphorus Platycercus

Bradley Hartman Bakken et al. J Exp Biol. .
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Abstract

Small nectarivorous vertebrates face a quandary. When feeding, they must eliminate prodigious quantities of water; however, when they are not feeding, they are susceptible to dehydration. We examined the role of the kidney in the resolution of this osmoregulatory dilemma. Broad-tailed hummingbirds (Selasphorus platycercus) displayed diurnal variation in glomerular filtration rate (GFR). During the morning, midday and evening, GFRs were 0.9+/-0.6, 1.8+/-0.4 and 2.3+/-0.5 ml h(-1), respectively. At midday, GFR increased linearly with increased water intake. During the evening, hummingbirds decreased renal fractional water reabsorption linearly with increased water intake. Broad-tailed hummingbirds appeared to cease GFR at night (-0.1+/-0.2 ml h(-1)) and decreased GFR in response to short-term ( approximately 1.5 h) water deprivation. GFR seems to be very responsive to water deprivation in hummingbirds. Although hummingbirds and other nectarivorous birds can consume astounding amounts of water, a phylogenetically explicit allometric analysis revealed that their diurnal GFRs are not different from the expectation based on body mass.

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