title: Hummingbirds arrest their kidneys at night: diel variation in glomerular filtration rate in Selasphorus platycercus.
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.
authors.affiliation: Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: Bradley Hartman
authors.initials: BH
authors.lastname: Bakken
authors.forename: Todd J
authors.initials: TJ
authors.lastname: McWhorter
authors.forename: Ella
authors.initials: E
authors.lastname: Tsahar
authors.forename: Carlos Martínez
authors.initials: CM
authors.lastname: Del Rio
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001717:Birds / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D005247:Feeding Behavior / Q000502:physiology; D005919:Glomerular Filtration Rate / Q000502:physiology*; D007668:Kidney / Q000502:physiology*; D008954:Models, Biological; D010802:Phylogeny; D014867:Water / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D014867:Water