Meeting Abstract

6.10  Jan. 4  Mechanisms of water balance in hummingbirds HARTMAN BAKKEN, Bradley*; SABAT, Pablo; University of Wyoming, Laramie, Wyoming, USA; Universidad de Chile, Santiago, Chile bradley@uwyo.edu

Hummingbirds face a curious osmoregulatory dilemma. To meet their high mass-specific energy demands, they regularly ingest multiples of their body mass per day in water; yet, with a high mass-specific rate of total evaporative water loss and no capacity to form hyperosmotic urine, they are prone to dehydrating quickly during fasts. How do hummingbirds resolve this quandary? To avoid overhydration, hummingbirds rely on two renal mechanisms. The most prevalent of which is to reduce water reabsorption, but the rate at which body water is filtered appears to be responsive to water loading as well. To lessen the likelihood of dehydrating during fasting periods, hummingbirds greatly reduce, and even cease, renal filtration. Although this water conserving strategy reduces body water losses in urine, total evaporative water loss rates in resting hummingbirds indicate they still dehydrate during natural, overnight fasts. We have identified the strategies hummingbirds use to resolve their osmoregulatory dilemma; however, it remains unclear how they tolerate both renal �failure� and potentially severe dehydration.