The Water Economy of the Black-Throated Sparrow and the Rock Wren

Abstract

Black-throated sparrows do not need to drink when they can eat green vegetation or insects, but in areas where water is available they drink regularly when they are mainly eating seeds. Rock wrens do not need to drink but obtain water from the insects they eat. On a dry diet in the laboratory black-throated sparrows drank 30% of their body weight per day when given water ad libitum, but most individuals survived indefinitely without drinking. When deprived of water, they did not reduce their activity. Drinking of NaCl solutions decreased with increasing molarity. Birds maintained their body weight when drinking 0.4 [image],or less concentrated solutions of NaCl. Birds which drank 0.5 [image], or 0.6 [image] NaC1 lost weight. When given NaC1 by stomach tube, black-throated sparrows commonly produced urine with a Cl concentration of more than 5000 meq/liter, and 1 birdproduced urine with 703 meq/liter. When drinking water was withheld, the water content of the excreta of black-throated sparrows, which is normally about 81%, decreased to 57%. The maximum urinary chloride of rock wrens given NaCl by stomach tube varied from 325 to 403 meq/liter.