Date of Award:

5-1-1985

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

James A. Gessaman

Committee

James A. Gessaman

Committee

Keith Dixon

Committee

LeGrande Ellis

Committee

Barrie Gilbert

Committee

Ivan Palmblad

Abstract

The six major components of the water economy of nestling Swainson's Hawks (Buteo swainsoni) were quantified and incorporated into water budget scenarios demonstrating the effects of heat stress and dietary composition on water balance. Four consecutive 1-week food trials were conducted on each of 16 nestlings to measure rates of food consumption, growth, energy utilization, excrement production and pellet production. Rates of evaporative water loss and CO2 production were measured gravimetrically on 28 nestlings under 4 thermal conditions (25°C, 35°C, 42°C, and 30°C plus sunlight) using an open flow indirect calorimetry system. Water utilization components ( i.e., water storage in body tissue and water loss in excrement and pellets) increase to a peak when nestlings are about 3 weeks old, an age when their growth rates and food consumption are near maximal levels. Rates of preformed water consumption reach peak levels during the fourth week after hatch, when large, rapidly growing nestlings consume food at maximum rates. Metabolic water constitutes 10-19% of the total water input and is generated by nestling metabolic rates considerably higher than predicted from an allometric equation for adult falconiform birds. Basal rates of evaporative water loss of nestlings (at 25°C) are significantly higher than rates predicted from an allometric equation for adult birds of other species. Maximal rates of evaporative water loss of nestlings (at 42°C) are 3-8 times their basal rates (at 25°C), but are only 79-84% of the maximal rates predicted from an allometric equation for adult birds of other species. The inverse relationship between body fat content (or energy density) and body water content in small mammalian prey has: 1) a dramatic effect on the magnitude of preformed water consumption, 2) a lesser effect on excretory water loss, and 3) a negligible effect on metabolic water production. The consequences of these relationships is that body composition of the prey has an overriding influence on the status of nestling water balance. Low fat diets should supply nestlings with a surplus of water, whereas high fat diets would not provide enough water to meet even the minimum water needs of non-heat stressed nestlings.

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