Effects of Starvation on Wild Mallards

Abstract

Effects of deliberate starvation were studied in a total of 30 wild Anas platyrhynchos held in captivity in outdoor pens. Wt. losses in hens appeared to rise and fall alternately beginning with the 1st week and ending with the 4th week. The pattern was similar for drakes except that the wt. loss of the 3d week continued into the 4th week. Critical body wts. were reached during the 3d and 4th weeks, and the frequency of mortalities was greatest during the 4th week. Red blood cell counts and hemoglobin content of blood were less reliable than body wt. as an indicator of the severity of starvation. Air temp. influenced the extent of wt. losses. In drakes, that succumbed, the loss of initial wt. was greatest in summer, less in spring, and least in winter. The mortality rate in drakes was double that for hens during the spring breeding season. This may be related to a differential ability of the sexes at this season to store fat which provides more energy per unit of wt. than protein does; it may also be related to different rates of metabolism during the stresses of starvation. Examination of tissues of starved birds showed that the kidneys were most resistent to atrophy. The wt. lost by the liver was proportionately greater than the body wt. loss, and that lost by the heart proportionately less. When supplied with food, both sexes of ducks recovered from losses of initial body wt. averaging about 44%. No objective symptoms of previous functional damage to tissues were observed in birds that recovered from acute starvation.