BARBOZA, P.S.; JORDE, D.G.: Male and female black ducks respond differently to intermittent feeding in winter

Feeding is limited by predation and weather during winter, migration and breeding of black ducks (Anas rubripes). Restricted food intake can affect body composition, molt and egg production of waterfowl. We studied responses of captive birds to restricted feeding time without limiting abundance or changing quality of food during winter (January – March) and spring (April – May). A complete diet was provided ad libitum on consecutive days each week: 7d (9 male:9 female), 5d (9:9), or 3d (11:12). Weekly food intakes of males were similar among treatments but fasted females consumed more than unfasted females in January. Daily food intake of fasted birds were increased by 2.35 and 3.97 times that of unfasted males and females respectively. Although both sexes lost body mass, fasted females lost less mass and lipid than unfasted females during winter. Body N was conserved in both sexes even though heart and spleen lost mass whereas mass of kidney, reproductive tract and liver increased over winter. Intermittent feeding increased liver, intestine and digesta masses of females but did not affect nutritional organs of males. Intermittent feeding delayed egg production in spring but did not affect clutch size, egg fertility or hatching. Females fasted for 4d/wk were still heavier than controls after laying eggs. Black ducks combine ingestive flexibility with plasticity of the digestive tract, liver and adipose to contend with a variable food supply during winter. Intermittent feeding delays reproduction in females even though they retain sufficient body mass to lay eggs. This suggests that female black ducks use supplemental cues from the environment to modulate endogenous reserves for survival and to defer reproductive commitment in spring.