Using a new browse-monitoring technique, short-term changes in the winter foraging behaviour of yarded northern white-tailed deer (Odocoileus virginianus) were followed over 3 winters. Hypotheses about selective browsing, shifts in foraging strategy, food patch selection, diet quality, and foraging effort were derived from optimal foraging theory. Testing of associated predictions disclosed that deer expanded their diets over the course of the yarding season, showed shifts in proportional representation of browse species in their diet, and exhibited distinct but changing preferences for certain browse types. Partial preferences in diet choices occurred, but important diet items were used in nonrandom runs once adopted into the diet. Cornus stolonifera was the dominant browse species in the diet based on construction of a functional response curve, with the use of other species influenced by C. stolonifera depletion. Deer took a greater number of twigs from denser browse plots, and made more browsing visits to dense plots over the yarding season. Browsed plots tended to be higher in total twig availability and C. stolonifera availability than unbrowsed plots for the first half of the yarding season only. Diameter at point of browsing (DPB) values increased over the season for C. stolonifera and Salix. Results indicate that winter deer foraging is a dynamic process, with high diet selectivity at the beginning of the yarding season, and gradual diet generalization in the face of overall browse depletion.

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