Enthusiasm for optimal foraging theory in the 1970s and 1980s stimulated much work on foraging by bees and, to a lesser extent, hummingbirds. These animals were assumed to be energetically stressed because they were nectarivorous, small, and dependent on costly forms of flight. Researchers sought to explain foraging in terms of movement patterns that saved energy. For example, Pyke (1981) derived movement rules both within and between inflorescences. He compared observed directions and distances of movements following departure from a flower to optimal predictions, under the assumption that the animals should maximize their net rate of energy intake. Pyke (and many others) also assumed that animals would have imperfect knowledge about their environments, particularly with regard to predictions as to what and where to find food in the future. In addition to using statistical rules (Pyke 1984), such animals should always sample in order to track an ever-changing world. Despite the power and appeal of this viewpoint, we now see growing evidence that simple rules and patterns alone cannot explain foraging in hummingbirds. Here, we review how learning and memory influence hummingbird foraging and how memory might affect the ways in which hummingbirds pollinate plants.

Much of a hummingbird's diet is derived from the nectar of flowers that, in turn, rely on hummingbirds for pollination. These flowers frequently provide only a few mg of sugar daily (Kodric-Brown & Brown 1978). Hummingbirds therefore must visit many flowers on each feeding bout, transferring pollen among flowers in the process.