Nicotiana attenuata, an herbaceous annual plant of disturbed sites in cold deserts of western North America, has traits that suggest adaptations for hawkmoth (Sphingidae, e.g., Hyles lineata or Manduca spp.) pollination. The tubular flowers are white and open fully at night and twilight, often closed by midday. Nectar is produced between dusk and dawn, and if not harvested is reabsorbed between dawn and midday. At our study site in northern Arizona, hawkmoths were absent or scarce during September and early October 1994, but migrating female and juvenile Selasphorus hummingbirds (rufous and broad-tailed hummingbirds) visited flowers regularly during morning or evening and briefly defended territories centered on plants. Most of these hummingbirds disappeared from the patch at midday. We found only weak evidence that hummingbirds have acted as agents of selection on floral traits of N. attenuata. Nectar production was low (ca. 1.15µl/flower/night, containing 0.43 mg sugar) relative to most hummingbird flowers of the western United States, and although hummingbirds obtained a short-term profit from N. attenuata in the morning and early evening when nectar standing crop was high, most birds could not meet their daily energy requirements by foraging exclusively on its flowers. Hummingbird pollination has no impact on female fitness of N. attenuata, because seed production was not affected by provision of self or outcross pollen. Our results demonstrate the opportunism of migrant hummingbirds and suggests the potential for evolution of floral traits to proceed from such an opportunistic use of a plant in the absence of its syndrome pollinator.