The Ruby-throated Hummingbird and its major food plants: ranges, flowering phenology, and migration

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Abstract
The ruby-throated hummingbird (or rubythroat, A. colubris) and several of its major food plants were examined to assess the importance of rubythroat vs. insect pollination, the overlap of geographical ranges and the synchrony between migration and flowering times. Seed set of Impatiens biflora was increased 8-17% by rubythroat and insect visitation over the level achieved by insects alone. The rubythroat''s range is not contiguous with that of any of 22 putative food plants examined, but is nearly coincident with the range of certain forest types, perhaps reflecting the importance of sap for food. A new method was developed to estimate peak flowing times of plants from herbarium data. Based on these data and field observations, only 1 rubythroat food plant (I. biflora) had peak flowering times close to peak rubythroat migration times throughout their shared range. Rubythroats and their North American food plants are facultative mutualists, with the plants apparently having been evolutionarily more labile.