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Dryad

Ornithophily in the trumpet creeper: floral metric data from the Ozark Mountains

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Sep 09, 2024 version files 11.15 KB

Abstract

The diversification of hummingbirds (Trochilidae) has shaped the pollination strategies and floral trait evolution in at least 68 families of flowering plants in the Western Hemisphere. The trumpet creeper (Bignoniaceae) is the quintessential example of ornithophily in eastern North America. The mutualistic relationship between this flamboyantly-flowered liana and the ruby-throated hummingbird (Archilochus colubris) was illustrated as early as 1731. However, neither historical nor modern accounts accurately describe the feeding behavior of ruby-throats at trumpet creeper flowers or the floral adaptations for ornithophily. This paper explores their surprisingly immersive mode of foraging at trumpet creeper flowers and quantitatively assesses floral traits in two populations in the Ozark Mountains. The ruby-throat's bill is approximately one-third the length of the trumpet-shaped flowers, which counters the tendency for the corolla length of ornithophilous plants to match the bill length of their principal hummingbird pollinator. To reach the nectary, ruby-throats cling to the ventral petal lobe of the corolla with their claws and thrust their head and neck deeply into the flower. This immersive “floral-diving” has not been previously described among the 356 species of hummingbirds. The didynamous anthers and stigma are strategically positioned inside the corolla to brush the crown feathers when the ruby-throat inserts its head. A narrow stricture in the corolla, about a third of the way up, allows the bill and tongue of hummingbirds to pass, but blocks bees from reaching the nectary. None of the bee species native to eastern North American have tongues long enough to access floral nectar. Consequently, the abundant sucrose-rich floral nectar appears to be reserved for hummingbird pollinators.

This dataset presents measurements for 238 trumpet creeper flowers from two populations in the Ozark Mountains in Baxter County, Arkansas: (1) White River (36° 11.7ʹ N, 92° 16.9ʹ W; elevation 110 m) and (2) Norfork Lake (36° 22.5ʹ N, 92° 13.9ʹ W; elevation 177 m).