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

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).