Caring for Pollinators - Bundesamt für Naturschutz

Schuchmann Fact sheet pollinators: Avian pollinators: Hummingbirds, Sunbirds,
Honeyeaters, Hawaiian Honeycreepers (Trochilidae,Nectariniidae,
Meliphagidae, Carduelidae)
The evolutionary relationship between hummingbirds and their food plants is a good
example of close mutualism, resulting in the many adaptations between flower and pollen
vector that together is called ornithophily. Plants that have converged upon the
“hummingbird” syndrome bear relatively large flowers, solitary or loosely clustered, often
placed in a horizontal or pendent position. Typical hummingbird plants open their blossoms
during the day: the flowers are generally brightly coloured, often red, orange or yellow,
sometimes in combination with contrasting white corolla parts. Exceptions can be found in
the Gesneriaceae, where some epiphytic species exhibit solitary inconspicuous whitisch
flowers. However, hummingbirds are attracted to these well-camouflaged flowers by their
ornamental red-edged or red-centered leaves, a little studied advertisement strategy in
hummingbird-pollinated plants known as phyto-flagging.
The corolla of a typical hummingbird flower is often long, thickened, tubular in shape, and
scentless. It contains sucrose-rich nectar which is taken by trochilids in hovering or hoverclasping
flight. Many characterisitics of hummingbird-pollinated flowers, such as red colour,
lack of odour, or the floral tubes with their thick walls, are adaptations either to avoid
attracting insect competitiors or to prevent nectar robbing. Ornithophily seems to be
energetically expensive for plants. Although the energetic expenditures of plant reproductive
strategies are still poorly understood, it is most likely that this process is energy-demanding.
The evolution of ornithophily must therefore be viewed from from the perspective of costs
and benefits, obviously well balanced between hummingbirds and their plants.
Due to their relatively high body mass hummingbirds have a much higher potential mobility
than most insects. Foraging distances of more than 1 km have been reported for trochilids
visiting widely distributed flowering shrubs in a single feeding bout. For most insects the
travelling distance between successive flower visits tends to be much smaller and foraging
strategies are much more stereotypic. A long-lived pollinator such as a hummingbird
experiencing several flowering seasons during its lifespan, combined with the capacity of its
excellent spatial memory, can easily remember localy or patchily flower stands. Thus, the
floral environment for trochilids is much more differentiated in time and space than for
insects.
Main flower preferences
Hummingbirds pollinate about 30% of all Neotropical angiosperms. In cloud forests (c. 1000-
2500 m), where trochilids are the major pollinators, up to 60% of the local angiosperm
population may depend on hummingbirds as pollen vectors.
Common and well-studied hummingbird-pollinated species belong to the genus Zauschneria
(Onagraceae), Delphinium and Aquilegia (Ranunculaceae), Mimulus (Scrophulariaceae),
Aphelaria (Acanthaceae), Centropogon (Lobeliaceae), Psamisia and Cavendishia
(Ericaceae), Psittacanthus (Loranthaceae), Heliconia (Heliconiaceae).
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