For flowering plants, entering into an evolutionary relationship with birds as pollinators can be a costly endeavor. It can take a lot of energy to coax birds to their blossoms. On the whole, bird pollinated flowers are generally larger, sturdier, and produce more nectar. They tend to invest heavily in pigmentation. The plants themselves are often more robust as well. Unlike hummingbirds, which usually hover as they feed, other nectar-feeding birds require a perch. Often this is simply a stout branch or a stem, however, a plant endemic to South Africa takes bird perches to a whole new level - it grows one.
Meet the rat's tail (Babiana ringens). Though not readily apparent, this bizarre looking plant is a member of the iris family. It is endemic to the Cape Province of South Africa where it can be found growing in sandy soils. It produces a fan of erect, grass-like leaves and, when conditions are right, a side branch full of red tubular flowers. This is when things get a bit strange.
From that flowering stalk emerges a much longer stalk that is said to resemble the tail of a rat, earning this plant its common name. This stalk rises well above the rest of the flowers. If you look closely at the tip of this stalk you will quickly realize this is yet another flower stalk, though this one is sterile. Such a stalk may seem like a strange structure for this plant to produce until you consider its pollinators.
The rat's tail has entered into an evolutionary relationship with a species of bird known as the malachite sunbird (Nectarina femosa). To access the nectar within, the malachite sunbird can't simply walk up to and shove its face down into the flowers. Instead, it must access them from above. To do so, it perches itself on the rigid sterile flower stalk. Once in position, the malachite sunbird can dip its long, down-curved beak directly into the flowers. This is exactly what the plant requires. In this perched position, pollen is brushed all over its chest.
Researchers wanted to know how obligate this relationship really was. By removing the perch on selected plants, they were able to demonstrate a reduction in pollination success . Specifically, male sunbirds were less likely to visit plants without the perch stalk. Although these plants are capable of self pollinating, like any sexually reproducing organism, outcrossing is the key to success. By offering the birds a sturdy perch allowing them exclusive access to their nectar, the plants guarantee sunbird fidelity.
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