By Ralph Simon
In October of 2011, Merlin, his wife Paula, and I, accompanied by National Geographic science writer Susan McGrath, began the incredibly difficult task of, for the first time, documenting a wide range of highly specialized flower adaptations to facilitate bat visitation in Costa Rica, Cuba, and Ecuador. Following three months of little sleep, red tape, floods, terrible roads, and seemingly endless searches, we finally were able to photographically document the amazing adaptations of very special plants, echo vines, old man’s beard cactus, and sea bean vines, which attract nectar bats with their acoustics (original project report).
Nectar bats must make hundreds of visits to flowers every night to find enough nectar to survive. As one can imagine, finding small flowers in the dense vegetation of a tropical forest can be challenging. But plants have evolved exceptional adaptations to help bats find their flowers. First, they provide special odors, often like garlic, cabbage, or sulfur, not attractive for humans but bats love them! Many bat-pollinated flowers have thick, waxy surfaces that reflect exceptionally strong echoes, helping bats use echolocation to find them from greater distances.
A few flowers even provide conspicuous echo-reflectors to help guide bats to their nectaries. These reflectors stand out through a wide radiation pattern, which means that bats receive loud echoes audible from many directions. They basically work like an acoustic cat’s eye (retroreflector). And they also reflect a unique spectral signature, like a fingerprint, which bats can easily identify. Behavioral experiments show that if these reflectors are missing or blocked with a piece of cotton, the flowers are rarely visited by bats, demonstrating their importance.
The most specialized flowers are found in relatively stable, tropical areas. In locations where climate and associated pollinators are less predictable, many plants hedge their bets by opening at night but remaining open and receptive for some or all the following day. This serves as insurance in case bats don’t visit. The rare echo vine (Marcgravia evenia) is such a species. It grows in low abundance in some of Cuba’s densest tropical forests. Bright red, and frequently visited by hummingbirds, it was long believed to be mainly hummingbird-pollinated.
A Leache’s long-tongued bat (Monophyllus redmoni) pollinating Marcgravia evenia in Cuba, and a Cuban emerald hummingbird is getting a free meal without pollinating. The upturned leaf reflects bat echolocation, guiding their approach like airport landing lights guide pilots at night. In fact, neither insects nor hummingbirds are large enough to contact the plant’s reproductive organs, so even when they find Marcgravia flowers, they rarely achieve pollination.