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Following article written by Kara Lefevre PhD (Ecology and Evolution / Environmental Studies, University of Toronto 2008).
Among the world’s natural environments, the rainforests of the New World tropics support the most plant biodiversity. The Monteverde Cloud Forest in Costa Rica is particularly known for its extraordinary plant life. The rich vegetation is due to high moisture levels and a wide range of habitats at different elevations. The result is a lush forest that supports layers of plants growing on plants, on every available surface.
“Epiphytes” are an integral component of rainforest ecosystems. These plants use host trees for support but derive nutrients otherwise, from their microenvironments. They are especially abundant at Monteverde.
Orchids are the biggest epiphyte family there (although not all orchids are epiphytic, with some being terrestrial herbs or climbers). These members of the large, global plant family Orchidaceae are famous for having complex flowers, whose stunning blooms are one of nature’s architectural masterpieces.
In fact, Monteverde has the highest known orchid diversity on earth. Amazingly, 34 species that are entirely new to science have been described there. The forest’s total number of orchids is thought to exceed 500 species, although documenting them all is a challenge because of their patchy distribution, often at great heights.
Plants are greatly influenced by the animalsthat distribute their pollen, and orchids are a perfect example. The anatomy, behavior, and movement of orchid “pollinators” affect the evolution of orchid floral morphology, and vice-versa. For example, the long “corolla” (the botanical term for all of the petals) of some orchids is thought to have co-evolved with long-tongued pollinators.
Orchids are often pollinated by insects, mainly bees. However, as if these flowers aren’t stunning enough on their own, another of their important pollinator groups is hummingbirds. Witnessing these tiny birds in action is one of the true delights of Neotropical forests, and Monteverde is no exception, hosting more than 30 species. They are appreciated for their dazzling, iridescent colours and remarkable acrobatics. So when these “jewels with wings” sip the nectar of orchids, the result is a visual symphony.
Hummingbirds are actually one of the few bird groups to specialize on nectar. This sugary liquid makes up most of their diet, with about one quarter consisting of spiders and insects. They have developed a relationship with orchids that benefits them both. The birds gain energy, and by transferring pollen among flowers, they create gene flow for each orchid species.
But plants and pollinators have opposing “strategies”. Hummingbirds need to obtain the most food with the least movement among flowers. Orchids need to obtain the most pollination with the least nectar output. This has led to co-evolution of anatomical features that further the goals of each party in the relationship. For example, natural selection favors curved flower shapes that draw in pollinators to pick up pollen, and also curved beaks to enhance feeding success.
Hummingbirds indeed have long, narrow bills and fringed tongues, perfectly suited for obtaining nectar. They also have adaptations for hovering, to be able to drink on the wing. They are the only birds that can fly in place, backwards and upside down, and so have extra-strong flight muscles. They also have a unique flight mode, rotating their wings in a figure eight instead of flapping like other birds. Their resulting energy demands are very high, producing the highest known avian metabolic rates compared to body mass.
Hummingbird-pollinated orchids tend to have brightly coloured flowers — think vivid reds, pinks, oranges and yellows. Their blooms are often have curved, with a design that allows enough space for hovering: that is, tubular, free-hanging, and a reduction in the distinctive, showy lip (“labellum”) that insects need for a landing strip. They are also typically odorless, as hummingbirds have a poor sense of smell.
It can be risky to be in an exclusive relationship. Plants cannot expect one type of pollinator to be omnipresent, and pollinators cannot rely on just one food source. A safer strategy is to be flexible: orchids often have several pollinators, and most hummingbirds forage among a number of flower species.
Field studies of the hummingbird community at Monteverde have documented fierce competition among the birds for nectar supplies. The birds can be aggressive defenders of flower-rich areas, such as some species of Amazilia. However, plants in the area have staggered flowering times, so blooms are available year-round to the dozens of hummingbirds of Costa Rica’s cloud forests.
The orchid flora is too voluminous to list, though here are some of the hummingbird species you may be lucky enough to spot sipping around Monteverde. The best time for general bird watching is during the dry season, from December to April. Prepare to be spellbound!
Blue-throated Goldentail (Hylocharis eliciae)
Brown Violetear (Colibri delphinae)
Cinnamon Hummingbird (Amazilia rutile)
Coppery-headed Emerald (Elvira cupreiceps)
Fiery-throated Hummingbird (Panterpe insignis)
Green Hermit (Phaethornis guy)
Green Thorntail (Discosura conversii)
Green Violetear (Colibri thalassinus)
Green-crowned Brilliant (Heliodoxa jacula)
Green-fronted Lancebill (Doryfera ludovicae)
Little Hermit, aka Stripe-throated Hermit (Phaethornis striigularis)
Long-billed Hermit (Phaethornis longirostris)
Magenta-throated Woodstar (Calliphlox bryantae)
Magnificent Hummingbird (Eugenes fulgens)
Plain-capped Starthroat (Heliomaster constantii)
Purple-crowned Fairy (Heliothryx barroti)
Purple-throated Mountain-gem (Lampornis calolaemus)
Ruby-throated Hummingbird (Archilochus colubris)
Rufous-tailed Hummingbird (Amazilia tzacatl)
Scaly-breasted Hummingbird (Phaeochroa cuvierii)
Scintillant Hummingbird (Selasphorus scintilla)
Steely-vented Hummingbird (Amazilia saucerrottei)
Stripe-tailed Hummingbird (Eupherusa eximia)
Violet Sabrewing (Campylopterus hemileucurus)
Violet-crowned Woodnymph (Thalurania colombica)
White-bellied Mountain-gem (Lampornis hemileucus)
White-tipped Sicklebill (Eutoxeres aquila)
References
Feinsinger P (1978). Ecological interactions between plants and hummingbirds in a successional tropical community. Ecological Monographs 48:269-287.
Fenster CB (1991). Selection on floral morphology by hummingbirds. Biotropica 23:98-101.
Kay KM, Reeves PA, Olmstead RG & Schemske DW (2005). Rapid speciation and the evolution of hummingbird pollination in neotropical Costus. American Journal of Botany 92:1899-1910.
Kricher JC (1997). A Neotropical Companion: An Introduction to the Animals, Plants, and Ecosystems of the New World Tropics. Princeton U Press, Princeton NJ.
Monteverde Bird Checklist http://www.exoticbirding.com/costarica/monteverde/checklist.html
Nadkarni NM & Matelson TJ (1989). Bird use of epiphyte resources in neotropical trees. Condor 891-907.
Nadkarni NM & Wheelwright NT (Eds). (2000). Monteverde: Ecology and Conservation of a Tropical Cloud Forest: Ecology and Conservation of a Tropical Cloud Forest. Oxford University Press, USA.
Siegel C (2011). Orchids and hummingbirds: sex in the fast lane. Orchid Digest, Jan-Mar:8-17.