A Handsome Native Plant: Columnea polyantha and its Pollination Strategy
Hirsute leaves of the epiphyte Columnea polyantha, a native Gesneriad
Anyone who ever cared for African Violets already knows the family of flowering plants called Gesneriaceae. There are no species whatsoever in that family native to the United States or Canada, as it is a largely tropical family, but here in Costa Rica there are 27 genera and 140 species. At Finca Cantaros on the Pacific highland side of the Talamanca Mountains, we are fortunate to have the prolonged wet conditions that allow at least two native Gesneriads to grow wild: Drymonia macrantha and Columnea polyantha. I find both extremely attractive, but Columnea polyantha is the subject of today’s post because I just learned something new about it recently: its principal pollinator.
Flowers of Columnea polyantha.
The seeds of this plant are excreted onto tree limbs, into small indentations of the trunk bark, or onto climbing vines by birds that have eaten the fruit of C. polyantha. The seedlings then grow as epiphytes, their roots taking advantage of the trees without being harmful parasites. Noting the shape and color of the flower, you have probably guessed that C. polyantha is pollinated by hummingbirds. But which one(s)?
C. polyantha is hirsute all over except for the main stem. During the flowering season (February to early June here) the dark red hairs of the upper side (lamina) of its leaves attract hummingbirds’ attention as they fly over in the forest understory. The birds descend to investigate and find bright yellow tubular flowers extending pertly under the leaves. The little red accents on the flowers’ entrance lobes entice them further to drink the nectar within. However, as often as I have passed this plant during the four to five months it is blooming, I’ve never managed to arrive when a hummingbird is feeding. With 18 species of hummingbirds on the Finca Cantaros bird list, 12 of which are reasonably common, this bad luck mystified me. The plant seems to shout out for hummingbirds, and I was getting more curious daily.
Flower and fruit of Columnea polyantha
Enter doctoral students Jessica Anne Greer, Adam Hadley and their adviser, Matthew Betts, Ph.D of the Forest Landscape Ecology Lab at Oregon State University. At the nearby Wilson Botanical Garden and at other sites over the past three years during our region’s dry season, the team has literally counted pollen grains of different plant species collected from the beaks of hummingbirds captured temporarily in mist nets. While the team was using our property for a control study this field season, looking at visitation of hummingbirds to a wild heliconia common here, I asked whether they happened to know which hummingbirds visit C. polyantha. Several weeks later, Jessica had time to study the data for three field seasons at other sites, 2012-2014, and she generously gave me a report.
Green Hermit, male, visiting Heliconia flower. Photo: Andrew Russell.
Of the 22 species of hummingbirds they captured and released over three years, only 3 species carried pollen from C. polyantha. Both the Violet Sabrewing and the Green-crowned Brilliant carried a very small amount of pollen (averaging 2 grains per bird), while the Green Hermit carried a much higher pollen load (averaging 105 grains per bird). They recorded one individual Green Hermit with 1564 grains of C. polyantha pollen! It seems clear that the Green Hermit has the highest potential to pollinate based simply on the number of pollen grains carried. It has a very long beak, compared to the other two hummingbirds: it seems better suited to reach the nectar deep within the long tubular flowers. Of 33 individual birds carrying this pollen, 29 were Green Hermits.
Mystery solved. We can now say with some assurance that Green Hermits are the C. polyantha’s best friend–its main pollinator. Next year I will make myself a blind and simply sit long enough to witness an actual pollination event at this strikingly beautiful plant.
Green-crowned Brilliant, male. Photo: Andrew Russell.
Green Hermit, female, visiting a Costus flower. Photo: Andrew Russell.
Violet Sabrewing, male. Photo: Andrew Russell.
Evidence of nectar robbery at base of flower. Suspect: Stripe-throated Hermit. Jessica Ann Greer also mentioned that when positioning a camera here at Finca Cantaros for a few days next to one of the C. polyantha plants, a Striped-throated Hermit flew up to visit a flower, but then flew off due to the human intrusion into its territory. These birds are known as nectar robbers, making holes in the sides of flowers to steal nectar, not going the usual route that involves making contact with pollen. After the Oregon State researchers have an opportunity to review all its data from the field cameras at their Wilson Botanical Garden and other study plots, they will have more information about exactly which hummingbirds might be acting as nectar robbers and not pollen carriers of Columnea polyantha.
Guest photographer and friend Andrew Russell of Heredia, Costa Rica, generously granted permission to use his photographs of the Green Hermit, Violet Sabrewing and Green-crowned Brilliant.
Reference: Gesneriads of Costa Rica by Ricardo Kriebel Haehner. Instituto Nacional de Biodiversidad (INBio), Costa Rica, 2006, pp. 11, 148.
Babblers in Borneo
1. Chestnut-winged Babbler on left observes vigorous activity of potential mate.
It took a trip to Borneo for me to learn about cooperative breeding in birds, a system of reproduction used by only about 3% (300 species) of bird species worldwide.
As guests of close friends from the San Francisco Bay Area, my husband and I were most fortunate to visit Sabah, Malaysia in northeastern Borneo in April to see some of the most biologically diverse habitat in the world. From the Kinabatangan River floodplain with its abundant wildlife, to the spectacular Dipterocarp forests of Danum Valley, the tallest of all tropical rainforests, we focused on birding. Nature itself, and very competent guides, provided thrilling opportunities to see many other orders of wildlife as well, including many endemic to Borneo.
You may recall in my last post in March I discussed the lekking behavior of Orange-collared Manakins, a regional specialty here in southwestern Costa Rica where I live. Males gather, select a forest area that females are known to visit, and prepare an arena on the forest floor, where they perform impressive mating rituals. The female selects the most attractive or able performer and off they go to breed. It may be a one time fling.
In the case of Stachyris erythroptera bicolor, the Chestnut-winged Babbler, a flock of which we encountered in the forests near the Sukau Rainforest Lodge, we were able to observe activity that was completely unfamiliar to us: up to six birds were engaged in what appeared to be a complex activity. Impossible to know for sure which was male, and which female, as I later learned the sexes look very similar. Birds seemed to display and then hide blue skin patches around the throat. In each of three pairs, one individual–probably the male– shook its body vigorously and suddenly darted away, closely followed by the observer to another nearby branch. Activity was going on concurrently by the different pairs within a two square meter area, and all under observation from above by a small gallery of an adult and two juveniles. Those birds were very vocal, as were the performers.
2. The bird on the right in photo #1 above, next flies up to a higher branch.
3. Intense shaking by bird on lower branch (about three feet above the ground) seems to stimulate the upper bird to fly to a new position. It lands close by.
4. These birds–like spectators–are perched higher than the birds in the photos above and are singing and changing positions to watch all the activity below.
Center singing bird may be teaching offspring the appropriate songs for such occasions.
Fascinated by the degree to which the birds were so intensely engaged in their activity, I photographed from close by without seeming to perturb the birds. When one performer suddenly flew away, all the other birds dispersed as well.
Back at home I learned that breeding by these Babblers occurs in Borneo between March and July. Group activity of 4 to 26 birds is common for insect foraging in middle and understorey plants in rain forests up to 1200 M. Nests are built by both sexes, but there have been observations of up to four birds building a single nest. Some species of well-studied other Babblers practice cooperative breeding, where offspring help parents raise more offspring without breeding on their own. The non-parental adults helping the breeding pair are called “extra-pair helpers”, “auxiliaries” or “supernumeraries”. The Handbook of the Birds of the World could only say that Stachyris erythroptera bicolor is “probably multi brooded” and are “partly social breeders”. Clearly more research is needed. In some systems of cooperative breeding Stanford researchers found that dominant females succeed in monopolizing reproduction in a group. Female offspring stay near to help as subordinates, but their reproduction is rare. All new to me.
It would be very interesting to know exactly what was going on during those charming early afternoon performances, but in any case it was a magical experience for us all.
Note: The Chestnut-winged Babbler’s range is from extreme southern Burma and Thailand to peninsular Malaysia, Sumatra and Borneo.
References
del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.) (2016). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/ on 16 May 2016).
Cooperative Breeding by Paul Ehrlich, et al, 1988, Stanford University
The Sibley Guide to Bird Life & Behavior, pp. 566-567.
The Elusive Orange-collared Manakin
Orange-collared Manakin male in woods at Finca Cantaros
One of the most interesting aspects of living in a nature reserve is that opportunity to observe animal behavior frequently arises. Sometimes an expert comes along to open the windows wider on behavior that previously seemed random and mysterious, if it was noticed at all.
Take the case of the Orange-collared Manakin, a 4” (10 cm) bird endemic to our region that fortunately prefers to frequent low levels just above the forest floor. I knew that males gather to lek each year in small groups of two or three. In the lek system of mating (known as polygyny), it is the female that selects and pursues the male, and the male provides no parental care to its young. The males aren’t passive, however! They perform intricate displays, vocal and visual, to lure females to a neutral location—sites with presumably high female traffic. Their performance determines whether they merit being selected for mating.
In polygyny, whether among Topi Antelope, California Sea Lions, Moor Frogs, Lake Malawi Cichlid fish, or different Manakin species, including the Orange-collared, males can mate with multiple females. No permanent bonds are formed. The most attractive or the most vigorous males will get to do the majority of the mating, while the subordinate males may do no mating at all.
Orange-collared Manakin near the prepared “arena”
I knew the male Manakins display for females between January and March by making loud buzzing noises and snapping sounds with their wings, almost like the breaking of dry twigs. When I first heard this sound years ago I thought some animal was walking in the forest nearby. It took knowledgeable birders to reveal the source of the sound.
Over time with binoculars I managed on occasion to see males zipping with startling speed from sapling to sapling in a specific area of the forest. The only way to see them was to listen first to the buzz-snaps, and then to focus on the area from a respectful distance and hope to see the male’s stunningly bright orange collar, puffed during courtship. The female Orange-collared Manakin is mostly olive-green, with the belly an olive-yellow, and is difficult to spot. I knew also that we had three different areas around the property where the buzz-snaps occur and where courtship takes place each year. With great frustration, I had tried to photograph the males, but had been unsuccessful. They moved too fast, and I couldn’t get close enough.
Last year a researcher named Matthew Fuxjager—who had been studying Golden-collared Manakins in Panama—visited Finca Cantaros; he opened that window for me to learn more about the Manakins. He showed me three different “arenas”, circles about a meter in diameter on the forest floor, where the males had cleaned away leaves to create that neutral location for their displays. Matthew explained that the females watch the displays of prowess from above, and then fly down to the arena close to the preferred male. The pair then fly off to copulate and reproduce.
Lek arena prepared by male Manakins at Finca Cantaros.
Since taking photographs from a distance produced only blurry images, this year I decided to sit near an arena and take my chances that the birds might ignore me if sat quietly nearby. The strategy worked to a point. This year’s dry season (January to March) has been unusually hot and dry due to El Niño, and the Manakins were quiet until early March. They are unpredictable: I sat for three different hours at different times of the day over a week’s time, but no Manakins approached the prepared arena. On the fourth attempt they did come to the arena at 11:00 AM. Finally, after years of trying, I was finally able to get the above shots.
Previous efforts to photograph the Orange-collared Manakin male met with blurry results.
During bird banding days at Finca Cantaros this male Manakin was captured and released in February, 2016.
A banded female Blue-crowned Manakin is very similar to the more olive toned female Orange-collared Manakin.
References:
Foto Diarist 