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Bat Pollination In Thailand: A Decade of Research Online Webinar.

20 May 2021

On the 13th of May 2021, WWF Thailand, with support from GO organics Peace International, Earth Net Foundation, and Heinrich Böll Stiftung Southeast Asia, held the latest in the series of ongoing webinars on pollinators. 

Organised together as the Asian Pollinator Initiatives Alliance (APIA) the webinar aimed to raise awareness on the importance of pollinators and to encourage actions to conserve them. 

The May webinar was titled, 'Bat Pollinators in Thailand, a Decade of Research' and was hosted by Assistant Professor Dr Alyssa Stewart of Mahidol University who has been studying bat pollination in Thailand since 2011. 

When pollinators are discussed, people often think of bees and birds, bats are often overlooked. This webinar is  the first in the series to be focused on bats and highlighted their importance, especially for a tropical country like Thailand where many fruits rely on bat pollination. 

About Dr. Stweart, 

Dr. Stewart first became interested in ecology as an undergraduate student, when she was an exchange student for a year at Mahidol University. After completing her Ph.D. in Ecology at the University of Maryland, USA, Dr. Stewart moved to Thailand and has been working at Mahidol University for the past five years.

She is interested in all aspects of plant-pollinator interactions, and continues to study pollinators large and small (from bats to bees), and across a broad range of habitats (from wild to agricultural to urban).’ With a decade worth of experience and research, Dr. Stewart brings a vast amount of information, knowledge, and expertise to the topic. 

Dr. Stewart’s research focuses mostly on pollinator biodiversity and conservation. Some of her on-going projects include studying the pollinators of native plant species, studying the factors that promote pollinator diversity in urban environments, and studying the effect of chemical pesticides on pollinators. 

Some Learning Points from: Bat Pollination in Thailand, a Decade of Research with Dr. Alyssa Stewart an APIA webinar, by Michael Commons. 

Michael Commons from Earth Net Foundation, who co-organised, combined his personal experience and dicussions with Dr. Alyssa along with the key points from the webinar to write the following learning points. 
  1. Regarding bat species in Thailand, many species are insectivores.  Some species primarily eat fruit but also feed on nectar.   3 species exclusively feed on nectar, and 4 other frugivorous species often visit flowers.
  1. While fruit eating bats may help with pollination, most of the pollination work is by these 3 nectar feeding species.
  2. We can easily visually distinguish between the fruit-loving and nectar-feeding species.  The nectar-feeding species have much longer noses and tongues, well-developed to get into flowers and lap up nectar. The fruit eating species  have shorter snouts and tongues.
  3. The nectar-feeding pollinator bats in Thailand (and the whole old world) have large eyes well-developed to see at night, but very limited echolocation ability1.  They use their eye sight to find the flowers.  New world pollinator bats in the Americas do not have these large eyes and use echolocation to find flowers for foraging.
  4. The fur of all bats easily collects a lot of pollen2, A1.   In a personal conversation, Dr. Alyssa shared that these bats will clean off their fur with their tongue, eating a lot of pollen as well.  She thinks this may be a key source of protein and their total diet for bats that otherwise feed only on nectar.
  5. For plants primarily dependent upon bat pollination, their flowers have developed to work well for the needs of nectar-feeding bats.   The flowers are generally high up (in the tree) and thus accessible. The flowers are strong enough to easily hold the weight of the bats which cling to the flower / stalk and then lap up nectar.   The flowers are of colours that are easily visible at night, normally white or cream, to be seen by the bats' large eyes.   The anthers are located so that they will deposit pollen on the fur of the bats when they collect nectar, some distance from the stigma where nectar is collected.  (In fact Dr. Alyssa showed how different bat pollinated flowers deposit pollen on different areas of the bat such as the chest for Parkia, or face from durian, which then as shown in their research meant that most pollen transfer was to the same genera.) Most all of these flowers bloom early in the night and drop off in early morning thus matching the bats foraging cycle.   Dr. Alyssa also shared in a personal conversation, when I imagined how much nectar a decent-sized bat would need to consume compared to much smaller bees and moths, that these flowers produce a lot of nectar and are often dripping with nectar when in bloom. 
  6. In her research, Dr. Alyssa found 6 genera of plants that are highly dependent upon bat pollination in the South of Thailand.  These are durian (Durio),  kapok (Ceiba),  bitter bean (Parkia), banana (Musa), sky tongue (Oroxylum), and lampoo (Sonneratia)3.  These species are all important in Thai culture and life.  Durian is favourite fruit, kapok is used to fill pillows and mattresses such as the famous triangle pillows of Issan, bitter bean or “sator” is a very popular vegetable in the South to Thailand, sky tongue or “phega” is another popular vegetable particular in the North and Issan regions, lampoo is a key mangrove tree that is famous as being a favourite tree of fireflies, and bananas of course are so important in many ways4.
Eonycteris Sonneratia © Merlin D. Tuttle

Eonycteris Oroxylum © Merlin D. Tuttle

  1. While durian and kapok produce a lot of flowers and nectar seasonally, each at a different time, the other genera tend to flower more or less year-round.   Lampoo is constrained to mangrove areas primarily with brackish water, whereas the other genera are widely spread.
  2. While there are 7 species of nectar-feeding bats in Thailand, according to her research, they do not all effectively pollinate these 6 genera of bat dependant plants.  Some plants are highly dependent upon one or more species.  In her studies the most effective and thus critical pollinator for some genera including durian and kapok is the Cave Nectar Bat, Eonycteris spelaea.
  1. As her research showed such a high dependency on this bat species for pollination and fruit set, and this species resides in caves,  I asked if I have good fruit set yet live distant from any caves that I know of, does this mean my flowers are being visited by these bats?   Dr. Alyssa said that it is very possible that they are as these bats can fly 40 km to forage5, although they might also be being pollinated by tree-roosting fruit bats.  As I am quite sure there are caves within 40 km “as the bat flies”  from my garden, I will need to observe more.
  2. In Dr. Alyssa's research on bat populations through collecting information on visitations, it was clear there is a lot of variation year to year.   While she finds the research not yet sufficient to make any clear conclusion, the data she has from 2019 and 2020 finds much lower visitation numbers for some bat pollinator species than when she started her research about 10 years ago.
  3. One particular area of concern is with mangroves and lampoo (Sonneratia) which is highly dependent on bats for pollination.   Loss and degradation of mangroves, also means loss of habitat and fodder for the bats.  With fewer bats, pollination and fruit set is reduced, thus further weakening the mangrove and its ability to recover.  So this is a vicious cycle.   As one participant asked about data on bat population in mangroves, Dr. Alyssa said there is not much data at all and data would be valuable but difficult to collect.  Just collecting data on bat visitations requires working at night and normally high up in the canopy where the bats forage. In mangroves this would be further complicated by doing this same work in the water and silt of the mangroves.

Additional Questions

            Last as our overall objective is “pollinator restoration”  I asked “If we want to do pollinator friendly gardening- for bats- is this just as simple as planting some of these 6 species? And perhaps not harvesting our banana flowers early to let the bats feed longer?"  (on the male flowers which continue to bloom for some time).
Dr. Alyssa responded, “For more rural areas, yes, definitely. For more urban areas, it's also important that the bats have roosting areas too. I think it is unlikely that we will find the Cave Nectar Bat (Eonycteris spelaea) in Bangkok because they roost in caves. But I have seen Cynopterus bats visiting Phega flowers at the Faculty of Science in Phayathai. These bats mostly eat fruits but also visit flowers, and they roost in various species of palms (and likely other plant species too), and I think they probably roost at Suan Chitlada (which is right behind the Faculty of Science) because it has lots of plants. I have also observed Cynopterus bats roosting in some palm trees in the middle of Prince of Songkla University's campus (in Hat Yai). So it seems like these bats aren't all that deterred by human activity, they just need a place that has enough roosting plants and food plants.”
            Then I asked "Is there a strong preference for bats for wild bananas or a certain variety- like Nam Wa. (I have only found seeds in wild bananas and Nam Wa personally.)"
Dr. Alyssa responded, “They like all banana flowers, both wild and cultivated! So planting any variety of banana will provide food for the bats.  Most banana cultivars can't produce seeds (even when they receive pollen) because they are triploid (so when the genetic material is divided during meiosis, some cells get two copies of a chromosome and some get only one, and then during fertilization the chromosomes can't pair properly). Nam Wa is also triploid, but for some reason it can produce seeds when it receives pollen from a wild (diploid) banana. (I'm not sure why.)”
Final thoughts 

            Coming out of this webinar, I feel I have a much better understanding about bat pollination in Thailand and how we can help promote bat pollinator populations as well as areas which I think would be interesting to further explore.  The six genera of plants that are in such a key relationship with bat pollinators are really useful and interesting plants.   If we look from a Permaculture design perspective and different and complimentary values, these genera have a lot to offer.   I intentionally planted many phega or sky tongue trees, which grow like long tall stick with few leaves and thus take up almost no space or light.   I enjoy eating the pods, roasted on a fire first, then peeled and sometimes cooked again in a stir fry.   While I have yet to identify any nectar-feeding bat genera, I regularly see bats come to feed on their flowers.  Bitter bean- parkia, is a leguminous, nitrogen fixing tree, with giant pods of beans.   For me it is another favorite vegetable, which satisfies like meat and thus may be a good choice for vegetarians.  Durian is one of the most amazing fruits.  While from Dr. Alyssa's research almost all of the pollination is done by bats, their flowers are also much visited by Apis dorsata honeybees being an important source of nectar6.  Kapok produces pods full of soft fibers that can be used for stuffing.  I heard from another bee researcher that their flowers also provide a lot of nectar for honeybees.   Bananas are an amazing fruit, and vegetable.  Banana flower salad is one of my favorite dishes.  Wild bananas are one of the most favored foods of wild elephants.  Bananas also are a famous helper species plant, providing moisture, mulch and microorganisms to nearby plants as Jon Jandai recounts in his book on gardening.  While it is more difficult to grow, I remember so well my first night time boat ride in Ampawa about 18 years ago and the lampoo trees lit up life Christmas trees all along the sides of the waterways we passed through.   I also much appreciate the small grove of lampoo trees in Santichaiprakan park next to the Chao Phraya River in the heart of Bang Lampoo.
            As the Cave Nectar Bat is such a key species, while Thailand is blessed to have karst limestone mountains all along its backbone which have many caves,  I wonder as to the habitat needs of these bats.   I recall when I lived in Barcelona years back and would walk by Camp Nou, the grand stadium of FC Barca at night, that there were quite a number of bats that would feed around the street lights and appeared to be coming from somewhere in the stadium.   My presumption was that part of this massive concrete structure was functioning as an artificial cave and habitat for the bats.   If Cave Nectar Bats can or do also reside in artificial caves, then building or maintaining such spaces may serve for their habitat needs where natural caves are not present.
            Staring our pollinator journey looking a lot at the different Apis species as well as stingless bees, it was really great to connect with a very different groups of pollinators.   Dr. Alyssa's presentation also brought more to light how different pollinators have relationships with different plants.   So while flowers may be visited by a variety of pollinators, successful pollination may be highly dependent on one species.  With this in mind I look forward to learning more about other key pollinator species like hawkmoths, carpenter bees, and honey creeper birds to understand both their relationships with different plants and which plants are highly dependent upon their work, and then about their habitat and other needs, so that we may better manage our spaces to provide them good places to live.
            By Michael B. Commons,  Earth Net Foundation, May 2021

1. https://socialbat.org/2015/01/27/studying-bat-pollination-in-thailand/
2. Muchala, Nathan et Al, “Fur versus Feathers: Pollen Delivery by Bats and Hummingbirds and Consequences for Pollen Production” The American Naturalist, Volume 175, No 6, June 2010
3.  https://socialbat.org/2015/01/27/studying-bat-pollination-in-thailand/
4.Personal experience/ knowledge of the author
5. START, A. N. 1974. The feeding biology in relation to food sources of nectarivorous bats (Chiroptera: Macroglossinae) in Malaysia. Ph.D. Thesis, University of Aberdeen, Aber - deen, Scot land, 247 pp.
 6. Prasit Wongprom shared about Apis dorsata and durian flowers in his webinar session with APIA

Additional notes from Dr. Stewart. 
A1 This interesting study showed that bat fur holds much more pollen than bird feathers: https://www.journals.uchicago.edu/doi/abs/10.1086/652473

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