Every dusk, thousands of white birds roost in trees on the island of Bali. This bird mecca is found in the rural village of Petulu Gunung just 3 kilometers outside of Ubud in central Bali. Historically, inadequate roads left the village of Petulu isolated and poor. Many people left to work in other parts of Bali to support their families. The region’s political turmoil exacerbated the local lack of economic development until Petulu Gunung’s villagers decided that it was time for them to take action against an unforgiving modern world. Together, on October 25th the village set out to perform a Buddhist ceremony that would bring them prosperity and growth.
The ceremony was called “Ngenteg Linggih,” and after the ceremony ended on November 7th, 1965, a group of Kokokan birds were observed nesting in the trees in Petulu Gunung. The villagers saw this as a positive sign and deemed the birds sacred animals that were not to be hunted or disturbed. The Kokokan bird became the Banjar’s (community council) symbol. As the weeks followed, more and more birds continued to make their way to the village to nest at sunset and leave again at sunrise.
The parting and arrival of the Kokokan birds became an extraordinary part of the daily lives of the villagers of Petulu Gunung. People from Bali and abroad came to see the famous nesting area and the beautiful flight of thousands of Kokokan birds [1, Personal Communication]. The influx of profit from this sustainable eco-tourism project provided the banjar with moderate economic prosperity and the money for adequate roads to allow access in and out of the village.
Is this mass flocking a holy Buddhist phenomenon? Or can science explain the sheer numbers of birds?
The science available tells us that many bird species flock at dusk to avoid predation [2,3,4, 5]. Being in large numbers makes it more difficult for predators to go unnoticed and can confuse predators. This can make it more difficult for them to attack . Another interesting reason birds roost together is that roosting areas act as “information centers” so that birds can exchange feeding locations and warnings . Lastly, for some birds, roosting in a large flock reduces the amount of energy needed by each individual bird to thermoregulate .
While it is possible that this colony has come to roost in Petulu because of the Buddhist ceremony that drew prosperity and growth to their village, it’s more likely that the safety provided to the birds by the local banjar developed the area into a safe habitat that deterred predators and which was conveniently close to a food source (rice fields). However, a scientific study on this particular colony’s behavior could illuminate the precise reasons for this phenomenon.
What exactly are Kokokan birds?
The Balinese clump 3 different species of birds together in the name category of “Kokokan”. This includes the Cattle egret (Bubulcus ibis), the Plumed Egret (Ardea plumifera), and the Little Egret (Egretta garzetta). The Blekok bird (Javan Pond Heron, Ardeola speciose) is also occasionally sighted by the locals and visitors and bears great significance because of its rarity .
These 3 species of Egrets are quite similar in that they are all smaller than cranes or herons and they all have white plumage. All three have a similar body shape. They have a short but thick neck and relatively short legs compared to their relatives, the great heron or grey heron. There are also subtle differences that can be observed between the three [7,8,9,10,11].
The Cattle egret stands out because of its short dagger-like yellow beak and yellow legs and feet. They have a relatively short neck and medium-length, broad, rounded wings. During breeding season, their plumage becomes gold on their head, chest and back [8,9].
The Plumed Egret is similar in size to the Cattle Egret. The Cattle Egret also has a stout yellow beak. However, during breeding season the beak becomes reddish in colour. Their necks are approximately the same length as their body and are held in an “S” shape. Another interesting change during breeding season is that their facial skin near their eyes turns green in colour [9,10].
Lastly, the Little Egret is similar to the Plumed Egret in that they have the “S” shaped neck and similar plumage. However, they are set apart from the two other egrets because they have a sharp pointed black beak and black legs, but yellow feet. They are smaller in size as well. In addition, they also have a small plume of feathers that extend beyond the head making. This of course is only based on outward appearance; however, research has shown them to be genetically different as well .
On top of bringing tourists to Petulu, these Kokokan birds have an agricultural benefit. They prey on insects, lizards and other pests that inhabit freshwater areas such as rice fields. One study in Italy found that 80% of Egrets’ diets were sustained by agricultural habitats . Essentially, they act as good pest control . What is also fantastic is that there will never be a shortage of these three species of egrets as their conservation status is of “Least Concern” and in some cases, their populations are rising [8, 10, 11].
So, what happens when you get approximately 10,000 egrets nesting in a small village on the island of Bali? Aside from a LOT of bird poop (on the street, trees, cars, and occasionally on an unlucky person) the village of Petulu Gunung is a mecca for Bali’s beautiful and elegant Kokokan birds. Beyond providing the opportunity to see these magnificent birds, this eco-tourism project is sustainable and has brought prosperity to the people of the village. The women from Petulu village have started a small business collective making fine Balinese arts and crafts to sell as souvenirs and the cost of admission and parking covers the payment for local guides. So, if headed to Ubud, the Balinese center of yoga, meditation, and health, why not make a stop at this flocking phenomenon.
 Banjar Petulu Gunung. Petulu Gunung Objek Wisata: Kokokan (Heron Bird Colony). Brochure.
 Emlen, J. T. (1952). Flocking behavior in birds. The Auk, 69(2), 160-170.
 Beauchamp, G. (2004). Reduced flocking by birds on islands with relaxed predation. Proceedings of the Royal Society of Biological Sciences, 271(1543), 1039.
 Hogan, B. G., Hildenbrandt, H., Scott-Samuel, N. E., Cuthill, I. C., & Hemelrijk, C. K. (2017). The confusion effect when attacking simulated three-dimensional starling flocks. Royal Society Open Science, 4(1), 160564.
 Ward, P., & Zahavi, A. (1973). The importance of certain assemblages of birds as “information‐centres” for food‐finding. Ibis, 115(4), 517-534.
 Beauchamp, G. (1999). The evolution of communal roosting in birds: origin and secondary losses. Behavioral Ecology, 10(6), 675-687.
 BirdLife International. 2016. Bubulcus ibis. The IUCN Red List of Threatened Species 2016: e.T22697109A86454050. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22697109A86454050
 Allaboutbirds.org. (2015). Cattle Egret. Retrieved from: https://www.allaboutbirds.org/guide/Cattle_Egret/id
 BirdLife International. (2016). Ardea plumifera. The IUCN Red List of Threatened Species 2016: e.T22727683A94956915. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22727683A94956915
 New Zealand Birds Online. (2013). Plumed Egret. Retrieved from: http://www.nzbirdsonline.org.nz/species/plumed-egret
 BirdLife International. 2016. Egretta garzetta. The IUCN Red List of Threatened Species 2016: e.T62774969A86473701. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T62774969A86473701.
 Siegfried, W. R. (1971). The food of the Cattle Egret. Journal of Applied Ecology, 8, 447-468.
 Mohammedi, A., Doumandji, S., Ababou, A., Koudjil, M., & Rouabhi, A. (2016). Impact of predation by cattle egret Bubulcus ibis L. on wildlife of farmlands in Chlef region, Algeria. Lebanese Science Journal, 17(2), 117.
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