Saturday, November 15, 2008

Devadatta argyoides

Competition to find a mate and reproduce the next generation is always very intense in the animal kingdom. Sometimes even a successful mating might not necessary guarantee the offsprings are sired by the original male.

Males of dragonflies and damselflies are especially adapted to displace the sperm of the previous male from a female. The discovery of sperm displacement in odonates by Prof. Jonathan Waage in 1979 is considered a significant finding in odonatology. Since then, it is now known there are four distinct ways a male can displace a rival male’s sperm: 1) physical removal by means of hooks or horns on the penis; 2) moving rivals’ sperm to sites in the females where its least likely to be used; 3) stimulation of female to induce sperm expulsion; 4) flushing out of rival’s sperm using the copulating male’s sperm.

These are fascinating behaviours. An earlier post mentioned this casually. Recently, I observed the copulation of Devadatta argyoides, enabling me a better understanding of sperm displacement.

Devadatta argyoides is from the family Amphipterygidae. This is a small and primitive family with only one species present in Peninsular Malaysia and Singapore. In fact Singapore is the type locality for this damselfly. It is rather common and usually found perching near small forest streams.

This couple had just gotten into tandem when I first spotted them. The male then flew with the female in tow for a short distance before perching above the stream. Slowly the female bent her abdomen to form the 'wheel’ thus interlocking their genitalia. Almost immediately, the male started displacing rivals’ sperm. This can be seen clearly by the male abdomen’s active movement. It lasted for about 2-3 minutes before the male stopped moving to transfer in his own sperm.


After copulation, the couple separated with the female flying off a distance away. The male did not seem interested in mate guarding nor did the female oviposit after I followed her for almost 10 minutes. I’m not familiar with the mating system of D. argyoides. Perhaps during this post-copulatory rest, the female was assessing the male’s guarding capacity, or the suitability of ovipositing site, or she’s manipulating the recently received sperm for fertilisation and evaluating its quality. The mating systems in odonates are varied with six systems currently recognised by scientists. There are lots more to discover on odonates mating behaviour especially species rarely encountered due to their elusive nature.



Pictures and video taken at: Bukit Timah Nature Reserve, October & November 2008



References:

Corbet, P. S. & S. J. Brooks, 2008. Dragonflies, HarperCollins Publishers, London, UK.

Lieftinck, M. A., 1954. ‘Handlist of Malaysian Odonata’, Treubia, vol 22, pp. 1-202.

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia

Sunday, November 09, 2008

Vestalis amoena; Vestalis amethystina


Vestalis amoena

Among Singapore’s damselflies, species from the genus Vestalis probably have the most attractive wings. Depending on the viewing angle and reflecting sunlight, the clear wings of these damselflies can appear to sparkle with purplish iridescence. We have two species in Singapore, Vestalis amoena and Vestalis amethystina. Both species look very much alike with the same metallic green colouration. In fact, the nine species known to exist in Sundaland are so similar in appearance that even differences in wings venation, body colouration and male penis structure are too ambiguous for species recognition. The only sure way to distinguish the species is by examining the male’s anal appendages.

Vestalis amethystina

Although it seems difficult but with a good digital camera giving a close-up shot of the male’s anal appendages, it is actually rather easy to identify our two Vestalis species in the field without having to capture them. For Vestalis amoena, the appendages are less curved towards each other and appear shaped like a horseshoe.

On the other hand, Vestalis amethystina has their appendages more curved towards each other. Females can be separated by the yellow labium of V. amoena and black labium of V. amethystina.

The geographical distribution of these two species is interesting. Both of them occur together from southern Thailand, Malay Peninsula to Sumatra. But V. amoena extends into Borneo while V. amethystina does not. In Borneo a close relative V. amaryllis, not found in the Malay Peninsula or Sumatra, exists. So it seems V. amaryllis became isolated in Borneo, differentiate into an independent species and occupies an ecological niche before V. amethystina could establish itself.

In Singapore, both V. amoena and V. amethystina occupy similar habitat: flowing streams in dense forest vegetation. However V. amoena is reportedly less common than V. amethystina. This seems to be very true as I encounter V. amoena less often during regular trips into the nature reserves. One very possible reason is that V. amoena prefers larger and faster flowing streams.
As forests degradation occurs, silt and sediments become accumulated causing streams to flow slower thus making it a more suitable habitat for V. amethystina. Historical records show that V. amoena was once found in Ulu Pandan. This is a perfect case in point of how much forests we have lost and how vulnerable forest damselflies are.



Pictures taken at: Central Catchment Nature Reserve, June 2008.



References:

Laidlaw, F. F., 1931. ‘A list of the dragonflies (Odonata) of the Malay Peninsula with descriptions of new species’, Journal of the Federated Malay States Museums, Singapore, vol 16, pp. 175-233.

Lieftinck, M A., 1965. ‘The species-group of Vestalis amoena Selys, 1853, in Sundaland (Odonata, Calopterygidae)’, Tijdschrift voor Entomologie, vol 108, pp. 325-364.

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia

Wednesday, October 01, 2008

Asian Toad

Singapore has about 24 native species of frogs and toads. The common species are of course very adapted to human landscape. They are more often heard than seen, especially after a period of heaving rainfall when males broadcast their desire for females. Occasionally though, a few individuals will stumble into our urban dwellings.

Few months back, an Asian Toad (Duttaphrynus melanostictus) made an appearance in my office. More precisely, it paid homage to a small corner. It was certainly a strange one. Throughout the whole time, it just sat there facing the wall with a contemplating look. It seemed overwhelmed by the wall and can’t decide what to do next. And it just stayed there the whole day and was so engrossed it totally ignored the mosquito sucking blood from its lower back.
There must be a scientific reason why it chose to sit at the corner throughout the day. But animals do strange things. Not all behaviour has to be explained and it is this erraticism that makes wildlife so fascinating.


Pictures taken at: National Biodiversity Centre, May 2008


References:

Baker, N. & K. K. P. Lim, 2008. Wild Animals of Singapore. A Photographic Guide to Mammals, Reptiles, Amphibians and Freshwater Fishes, Draco Publishing and Distribution Pte Ltd, Singapore.

Thursday, August 28, 2008

Drepanosticta quadrata

Damselflies from the family Platystictidae usually need close examination in particular the wings venation and anal appendages to identify the species confidently. Platysticids generally occurs in primary forests near small streams and the larvae have a distinctive disproportionately large head.
Within this family, the genus Drepanosticta is represented by eight species in Peninsular Malaysia. They usually fly close to streams, flitting within the forest understory. Both males and females typically have a blue spot at the abdomen base in which the shape of the spot can serve to identify some of the species from Peninsular Malaysia. Drepanosticta quadrata has a blue spot with a triangular pointed tip. This species was described from Singapore and according to references is known only from Singapore. This would thus make this damselfly a Singapore endemic. Even so, the website
http://www.asia-dragonfly.net/ has this species as also occurring in China and Myanmar and has pictures of females from Johor. More work is perhaps needed to shed light on the true distribution of this damselfly as Albert Orr himself noted Drepanosticta spp. as data deficient with many species needing identity clarification.




Pictures taken at: Central Catchment Nature Reserve, August 2008

Update 2010Jan19th:
The blue marking on abdominal segments S8-9 is variable among species of this genus. D. quadrata is not endemic to S'pore. In fact, it is believed that D. quadrata and D. fontinalis could be the same species. (thanks Dr. Ian Choong)


References:

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Orr, A. G., 2004. ‘Critical species of Odonata in Malaysia, Indonesia, Singapore and Brunei’, in Guardians of the Watershed. Global status of dragonflies: critical species, threat and conservation, eds, V. Clausnitzer & R. Jodicke, International Journal of Odonatology, vol 7(2), pp. 371-384.

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia

Sunday, August 03, 2008

Octopus species

This year is the International Year of the Reef and this coming National Day weekend, local marine lovers are having a series of talks and exhibitions to launch the event. This will be a great opportunity to highlight the amazing marine biodiversity Singapore has to the otherwise uninformed general public.

As part of the event, I’ll contribute an effort on this humble blog by drawing attention to the octopus, a creature which has always fascinated me with its amazing camouflaging abilities and known intelligence.

Octopuses can be found in a wide range of habitats. Many smaller species occur in rocky shores and coral rubbles where they forage in exposed pools during low tide periods. Most are excellent at camouflage and are able to match the colours of their surroundings with astounding dexterity. The video of this animal hunting says it all.


All octopuses use a strong neurotoxin at their salivary glands to immobilise prey when their long eight arms fan out into the nooks and crannies while hunting. The fast colour changes are presumably to camouflage it against predators although I remember reading somewhere that the changing colours are also a reflection of their ‘mood’.

Identification of octopuses to species level is not easy. Careful examination of their arm length; number of suckers; beak morphology etc is necessary. Nevertheless, small benthic dwelling inter-tidal species are from the family Octopodidae and this individual would be from the genus Octopus which most species belongs to. Many inter-tidal inhabitants are small. This octopus, with its arms fully extended, would be about the size of my two palms. For many people, all they see of octopuses is a blotch of black ink as the animal retreats into their hiding places at the first sign of danger. But any observer with patience and sensitivity will no doubt be rewarded with glimpses into the lives of our inter-tidal Singaporeans.

Happy National Day to ALL Singaporeans, big or small.




Pictures and videos taken at: A southern island of Singapore, July 2008


References:

Norman, M., 2003. Cephalopods. A World Guide. ConchBooks, Hackenheim, Germany.

Sunday, June 22, 2008

Pentaceraster mammillatus

It’s been almost two months since the discovery of a new sea star record at Cyrene Reef. Led by echinoderm expert Dr. David Lane, the find of Pentaceraster mammillatus created much excitement within local marine nature lovers. Not only that, the star created a chain of events, which I can now reflect on.

I'm heartened by the discovery not just because it’s a beautiful sea star, but more so that it was made from a combined effort of nature volunteers, government officials as well as a renowned scientist. All three parties whom are stakeholders working hand in hand for the betterment of Singapore’s natural heritage. As a result, Cyrene Reef now has a higher profile and has gotten the attention of the public. This is a major step towards creating a marine protected area for a reef with truly high biodiversity but also at the same time threatened by a busy shipping industry.

Publication of a subsequent news article on this discovery means everyone want a piece of the action. Many are eager to get associated, no matter how remotely, with this sea star. Working overtime editing the many drafts to satisfy all parties, the article was successfully published within a few days. For reasons known only to the perpetrator(s), the discovery also set off a series of flaming and argument on the Internet over basic taxonomy and even on the expertise of Dr. Lane. This has now resulted in what I can only best described as an uneasy truce among people working towards the same goal of marine conservation. How can we help nature when her very guardians are at odds?

Being previously found only in waters off eastern Africa and Red Sea region, P. mammillatus has been labeled an alien species by some. This is quite possible as Cyrene Reef is situated in the middle of Singapore’s shipping lanes and where ballast water could contain species not native to Singapore. This quickly became a thorny issue and politics soon came into play. To me, the wonderment of new discoveries is a major reason why I’m a student of nature. But when human politics interferes, my enthusiasm wanes quickly. I realise this is unavoidable and is something I would have to contend with. However, as much as possible, I shall do the science and leave the politics to the policy makers.

In retrospect, P. mammillatus had not only reinforced my love for nature’s possibilities but also gained me further insights into the different shades of human nature. Humans are after all nature’s child too.


Pictures taken at: Cyrene Reef, April 2008


References:

Clark, A. M. & F. W. E. Rowe, 1971. Monograph of the Shallow-Water Indo-West Pacific Echinoderms, British Museum (Natural History), London.

Wednesday, May 21, 2008

Prodasineura humeralis; Pseudagrion pruinosum

Some of the rarest damselflies in Singapore are restricted to the remaining forested streams in our nature reserves. It is always a pleasure to encounter them and more so to witness an intimate affair. I recently sighted two rare species at the same location along a clear flowing stream.

The first was Prodasineura humeralis. It is quite common in Peninsular Malaysia but in Singapore, it was first recorded only in 2006. The prominent linear orange markings are distinctive. There are several species from the genus with very similar orange/yellowish markings. In fact P. humeralis was previously listed as P. verticalis from Peninsular Malaysia so it seems there is a degree of interspecific and intraspecific variations. More work on the many species from this genus awaits further investigations. Prodasineura species usually perch in sunlit spots along forest streams and are in high densities where they occur. I saw three of them within the same area.

Just about 50cm away was a mating pair of Pseudagrion pruinosum. The intimate pair was oblivious to my presence thus enabling me to document their love tryst.

After about 10 minute’s copulation, the pair flew down to the stream and the female started ovipositing.

After a while, the male released his grasp and the female descended underwater.

The video clearly shows the female searching for ovipositing spots with her abdomen. She surfaced and flew off easily due to the fact that her forewings remained dry thanks to it being shielded by the closed hindwings.

Whilst the female was submerged, the male waited nearby on a leaf. The instant she surfaced, he grasped her again in eagerness for another round of mating.

This is the first time I witnessed such behaviour and am suitably thrilled. According to literature, underwater oviposition occurs only in endophytic odonates in particular the damselflies but this ovipositing mode is not a compulsory with regards to any particular species. Some advantages of underwater oviposition include exemption from interferences from males and protecting the eggs from desiccation.

Studying odonates has honed my patience and observational attributes. I eagerly anticipate the next exciting observation in the field.


Pictures and videos taken at: Mandai forest, May 2008.


References:

Corbet, P. S., 1999. Dragonflies: Behaviour and Ecology of Odonata. Cornell University Press, New York.

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia

Saturday, April 26, 2008

Rhyothemis phyllis

A large swarm of Rhyothemis phyllis was encountered recently. There was at least 50 or more individuals flying around within a small opening in the forest. This species is known to form large swarms where they engage in rather slow, gliding midair foraging. Aggregation of foraging dragonflies has been well reported by odonatologists. In fact mass swarms like this occur more often in lee situations where there is shelter from wind.


R. phyllis is one of the most commonest species and very easily recognised by its wing patterns. A close up shot allows me to examine the intricate details of its wings. In terms of aerial versatility and agility, dragonflies probably stand at the peak of flight evolution among the insects or even some birds. Two wing structures play a key role. The nodus helps in the elastic tension thus allowing strong twisting and also as a shock absorber. The pterostigma at the distal edge on the wings provides favourable pitching moments during wing flapping acceleration. This then raises the critical gliding speed where self-excited vibrations take place therefore enabling a more efficient wing stroke with less power expenditure.



While out on survey work, I’m always the one chasing after dragonflies. So it was a good change to have dragonflies flying all around me uninhibitedly.


Picture and video taken at: Western Singapore, January 2007 & April 2008.


References:

Corbet, P. S., 1999. Dragonflies: Behaviour and Ecology of Odonata. Cornell University Press, New York.

Norberg, R. A. 1972. ‘The pterostigma of insect wings, an inertial regulator of wing pitch’, Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology, vol. 81 (1), pp. 9-22.

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Thursday, March 27, 2008

Tyriobapta torrida

Females of different dragonfly species have different ovipositing modes. Scientists classify the different modes into three broad categories: endophytic (oviposition inside plants), exophytic (oviposition on anything except plants, which is water or substrate) and epiphytic (ovipositing on plants).

I’ve seen females ovipositing several times while out in the field. The most recent encounter gave me a chance to record videos of a particular female ovipositing in ultra speed mode.


This is the female of Tyriobapta torrida. She was flying in a circular motion at high speed and using the trajectory force to project water droplets and her eggs onto the water edge. Its amazing how fast she was flying and I can only imagine the aerodynamics involved. The lift and drag forces must be rather intense as well as the wings locomotion in overdrive to maintain the flight pattern. Not only that, she was going at it for almost 7-8 minutes. This is a lot of energy expended to produce the next generation. If only I can view this video in slow motion, which will certainly give an insight into the flight mechanics.


All the while, the mate-guarding male was hovering nearby. T. torrida males are easily recognised by the dark iridescent patch on the hind wing base. This species is rather common in our forests. T. torrida is the largest species within its genus. Where they occur, they are usually abundant with several individuals occupying and disputing small territories. Sexual activities are known to peak at around noon.


Corbet’s book described females from some other species diving underwater and ovipositing while submerged. Some species have been recorded to descend down to 1m depth. Now that is really a sight I want to behold.

This post is dedicated to Professor Philip Corbet who passed away on 13th February 2008 aged 78.


Pictures and videos taken at: Western Singapore, October 2007 & Venus Trail, March 2008.




References:

Corbet, P. S., 2004. Dragonflies: Behaviour and Ecology of Odonata. 2nd edition, Harley Books, Colchester.

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia

Saturday, March 22, 2008

Robber Fly

I was on Petai Trail recently and chanced upon this weird insect perching on a twig. It was motionless and thus perfect for a macro shot. It is about half the size of a palm and at first sight, looked rather fragile with its long abdomen hanging in mid-air. The poor insect seemed to be hanging for dear life.

It was only after I took a closer look at the picture and identification by Yixiong that I realised I’ve caught a glimpse of a fearsome predator of the insect world.

This is a Robber Fly from the Order Diptera (true flies). True flies are distinguished from other flying insects by having only a single pair of wings while their hind wings are greatly reduced into flight balancing organs called halteres. Robberflies belong to the Asilidae family but we are not sure what this particular species is.

Taxonomic classification aside, it is the ecology of robber flies that’s really fascinating. They prey on all sorts of insects, from easy ones like butterflies to prey that can put up a good fight like wasps, bees, spiders and dragonflies. In fact, some species are specialist hunters who target specific prey. Upon successful capture, a robber fly will inject its prey with saliva containing neurotoxin and other enzymes which immobilise the prey and liquify the tissue. Thereafter, the robber fly will suck on the soupy meal.

Not sure how well robber flies are studied in Singapore. But unsurprisingly, there’s tons of information on the web. This website
http://www.geller-grimm.de/general.htm is one of the more comprehensive.





Pictures taken at: Petai Trail, March 2008.


References:

Geller-Grimm, F., T. Dikow & R. J. Lavigne. Robber Flies (Asilidae).
http://www.geller-grimm.de/asilidae.htm

Sunday, March 02, 2008

Voluta nobilis

The second episode of Once Upon A Tree: Tides and Coastlines brought us back to nostalgic Singapore. Those were the days when people live much of their lives connected to the sea, for work as well as for play.

Work because, for example, The Raffles Hotel once stood just by the beach and would even be flooded during times of extreme high tides. Play, because trips to the sea then mean clear water, good fishing and excellent exploring on the seashore. The elders interviewed on the show mentioned big corals, huge fishes and dolphins were a regular sight. I’m quite sure one of the creatures they would have seen often too is this magnificent seashell, Voluta nobilis.


Voluta nobilis or “kilah” in the local language was once very common. They are now rarely encountered but still exists, mainly on our offshore islands. This pretty individual was spotted at Pulau Semakau recently. It’s been a while since I saw a live one, most of the time I found them as empty shells inhabited by hermit crabs. This individual’s siphon was fully extended as it searched for prey like bivalves. It will use its huge foot to suffocate and force its prey to open their shelves for oxygen. Once that occur, then its mealtime for V. nobilis.


Perhaps the elders from the documentary would be glad to know “kilah” can still be found in our waters.


Pictures and videos taken at: Pulau Semakau, February 2008.


References:

Tan, K. S. & L. M. Chou, 2000. A Guide to Common Seashells of Singapore. Singapore Science Centre, Singapore

.

Tuesday, January 22, 2008

Diplacodes nebulosa; Rhyothemis triangularis; Lesser Whistling-duck

Another odonate survey with the gang, this time to the ponds of Marina East. The habitat is dominated by thin grass-like vegetation. Not very sure what plant it is but most probably belongs to the Cyperaceae family. The water itself is full of brownish algae and there’s a slight smell typical of eutrophic waters.

Nevertheless, this is an excellent habitat for odonates. They are in high abundance and are very active thanks to the warm morning sunshine. The most numerous species is Diplacodes nebulosa. They are very distinct due to the dark tips on their wings. All the males are defending a small territory and chasing each other, zipping all over the water surface.

The most striking dragonfly there has to be Rhyothemis triangularis, aptly named due to the deep metallic blue triangular patch on its hind wings. Dragonflies from the genus Rhyothemis characteristically have short abdomens with broad hind wings. Some of them are quite common in open countries or streams in swampy forest. R. triangularis is common and widespread in Asia. However in Singapore they are rather uncommon as habitats akin to the Marina East ponds are few and far between.

But odonates are not the only creatures inhabiting the ponds. From afar, a Lesser Whistling-duck (Dendrocygna javanica) made an appearance. This is a nationally vulnerable bird. Once again habitat loss is the main cause as freshwater ponds are destroyed when urbanisation encroaches. This bird has an estimated population of 250 in Singapore.

As we left Marina East, I sensed a “melancholy in the wind and sorrow in the grass” (Charles Kuralt). How much longer will this location remain as it is? Its neighbour at Marina South is already morphing into the Integrated Resort. Rumour has it that Marina East will become a golf course. “Another golf course?!” Tang sighed.

Perhaps we could get the developers to build the golf course while preserving this small nature haven? My mind begins to sparkle…




Pictures taken at: Marina East, January 2008.


References:

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Wang, L. K. & C. J. Hails, 2007. ‘An annotated checklist of the birds of Singapore’, The Raffles Bulletin of Zoology, Supplement 15: 1-179.

Sunday, January 06, 2008

Purple Swamphen

We spent a relaxing Christmas afternoon in laidback Kranji countryside. After a sumptuous lunch, we headed to the farms dotting the area and as the sun began to set, we took a leisurely hike towards the Kranji Marshes.

The scenic Kranji Marshes hug along much of Kranji Reservoir’s perimeter. Marshlands are an increasingly rare habitat in Singapore as many have been lost to urban development.

As we took in the view, a series of loud chuckling and cackling greeted us. Out of a sudden, two dark purplish-blue birds with bright red bill emerged from the water vegetation. What a fortune! Its the unmistakable Purple Swamphens (Porphyrio porphyrio). I’ve previously only caught a glimpse of this elusive bird a year back so this was an excellent Christmas present from Mother Nature. Not only did the birds made an appearance, one of them was foraging uninhibitedly about 30metres away.

Purple Swamphen is a member of the Rail family which also includes the more common White-breasted Waterhen (Amaurornis phoenicurus). They inhabit mostly swampy and marshy habitats. These birds have a clearly distinguishable robust stout body, short tail and are rather weak fliers. Their huge red bill, red frontal shield, red legs and purplish-blue plumage make them one of Singapore’s most attractive marshland birds.
Purple Swamphens have a very conspicuous white undertail covert. The birds will constantly flash this white rump patch by jerking their tail up and down. Research suggests that this behaviour is a form of prey-predator communication whereby a bird’s state of alertness is communicated to a potential predator, thus discouraging the predator from a vigilant prey. Perhaps that was exactly what the bird was trying to tell us that Christmas afternoon. We certainly would not have the heart to harm such a fine-looking creature.




Pictures taken at: Kranji Marshes, December 2007.



References:

Alvarez, F. 1993. ‘Alertness signalling in two rail species’, Animal Behaviour, vol. 46 (6), pp. 1229-1231.

Robson, C., 2000. A Field Guide to the Birds of South-east Asia, New Holland Publishers (UK) Ltd, London.