Diversity of echolocation

Hackett et al. 2013, echolocation calls of 13 species in the Arava Desert, Israel.

When I first saw the figure above, I realised how incredible the diversity of bat calls was. Of course, I had noticed this diversity before, without actually never taking the time to wonder why that was. Yet, this figure only shows a fragment of the diversity found in bat echolocation calls.

If echolocation always serves the same purpose, why such a diversity? Does it actually always serve the same purpose?

But first, what is echolocation?

Echolocation: definition

Echolocation is a sense, just like sight and hearing, helping the animal to perceive its environment. However, unlike those two senses where signals come from the environment (light and sounds), an animal must actively produce a sound to detect objects in its surroundings. So it’s an active sensor. Echolocation has several purposes: spatial orientation, identifying the animal’s surrounding habitat (linked to the presence of certain prey) and finding food (Denzinger and Schnitzler, 2013)

Bats aren’t the only animals using echolocation. There are three other groups capable of doing so: Odontocetes (a fancy word to say dolphins and relatives), some birds and…humans…though we need fancy technology for that!

Bats and Cetaceans (Dolphins and whales) are very different. The first fly, are usually tiny and feed on insects, fruit, nectar and what not, whereas dolphins and whales rely on water for their survival, feed mostly on fish and krill and can grow to be the biggest animals ever to have lived on this planet. Bats are also significantly more diverse than cetaceans with just under 1400 species described so far compared to around 70 species. Yet, both groups have developed this unique ability. Why would two very different animal groups need the same highly specific sense? The answer: visibility, or lack thereof.

Bats are mostly nocturnal so visibility is very poor when they’re at their most active. Many Odontocetes dive deep, beyond the reach of sunlight or live in murky waters such as in rivers. In those conditions, sight is pretty much useless so an alternative is needed to locate prey. Echolocation allows them to forage in a wide range of less easily navigated habitats.

There are very few species of birds capable of echolocating, namely the Oilbird (Steatornis caripensis) and a few species of Swiftlets (Aerodramus spp.). This ability allows those species to roost deep inside caves, far from most predators. (Brinkløv et al 2013)

Not all bats echolocate. Until recently, bats were split in Microbats and Megabats (Figure 1B).

The distinction was mainly based on size but it also happened that only the former group echolocates. The currently accepted classification is Yinpterochiroptera and Yangochiroptera (Figure 1A).

Interestingly, this leads to two different hypotheses on the evolution of echolocation. Either it evolved in the common ancestor of all bats and Pteropodids (fruit bats) subsequently lost it (and some Rousettus developed a new way to achieve a similar result), or it evolved twice, once in the Rhinolophoid group and once in the Yangochiroptera group (Springer 2013).

Figure 1:  Currently recognised bat taxonomy (1A, top) and its previous iteration (1B, bottom)
Figure 1: Currently recognised bat taxonomy (1A, top) and its previous iteration (1B, bottom)

Amongst the Pteropodidae, the biggest family of non-echolocating bats, several species of the genus Rousettus are known to produce clicks using their tongue (Roberts 1975).

Recent research has also shown that some members of the family are capable of echolocating with their wings! (Boonman et al. 2014)

That’s all great but why such a diversity?

I’m certain all of you have at one point or another in your life, have found yourself in a busy shopping mall, or café. How easy is it to have a normal conversation in there? Not that easy at all! That’s because all the sound waves are interfering with each other, resulting in a despicable noise.

Now, replace the humans in the shopping centre with bats. And turn off the lights. All those bats have to find food, listening to their own echo to picture their environment. Wouldn’t be easier if each bat has its own characteristic echolocation call?

While that’s not the case, strong variability between species allows different species to find different kinds of prey in the same environment, without disturbing one another.

Small bats will usually have a call of high frequency because it gives them the resolution required to find small prey whereas larger species will usually look for larger prey, thus having a lower call.

The specialised calls of Hipposideridae and Rhinolophidae work in a different way. They have a constant frequency and the bats listen for modulations in that frequency in the echo. Those modulations are the result of the Doppler effect. If you don’t know what that is, you’re far from the only one. But also, you do know what it is. When you hear an ambulance, you know if it’s in front or behind you. The sound changes as it goes past you. That’s the Doppler effect, in very short. If you want to know more, the internet is a much better teacher than I am.

This highly specialised method allows them to perceive the flutter of the flying insects, enabling them to not only distinguish a flying, living prey from a falling leaf but also to distinguish between different types of prey.

 
What about bats of the same species then?

Well… They also want to find food and avoid collision. What bats of the same species will usually do is slightly modulate their frequency to avoid interference. They will also emit “social calls” aimed at reminding the intruder that it’s their turf. Not so social after all.

A few interesting examples

What’s that funny looking nose for?

Ever looked at a photo of a Horseshoe bat or a leaf-nosed bat and wondered what that weird, somewhat ugly nose was for? Well…as said earlier, those bats have developed their echolocation differently than most other “microbats”. The sounds are still produced in the larynx, nothing new under the sun. What’s different though is that the sound then goes through the nose where it is focused into a narrow beam. This gives extreme precision, but also a low visibility range.

Tricking the moths that don’t want to be tricked

Picture this, bats hunt moths. Moths develop hearing to avoid bats. Bats find way to trick the moths into thinking the danger is much further than it actually is. Isn’t that amazing? Well, that’s the somewhat simplified story of the Barbastelle bat, Barbastella barbastellus. Instead of producing a series of single calls that moths with “ear drums” can easily locate, Barbastelle bats produce pairs of low intensity calls, at different frequencies. Because of the low intensity, the moths aren’t alarmed until it’s too late. It’s tricked into “thinking” that there are two distant bats instead of one Barbastelle right on its six. The combined information gathered from the two calls makes up for the lower intensity.

Form follows function

In Europe, two common species are the Common Noctule (Nyctalus noctula) and the Common Pipistrelle (Pipistrellus pipistrellus). Their calls vary significantly. Noctules hunt above the canopy and are fairly large so are mainly looking for larger prey. Pipistrelles hunt below the canopy, in more cluttered habitat and are very small so are looking for really small prey (mosquitoes!). A Noctule’s call is long and quite low in frequency, giving it plenty of range, but poor resolution. A Noctule also won’t be emitting the calls too quickly one after another as the collision risk is very low. A Pipistrelle’s call on the other hand needs to have high resolution and be emitted frequently to avoid collisions, so it’s much higher in frequency and much shorter.

On the diversity of accents

I’m sure we’re all familiar with slight language variations between countries, or even between regions inside a country. These variations are known to use as accents. Similar variation has been described in birds, such as the Chaffinch, Fringilla coelebs (Slater et al. 1984). Interestingly, geographical variation has also been described in bats, especially in constant frequency call emitting species such as Rhinolophus spp. and Hipposideros spp. At this stage, it’s not yet known whether it could be cryptic diversity (species where genetic data can show more diversity than morphology alone) or if it is indeed, geographical variation. Hopefully, future research will be able to answer that question! 

Sonogram of examples of calls of all echolocating groups of animals (and humans, who don't echolocate) (Brinkløv et al 2013).

Further reading

Bats of Philippines

Kiwi, my travel companion amazed by the sheer size of Acerodon jubatus, the largest bat in the World!
The view on the beach near the Underground River on Palawan.

Looking for bats in Oceania (e.g. New Caledonia, Australia) was relatively easy: the literature is fairly easy to find; the bat fauna isn’t too diversified; and a number of people had visited the areas before, making it quite easy to follow in their steps. But this was all about to change as I flew to the Philippines. With no literature available, barely any research having been done there at all, high species diversity and very few people visiting this archipelago for its bats, the challenge ahead was substantial!

With over 7,000 islands, I had to choose as I had only planned a 16-day stay in the archipelago. As a general rule, the larger the island, the higher the diversity, so I knew I wasn’t going for the really small ones. However, while Luzon is the biggest one, it’s also one of the most degraded islands, meaning that most species of bats would be in inaccessible parts, yet to be destroyed (which let’s be honest, is their likely future). In the end, I decided to choose Palawan, because it’s still quite wild and because of its Underground river, home to 8 species of bats; Mindanao to visit Monfort Bat Sanctuary; and Bohol because I found reports of bats in easily accessible caves there. At the beginning and at the end of my trip, I spent a bit on time on Luzon.

First destination of the trip was Subic Bay, North of Manila. Known to birdwatchers and mammal watchers alike, the place is famous for its Large Flying Fox, Pteropus vampyrus and Golden-crowned Flying Fox, Acerodon jubatus colony. The two species are competing for the title of largest bat in the world, although the latter seems to be the largest in most cases. Either way, they can have a wingspan north of 1.6m, that’s 5 ft 3’ for the non-metric folks out there. It’s crazy!

On my arrival to the known place, no bats to be seen. After asking a couple of locals, I discovered that the roost had burnt, driving them deep inside the jungle. Not good news… Turns out that bats really are creatures of habit though, because they came back to feed on their usual trees a little after dark. Not a great sighting because of the darkness but what a relief!

With my bat recorder, I managed to identify a few microbats, including the Asian wrinkle-lipped Bat, Chaerephon plicatus that I will see over and over again throughout my journey across SE Asia, Pipistrellus javanicus and Rhinolophus philippensis.

Megaderma spasma, evidently not amused by me trying to take its portrait...
Cynopterus luzonensis waiting for the day to go by, hiding under a palm leaf.

On Palawan, I stayed in Sabang, away from the busy city of Puerto Princesa. Although I should say that describing PP as busy makes it a bit of a struggle to find the appropriate word to describe Metro Manila. With over 13 million people, which is more than Belgium (okay, not the biggest country in the world, I’ll give you that), how do you imagine traffic is? The M25 (near London) is a breeze to cruise in comparison with downtown Manila…

Sabang is also very busy. Well, it has more chickens than people and these are responsible for most of the traffic on the road but still. It’s also where the Underground River is located. The Puerto Princesa Underground River, or PPUR in short is an extremely touristic place but is still home to thousands of bats. I had to visit it.

 

During my first visit, I left my bat recorder running during the entire cruise (on small paddle long boats. Nice and quiet, unlike the boats they use to get you there from Sabang…) and recorded a number of species, most of them were known from the cave but not all. I am still working on some identifications at this stage so I won’t yet list the species I recorded.

After the cruise, I paid a visit to Chucky, the local and very friendly Palawan Peacock-pheasant.

I decided to go back the next day to take some photographs of the bats to help with the identification process. Thousands of Hipposideros diadema, many Rhinolophus spp, especially close to the entrance (R.philippensis, R.creaghi and R.acuminatus) as well as some Miniopterus roosting in small groups.

Every night, I recorded the bats around Bambua nature lodge, where I was staying (highly recommended btw) and managed to add a couple more species.

I also did a couple of days of birdwatching with Will Cabanillas, an amazing guide! I really recommend him if you’re visiting the island, and you should, its bird life is amazing!

Female Colugo, the Philippine Flying Lemur, closely related to Primates.
Emballonura alecto. I really like those bats, they always look like they're smiling!

Next stop, Mindanao to visit the island of Samal and the Monfort Bat Sanctuary. The Sanctuary hosts a complex of shallow caves, full of bats. The caves are only home to a single species, Rousettus amplexicaudatus but it’s a rare example of bat based ecotourism so I had to visit it. Sadly, bat ecotourism hasn’t really picked up (yet?). It would be great if that could be changed in the future! I definitely recommend visiting the place if you’re in Davao.

Onto Bohol next, I stayed in Lobok, close to the nature attractions the island has to offer and stayed at the Water to Forest Ecolodge (also highly recommended. Although it wasn’t as cheap as Bambua, it was equally good value).

From there, I visited the Butterfly Conservation Center. You could definitely give that one a miss, if it wasn’t for the cluster of Cynopterus luzoniensis roosting under a leaf inside the park. I did consider visiting the Tarsier Conservation Center but the entrance was as crowded as Disneyland so I skipped that one.

I visited some caves in the Raja Sikatuna NP where I found the diminutive Hipposideros pygmaeus. Seriously, it’s tiny! I also saw many more Hipposideros diadema and a few Miniopterus. During every cave visit, I leave my recorder running, so I still have to identify some of the bats here too.

I also visited a cave behind the Butterfly Conservation Center with the help of one of their guides. That one had the same species but also had the endemic Greater Musky Fruit bat, Ptenochirus jagori .

Kiwi posing in front of the entrance of the bat cave at Monfort Bat Sanctuary, home to 1.8 million fruit bats!
Hipposideros diadema wondering why suddenly it's daytime inside its cave.
Chaerephon plicata exiting one the lecture halls on the University of Philippines campus in Los Banos.

For my last ‘usable’ night in Luzon, I decided to visit the Philippine University campus of Los Baños. I had been told bats were emerging from one of the buildings and it’s also a birdwatching hotspot so I thought I’d give it a go. The bats emerging from one of the lecture halls were Chaerephon plicatus, about a thousand or so. For the rest, bat activity was very low. No fruit on the trees so no fruit bats but also none of the highlights of the place such as the Hornbills and Malkohas.

Identification of my sound recordings is likely to take a while and it will be an ever bigger challenge with the recordings I’ll make in Indonesia. But I’ll get there and I’ll make sure to keep you updated!

Overall, during my stay in the Philippines, I saw/recorded 27 species of bats, which is a lot more than I anticipated.

Flying Kangaroos

When you think about it, in Australia, marsupials have equivalents for pretty much all kinds of mammals (or used to). There are anteater-like marsupials (Numbat), squirrel-like marsupials (Gliders), mole-like marsupials (Marsupial moles), cat-like marsupials (Quolls) and there even have been rhino-like (Nototherium) and panther-like species (Thylacoleo) (now both extinct) but there has never been a bat-like marsupial. Shame… I think it would be really cool to have a marsupial bat… Imagine a little head poking of out of a pouch of an already really cute bat…

Juvenile Spectacled Flying Fox thinking about its future life, away from an unlimited supply of fruit...
The view at sunset from O'Reilly's. If you look closely, there should be a Pademelon or two.
The one and only furry diving log, the Duck-billed Platypus. Possibly the weirdest mammal on Earth.

After visiting all those small-ish Pacific Islands, such as Viti Levu, Guadalcanal and Grande Terre, I had to start seriously increasing my species list at some point. The easiest way to do that was to go to Australia. Australia is well known to be home to a whole range of creatures capable of killing you but it’s also home to many cute and harmless creatures as well. Amongst those are marsupials and bats, on which I focused, obviously with more attention to the latter.

Australia has 80-ish species of bats. The taxonomy of a number of groups is still very much poorly understood so this number could well go up in the near future.

Most of those are present in either Queensland, Northern Territory, or both. Naturally, I decided to visit those two states. Visiting the other states, while interesting wouldn’t have left me enough time to visit each of the places I wanted to visit.

Orange Hipposideros ater inside its matching coloured cave.

In Queensland, I first spent a couple of nights in Brisbane where I met Vanessa, who’s doing a PhD on bats in culverts (check out @i_live_in_a_culvert on Instagram to learn more about her research) and Luke, from the Botanical Gardens, both keen bat watchers. My first night in Australia was bound to be a success. And indeed it was, with 8 species seen/recorded not far from Mt Coot-tha. We missed Myotis, surprisingly. In fact, bat activity had pretty much died by 9pm…

During the following 10 days, I explored Tropical North Queensland. Having been hit by a storm a few days prior to my arrival, many roads were still closed and it was raining most days, albeit not constantly. This limited my opportunities to see and record bats. On top of that, I spent the majority of those days without a detector due to a technical failure. Some of the highlights include the Tube-nosed Bat (Nyctimene robinsoni) I saw up in Cape Tribulation and the tiny cave full of Hipposideros ater at Bramston Beach (campground, the owner is a great guy. Definitely worth a visit, either for the bats or for the view from the campground. Or both). Previous reports of Orange Leaf-nosed bats are this site are wrong. Some bats are indeed orange, that doesn’t make them Orange leaf-nosed bats though, a species absent from Queensland. 

I also visited the Tolga Bat Hospital. In November 2018, a heat wave struck North Queensland, combined with the seasonal tick paralysis outbreak, it left 900 Spectacled Flying Foxes orphaned. Tolga had 700 in care when I visited. There are few words to describe the people who work there, other than heroes. If you have a chance to visit, do. If not, visit their Facebook page and maybe consider making a small donation to help their titanic work! They truly deserve it.

Juvenile Spectacled Flying Foxes enjoying their time in the aviary at Tolga Bat Hospital.
A bower of a Satin Bowerbird. Mostly plastic but the diversity of objects is incredible.
One of the things that won't kill you in Australia, a Feather-tailed Glider

After that, I flew to Darwin for a few days. I got a new detector on my second day there, having been sent a replacement unit under warranty. Great job from Wildlife Acoustics and Faunatech! Up there, I visited Litchfield National Park, Tolmer Falls in particular as they are known to be home to Ghost bats (Macroderma gigas) and Orange Leaf-nosed Bats (Rhinonicteris aurantia). I saw the former, but unfortunately not the latter. Ghost bats are carnivorous and feed on amphibians, small mammals, including bats. Orange Leaf-nosed bats are understandably not too comfortable having a hunting Ghost bat nearby…

I also visited Fogg Dam. I had been told it was good for birds and bats but also for Crocodiles! I still hadn’t seen one and I didn’t want to leave the country without seeing one… Batting was outstanding, with no fewer than eight species recorded from the dam itself. Of course, being CrocWise, I didn’t leave the safety of my car. The dam was also the hunting ground for a couple of Night Herons and a handful of Barking Owls. As for the crocs, well, I did well not to leave my car as I saw a few, none really big though.

Kiwi, my travel companion and a lovely view of Tolmer falls.
A teddy bear surprised to have been caught after escaping a child's room. AKA, Lumholtz's Tree Kangaroo
Deadly stare of an appropriately named Death Adder

When I arrived in Australia, I hoped to reach 50 species on my overall list, I was then at 19. It was ambitious but doable. When I had to send my detector for repairs, that goal seemed unrealistic. However, by the time I left Darwin, I had reached that magical number! Best of all, I still had a couple of nights left in the country!

I visited Mt Glorious but didn’t get a lot of bat activity, the rain probably didn’t help. The next day, I visited O’Reilly’s. They used to run the Mammal Week there, one week where the goal was to see any many mammals as possible. So the bat fauna in the area is quite well known. Bat activity was okay but the diversity wasn’t great. I still managed to add two more species to my list, Chalinolobus morio and the Golden-tipped bat (Phoniscus papuensis).

Of course, one cannot visit Australia without looking for some of the strangest mammals on Earth. I saw 19 species of Marsupials, Kangaroos, Wallabies and Possums. The highlights were the Striped Possum in Curtain Tree Fig, the Lumholtz’s Tree Kangaroo at Nerada Tea Factory and the trio of gliders (Greater, Yellow-bellied and Feather-tailed) I saw with Alan. That day, up in the Tablelands, I also met John Harris. Both Alan and John are great naturalists. If you happen to be visiting either Queensland or Victoria, make sure to get in touch with them!

Leaving the very best for the very last, I had the chance to accomplish a childhood dream, seeing a Platypus.

As usual, contact me for GPS coordinates or more information on locals contacts.

Full list of bat species:

  • Mt Coot-tha: Chalinolobus gouldi, Mormopterus ridei, Saccolaimus flaviventris, Pteropus alecto, Rhinolophus megaphyllus, Austronomus australis, Miniopterus orianae.
  • Perrin Park : Pteropus poliocephalus
  • Cairns township: Chaerephon jobensis, Pteropus conspicillatus
  • Cape tribulation: Mormopterus beccarii, Chalinolobus nigrogriseus, Pteropus scapulatus, Nyctimene robinsoni
  • Bramston Beach: Hipposideros ater. Previous reports of Orange Leaf-nosed bats are inaccurate, that species is not present in Queensland. Significant colour variation among the bats in that cave, some were bright orange.
  • Tablelands: Myotis macropus (under the bridge in Yungaburra, good spot for Platypus), Nyctophilus gouldi, Vespadelus pumilus, Nyctophilus bifax, Hipposideros semoni.
  • Litchfield NP: Macroderma gigas
  • Buffalo Creek: Nyctophilus daedalus, Pipistrellus westralis, Vespadelus caurinus
  • Fogg Dam: Scotorepens sanborni, Pipistrellus adamsi, Nyctophilus walkeri, Taphozous georgianus, Taphozous kapalgensis, Nyctophilus geoffroyi, Nyctophilus arnhemensis

O’reilly’s: Chalinolobus morio, Phoniscus papuensis

 

Full list of mammal species:

  • Duck-billed Platypus Yungaburra
  • Short-beaked Echidna Julatten (dead)
  • Northern Brown Bandicoot Darwin (dead)
  • Striped Possum Curtain Tree Fig
  • Yellow-bellied Glider Tablelands
  • Lemuroid Ring-tailed Possum Tablelands
  • Northern Greater Glider Tablelands
  • Green Ring-tailed Possum Tablelands
  • Feather-tailed Glider Tablelands
  • Short-eared Brush-tailed Possum Brisbane
  • Common Brush-tailed Possum Brisbane
  • Lumholtz’s Tree Kangaroo Tablelands
  • Mareeba Rock-wallaby Mareeba
  • Red-legged Pademelon Tablelands and Curtain Tree Fig
  • Eastern Grey Kangaroo TNQ
  • Agile Wallaby Fogg Dam
  • Common Wallaroo Chillagoe
  • Giant White-tailed Rat Tablelands
  • Red-necked Pademelon O’reilly’s
  • Whiptail Wallaby O’reilly’s (on the way back)
  • Black-striped Wallaby O’reilly’s (on the way back)
  • Common Ringtail Possum O’reilly’s

Bats of New Caledonia

France in the Middle of the Pacific

I really could not think of a better way to describe New Caledonia. And sadly, I do not mean this in a good way. After visiting Fiji and Solomon Islands, what a shock it was to land in New Caledonia. Apart from the climate, vegetation and the occasional Coconut Lorikeet flying over, there isn’t much to separate this from France. The people there are, unfortunately, quite far from having the kindness of heart of the people of the rest of Melanesia. As for the true Melanesians, they seem to be considered as inferior because of their way of life. Visiting a village in Poya reminded me a lot more of Guadalcanal than the rest of New Caledonia.

But you did not come here to hear me rant about this country, you came to learn about bats.

Sunset over Nouméa and the ocean nearby that I had visited while scuba diving earlier that day.
The very cute Yellow-bellied Flyrobin, endemic to New Caledonia.
View from deep inside the Park de la Rivière bleue, where I saw most of the endemic bird species.

On my first evening there I went up to Koghi, one of the few places where Nyctophilus nebulosus has ever been sighted. This extremely rare bat has rarely been observed, and its echolocation call has never been recorded. I was lucky enough to record it and even see it hunting. The identification of the call was fairly straightforward as it is the only Nyctophilus on the island and the calls of that genus are very distinctive. I compared my recordings with recordings from Australia where there are a number of Nyctophilus species. Another endemic, Chalinolobus neocaledonicus was also present as well as Miniopterus spp. According to the literature, M. australis and M. macrocneme are indistinguishable based on recordings. That is possibly due to a lack of research. Further down the road, on the way back to Nouméa, I had a few more contacts of Miniopterus spp, which seemed to be really enjoying the many street lights.

The New Caledonian bat fauna comprises 9 species, of which one, Miniopterus robustior, is restricted to Lifou and Ouvéa, two small offshore islands, to the North of Grande Terre, the main island. Of the remaining eight, I had seen two already, Pteropus tonganus and Miniopterus australis. Given than M. macrocneme isn’t reliably identifiable by its call, that meant I could see a maximum of five new species, all of them endemics.

The echolocation call of Nyctophilus nebulosus (with Chalinolobus neocaledonicus).

I managed to get to Poya and a nearby cave that is home to Notopteris neocaledonica, the New Caledonian Blossom Bat, a species closely related to the Fijian Blossom Bat I saw a couple of weeks earlier. Access to the cave was quite easy and it didn’t take me long to find them. The cave was also home to hundreds of Satin Swiftlets, they even had chicks. Once again I enjoyed the show of the Swiftlets navigating the cave using echolocation. I also discovered it was rather ineffective as I was hit repeatedly. Also present was a Barn Owl. Was it roosting in the cave or simply having a lunch break? It’s hard to tell. Judging by the number of feathers on the ground, it definitely wasn’t the first time a Barn Owl showed up in the cave and snatched a few Swiftlets! It is likely that they eat bats as well.

In a nearby cave, I found Miniopterus spp. as well as Chalinolobus neocaledonicus, a species not known to roost in that cave. This cave also had the most bizarre living organism I saw that day: plants growing in complete darkness. Yet, their leaves were greenish so they were producing chlorophyll. It could be that at some point in the day, light hits the cave just right and the plants get sunlight. I also found a rather cute gecko, as yet unidentified.

Notopteris caledonica, a vital pollinator for both crops and wild plants.
The biggest Flying Fox roost in New Caledonia, home to 10,000+ bats!
One of the caves I visited, home to hundreds of swiflets and a few bats.

In the evening, I visited the biggest Flying Fox roost in New Caledonia. The roost has Pteropus tonganus, P. ornatus, an endemic and the rocks below are home to P. vetulus, a small endemic flying fox favouring roosts under rocks or in caves. A census during the non-breeding period revealed that there were 9,000 bats roosting there. At this time of year, we could be anywhere north of that. Your guess would be as good as mine!

What a great way to end this trip. On the bat side of things, this trip was a success! As for the rest, I definitely will not go back…