Exploring New Guinea’s Rich Diversity of Amphibians and Reptiles

Fred Kraus

Fred Kraus writes about his work to discover new species of reptiles and amphibians in the wet tropics of Papua New Guinea.

Fig. 1 - Fred Kraus
Fig. 2 - Fred Kraus
Fig. 3 - Fred Kraus
Fg. 4 - Fred Kraus
Fig. 5 - Fred Kraus
Fig. 6 - Fred Kraus

Jimmy was clearly upset. That seemed an unusual way to start the day, and inquiry revealed the reason to be that our three hired local assistants had disappeared during the night, leaving us alone in the forest. A search turned up two of them, huddled in fear along the trail leading back to the village, a position in which they had spent the night. After asking, Jimmy learned that the previous evening, while we should all have been going our separate ways in the forest collecting frogs, Atelus, the third, missing, assistant had convinced these other two that I had put a spell on him. The evidence for my new-found power was that he had felt the wind blow against the back of his neck three times when I insisted that he turn off his torch as I recorded a new species of frog that was calling for a mate; lights disturb the calling frogs. Upon recording and capturing the frog, Atelus and I parted ways, at which point he frightened our other two assistants with his story, and the three ran back down the trail toward the village on a moonless night, without headlamps. Atelus made it all the way back to the village, warning others of my nefarious powers, but the other two eventually gave up the mad, blind rush, leaving them for Jimmy to discover trailside in the morning.

This was a serious spot to be in. Virtually everyone in Papua New Guinea professes adherance to one Christian sect or another, but this is usually only a veneer over a deeper, abiding belief in sanguma, or black magic. So such a charge was not to be taken lightly. And we had only finished constructing our camp the day before, starting our collecting the evening of this supposed event. By 10:00 a.m., as expected, half the village swarmed into camp to assess the situation. By that time, our two remaining local assistants had calmed down and, upon prodding from Jimmy, admitted that they had not witnessed me practicing any black arts but had merely responded to Atelus’s fear and slightly distorted narrative. In discussions with the newly arrived villagers, these fellows’ support of my innocence – as well as the reasoned argumentation from our friend Telon, one of the respected older men in the village – convinced everyone that nothing had in fact happened, and we were allowed to continue our work in the forest. By the end of this two-hour discussion, Atelus too sheepishly admitted that nothing had really happened. He also asked to be re-admitted to his former position in the camp, but that seemed a rather foolhardy thing to agree to. So I didn’t.

How could I get myself in such a position? It’s simple: I conduct scientific surveys to discover and describe new species of reptiles and amphibians in Papua New Guinea (PNG). This country forms the eastern half of the island of New Guinea and includes as well a number of adjacent islands to the east. The country retains one of the largest percentages of tropical rainforest remaining in the world, making it very important for conservation of tropical biodiversity, but its biota is poorly known relative to that of the better-studied Neotropics, Africa, or most of Asia. This is because the ferocity of its inhabitants allowed only fitful exploration of New Guinea until just the past several decades. Indeed, the large human populations in the Central Highlands were not even discovered until the 1930s, when aviation became used to explore the more remote parts of the island. Population growth rate is high in PNG, pressure to develop mines and log forests is accelerating, and the country is changing quickly. So, if there is any hope that the country’s rich complement of unique species is to persist beyond the next few decades, it is urgent that they be discovered and catalogued now. Doing this nicely joins my two main interests in science and conservation, and doing this in PNG, where undiscovered biodiversity is so great, ensures that boredom will not set in.

And, as one can surmise from the anecdote above, one is rarely bored in PNG. The country prides itself on the slogan “expect the unexpected”. Overlooking the impossibility of meeting this admonition, it nonetheless well captures the spirit of a place where events rarely unfold as planned. The country has a number of characteristics that make conducting fieldwork there challenging, and patience and adaptability are necessary to meet with success. Transportation infrastructure is generally poorly developed, the road network is small, and costs for travel and accommodation are correspondingly high. Typically, to work in a targeted area one must fly or take a boat to a relatively nearby village and then walk to the area of interest. These walks can vary in length from a few hours to several days. Ownership of land is traditional, meaning “communal”, and one must obtain permission from clan elders or chiefs in order to work in most areas. This is in addition to obtaining permission from the national and provincial governments. However, land ownership may often be disputed by two or more parties, and one can unwittingly become a pawn in local disputes if one serendipitously tries to work in one of those contested areas. Even when permission to work is granted, I’ve often met reluctance to allow us access to certain parts of the forest. These instances usually involve the more interesting, higher-elevation areas, which are often viewed as taboo or sacred and, hence, inspire a good deal of fear in the local inhabitants. Various explanations may be offered in turn for why we can’t access an area, with little concern apparent for the implied contradictions among the various reasons. Quiet persistence in pressing the issue typically results in eventual approval though, allowing access to the range of habitats necessary to sample an area’s fauna well.

Fieldwork in PNG can be treacherous for other reasons too. Like most tropical rainforests, New Guinea has a variety of threatening diseases, with malaria and tuberculosis being virtually ubiquitous and dengue fever and encephalitis occurring at lesser frequencies. But health concerns are not as severe as in many other tropical locations, such as Africa or parts of South America. In some areas, criminal activity in the form of robbery is common, making travel in those locations risky and leaving PNG with a reputation for being unsafe. In fact, most people in PNG are extremely friendly, notwithstanding the potential dangers posed by “rascals” (the local term for the criminals), and if one is admitted to work in a particular area, the responsible landowners and other villagers are typically careful to ensure that their guests come to no grief.

To meet my goal of finding undiscovered species of reptiles and amphibians I target for exploration isolated mountains or islands that have previously been unsurveyed for these animals. The likelihood of finding endemic species (those unique to only a small, circumscribed area and, therefore, less likely to already be known) increases with topographic isolation and as one gains in elevation, so a lot of my effort is focused toward reaching isolated peaks. I usually travel with a technical officer from the PNG National Museum (like Jimmy) or with one or another local friend from PNG; this facilitates discussions with local landowners and communications with local hired assistants. An expedition typically begins with us reaching a nearby village in which the landowners of the targeted area reside, explaining my research goals and activities to them, and getting their permission to work on their land. Permission is almost invariably granted, and the landowners are often concerned to know what might be unique to their area so that they may use the information to contest any disagreeable logging or mining ventures proposed for their lands. I then hire porters to carry our gear and food up the mountain, and assistants to work with us in camp, and off we go. Upon reaching a suitable elevation, we construct camp by clearing the understory of a small area of forest and using the cut poles to make our shelters, work station, loo, photo arena, etc. Depending on the height of the mountain, we usually set up two camps at different elevations so that we can sequentially sample as broad an array of the fauna as possible. Lowland species won’t be found high up the mountain (above, say, approximately 1000 m), and vice versa. The lower mountains may have two such elevationally stratified communities, but higher mountains can have up to four.

Once installed in camp, we then spend the next 10–14 days collecting the local herpetofauna, that is, the community of reptiles and amphibians. Frogs are most easily found by tracking calling males at night; lizards and snakes are obtained by walking the forest and examining likely shelters or looking for active animals. Several lizards that are otherwise hard to discover can be more readily obtained by emplacing short, temporary fences of plastic sheeting, along which buckets are sunk into the ground. Foraging lizards run into a fence, turn to walk along it looking for a place to cross, and drop into the buckets; we then collect them. I photograph and take tissue samples from representatives of each species, record the calls of the local frogs, and preserve most animals we capture, except for the most abundant species, which I release once we have obtained an adequate series. All samples and specimens are then returned to the Bishop Museum, Honolulu, where I study them, with duplicate samples later returned to the PNG National Museum so as to build an in-country reference collection.

Once back in the lab I pursue a variety of evolutionary studies on the specimens obtained: describing new species, taxonomically revising problematic genera or species groups, determining the evolutionary relationships among groups of interest, etc. My original expectation was that these surveys might lead to the discovery of perhaps a few dozen new species. However, that was a serious underestimate, and I have instead been laden with at least 150 new species of frogs, lizards, and snakes in my 14 expeditions to PNG. Consequently, most of my time back in the States has been devoted to the rather unglamorous task of merely describing and naming this large backlog, with less time than expected given to the more scientifically interesting studies examining evolutionary relationships or biogeographic patterns. This is the unanticipated peril of working in a poorly explored megadiverse country, and I have not even come close to sampling the country’s herpetofauna thoroughly. Consequently, I am confident that many additional species remain to be discovered.

Most of the newly discovered species are frogs because they are the least mobile of the three groups and tend, therefore, to become geographically isolated and develop narrowly endemic species more easily. Several of the frogs are the well-liked, colorful treefrogs that many people admire (Fig. 1), but a greater diversity consists of smaller, ground-dwelling frogs of usually drabber hue (Fig. 2). As well, a large number of lizards, and some snakes, are also new to science. Many of these species are not only new to science but have also proven to be unknown to the local inhabitants, who tend to be most aware of species that are edible, otherwise useful, or larger and more conspicuous. Tiny frogs and lizards, it turns out, are easily overlooked by almost everybody.

Island faunas are often described as “disharmonic”, meaning that they have only a limited sample of the entire range of lineages present on nearby continental areas. And although New Guinea is not as isolated as islands farther removed in the Pacific, it is still dominated by only a few lineages each of frogs, lizards, and snakes, even though species diversity is astronomical. So, for example, most of the hundreds of frog species occur in only two families. By way of comparison, nearby Borneo, of similar geographic size, contains eight frog families but far fewer species. Similarly, most lizards are either skinks or geckos, and most snakes also belong to only two families. So, species diversity in New Guinea is very high, but this has involved the relatively rapid radiation of only a few founding lineages, much as is seen in more remote islands.

For a person with the right sort of interests and temperament, this kind of exploratory research can be extremely rewarding. Biodiversity in the wet tropics is so high that novel scientific discoveries are virtually guaranteed. This involves not just the discovery of new species but also of unusual biological phenomena. Some of the biological oddities I’ve discovered are quite fascinating. For example, on a couple of isolated peaks in the southeastern extremity of PNG I found a new genus of frogs that turned out to be the smallest frogs on Earth (Fig. 3). Indeed, they include the smallest of all tetrapods (the group including amphibians, reptiles, birds, and mammals). To date, six species ranging in adult size from 7-11 mm are now known from this region. Their small size seems to have provided them access to new feeding opportunities in the small spaces among the leaf litter on the forest floor. It has also sharply curtailed their reproductive capacities, as females can carry only two mature eggs at one time; larger frogs may lay up to thousands of eggs at one time, although most produce fewer.

On one of the remote offshore islands of PNG I’ve also discovered a frog that has the most dramatic developmental change in color pattern of any known frog. Juveniles are glossy black and yellow, whereas adults are uniform peach or pink with a striking caerulean eye (Fig. 4). Coloration of the juveniles is reminiscent of that seen in the well-known poison-dart frogs of the Neotropics, suggesting that it may serve a similar warning function, and the juveniles also perch conspicuously exposed on vegetation during the daytime, which is an unusual behavior among frogs and is typically restricted to those having poisonous skin. Whether juveniles of this species are actually toxic to predators and display warning coloration still needs to be determined, as does clarifying why they would change their color pattern as they mature and lose such a presumed advantage.

A further oddity is provided by the frog Platymantis boulengeri, which is restricted to the large island of New Britain, to the east of New Guinea. In this frog, mature females average 40 times the body size of mature males (Fig. 5), giving them the greatest sexual size dimorphism of any tetrapods on Earth. It remains to be determined how reproduction is accomplished, given this dramatic size disparity, or what selective pressures would account for such a gross disparity in size.

Of considerable interest too is identifying species limits within what we term “species complexes” – groups of closely related species that have historically all been considered to represent but a single species. Elucidating biogeographic patterns in these groups helps us understand how rapid evolutionary radiations of animals and plants occur. As one example, I have shown that one gecko species previously thought to range widely across easternmost New Guinea, the Solomon Islands, and the rainforests of Queensland actually comprises six species in New Guinea and adjacent islands; other researchers have described five additional members of this complex in Queensland and the Solomons. Thus, a single “species” is shown to actually comprise eleven species. In another lizard complex currently masquerading under a single name (Fig. 6), I have collected ten species, some of which co-occur at the same localities. This group is especially interesting because in some of the species males and females look identical, whereas in others males are larger and more vividly colored than are females. On one island, two of these species occur together and are colored identically but differ dramatically in body size. New Guinea and its satellite islands are replete with similar complexes of previously unappreciated diversity, but most of these remain unstudied.

One of the major goals of this research program is to better understand the patterns of local regional endemism among the Papuan herpetofauna. New Guinea has a complex geological history involving the accretion of arcs of formerly offshore islands onto the northern margin of the Australian continental plate, and this has resulted in a large amount of rapid mountain building. As a consequence, a great number of the region’s reptiles and amphibians do not range across the entire island but are restricted to narrower regions of particular geological origin. For example, most of the species found in the southeastern peninsula of New Guinea do not occur in the Central Highlands, and vice versa. Similar results apply as well to the north-coast mountain ranges and the southern lowlands with respect to each other and to the first two areas. As a result, each of these regions has a distinctive herpetofauna that differs significantly from those of the other regions. Further, within any given region it is frequently the case that single isolated mountains, small mountain ranges, or offshore islands will have developed their own endemic species having even more restricted distributions. Sorting out these patterns of endemism is critical for setting efficient conservation priorities in the region because it is better to devote limited funding and effort to protecting regions harboring many local unique species than to regions with fewer.

So, one consequence of my surveys has been to identify important areas of local endemism for reptiles and amphibians that were previously unrecognized. As one example, prior to these expeditions, the seven major offshore islands of Milne Bay Province – the southeasternmost portion of PNG – were known to hold seven endemic species of frogs, four endemic lizards, and four endemic snakes. Now those numbers have increased to at least 40, 35, and 10, although the real numbers will almost certainly prove higher. Thus, an area formerly appearing to have modest regional endemism is now demonstrated to be of major importance within the Papuan region, and other researchers have shown this pattern to hold for plants too. When the smaller islands of the province have been investigated, the number of endemic species is likely to increase yet more. Similarly, on recent expeditions to the small range of peaks behind Tufi, Oro Province, I have identified more than one dozen new species that are likely found nowhere else because of inhospitable habitat isolating these peaks from the nearest uplands of the nearby Owen Stanley Range. The problem for biodiversity conservation is that a large number of these important areas of regional endemism exist in the region, and little work has been done to date in converting knowledge of these areas into practical on-the-ground conservation of forests. Given the traditional pattern of land ownership in PNG, it is obvious that such conservation can only effectively be done at the local level.

New Guinea is so relatively little explored that interesting discoveries need not be restricted to the group of organisms that I’ve chosen to research. For example, on one expedition a friend and I worked in an area having what must be one of the highest – though currently undocumented – waterfalls on Earth. Its remarkable height is easily viewed from a half a day’s walk distance, and could be viewed at even greater distance if intervening mountains did not block the view. The locals seem to take the view for granted, but to someone coming from outside, it provides a stunning surprise.

And this touches upon some of the other rewards that attend this sort of exploratory research. Much of New Guinea and associated islands consists of dramatic topography having magnificent beauty. Higher-elevation views can encompass large swaths of land that would take many days of hard travel to traverse. Similarly, exploration in these remote areas provides the opportunity to work in forests having little human disturbance, a rarity in much of the modern world. In the most remote areas humans are but infrequent visitors, the larger animals may consequently be rather tame, and the forest structure effectively pristine. The relevance of this condition for ecological research is obvious, but little of that has been done in New Guinea, in part because science is still so woefully behind in even cataloguing what lives on the island. Lastly, there is a sense of adventure gained from working in remote locations previously unvisited by Westerners. Aside from the thrill of being the first scientist to visit these areas, in some places one can make so many new discoveries that one gains some sense for what the famous 19th Century explorer biologists, like Alfred Wallace, must have experienced. For example, in one two-month expedition I discovered approximately 35 new species of reptiles and amphibians on a couple of remote islands, a feat I doubt I could ever hope to repeat, even in New Guinea. Such a density of new discoveries can be rarely met elsewhere in the modern world, and it is surprising that it can still be achieved at all.

These variously challenging but attractive features of field research in New Guinea may well change significantly in the next few decades. Already, cell phones have become ubiquitous in PNG in the past five years, removing some of the isolation of many of the places where I’ve worked, and making medical evacuation in the event of emergency more feasible in some locations. Increased boat traffic has also made some islands and coastal mountain ranges more readily accessible than they were just a few years ago. It may be that in another few decades the sort of adventurous field research that presently characterizes work in PNG will be reduced to the tamer variety that reigns across much of the rest of the world. In the meantime, however, much additional exploratory work remains to be done on the New Guinean fauna and flora, the region desperately needs researchers interested in meeting this need, but relatively few scientists seem interested. Nonetheless, it is very satisfying to work in remote locations little visited by outsiders, discover previously unknown facets of the earth’s biological inheritance, present them to the world, and say “behold!”.


Fig. 1. An array of newly discovered treefrogs, genus Litoria, from different localities in Papua New Guinea, shown against a backdrop of a mid-elevation waterfall. Some of these remain to be described.

Fig. 2. Eleven of 12 ground frogs of the genus Cophixalus newly discovered during my explorations, shown against a backdrop of dwarfed moss forest. I have named most of them in the past several years, but a few still require description.

Fig. 3. Four species of Paedophryne, the smallest adult tetrapods in the world. The species shown here vary from 8–10 mm in length.

Fig. 4. Oreophryne ezra, showing the striking change in color pattern that occurs as the frogs mature from smallest juveniles (A) to mature adults (F). So far as is known, no other frog exhibits such a dramatic change in color pattern as it ages.

Fig. 5. Platymantis boulengeri, a frog with the greatest disparity in body size between the sexes of any known tetrapod. Inset illustrates an average-sized mature female (left) and mature male (right).

Fig. 6. One example of a Papuan species complex: several species belonging to one complex of lizards currently masquerading under a single name as “Sphenomorphus aignanus”, shown against a backdrop of a high-elevation peak in the Owen Stanley Range. At least ten different species are involved in this group.

Fred Kraus
Fred Kraus

Fred Kraus is a research zoologist for the U.S. Department of Agriculture's National Wildlife Research Center, Fort Collins, Colorado, USA.  He was trained at the University of Michigan and has conducted field research at a variety of locations in the United States, southwestern Pacific, Caribbean, and South America.  His primary interest is in conducting scientific research that can be used to improve conservation of biodiversity, and his research focus is twofold: the reptiles and amphibians of New Guinea and associated islands, and invasive alien reptiles and amphibians.