Home | Field studies and notes (page 30)

Category Archives: Field studies and notes

Feed Subscription

The Marine Toad, Bufo marinus (recently re-classified as Rhinella marina) in Nature and Captivity – Part I, Natural History

Recently I wrote about those tiny jewels of the frog world, Latin America’s poison frogs (Article Part I and II).  Today I’ll introduce you to a behemoth that is largely their direct opposite, the massive Marine Toad – at once one of the world’s most interesting and troublesome of amphibians (actually, the people who have transported it around the globe are troublesome, not the toads!).

Physical Description
This largest of the world’s toads may reach 10 inches in length.  Generally brown to tan in color, some individuals show a yellow or reddish tint.  One that I received from a friend working on Guam was clad in several shades of yellow and quite beautiful. Enormous paratoid (poison) glands extend from behind the eyes to the sides of the body.  The body is squat and rounded in profile.

There seems to be a great deal of variation in size among different Marine Toad populations, with the true giants that came out of Colombia and Suriname in the 1960’s and early 70’s being rarely seen in the trade today.  I examined a great many in working in Venezuela, and most were in the 4-6 inch range (this comports with locally published accounts).  Florida’s introduced animals are relatively small in size (but large as toads go), as are those in south Texas.

Me with Large Marine ToadThe photo accompanying this article shows me holding a large female that was collected, I believe, in Colombia.  She has inflated her lungs with air to prevent my swallowing her (fat chance!) – the stick is to discourage the two 18 foot long anacondas that share her exhibit from attempting to swallow me!

Range and Habitat
People are sometimes surprised to learn that the Marine Toad is a US native, but those living in southern Texas are indeed part of a naturally occurring group.  Florida and Hawaii’s large populations are introduced.

From Texas, this toad range south from southern Sonora, Mexico through Central America to central Brazil, Amazonian Peru and Bolivia.  Marine Toads have been widely introduced and are well established in Florida, Hawaii, Taiwan, Japan, New Guinea, Australia, and throughout the islands of the Caribbean (i.e. Puerto Rico, Antilles, St. Lucia) and the South Pacific (i.e. Fiji, Guam).

Marine toads dwell in a wide variety of habitats, including open forest, overgrown scrub, grasslands, fields and marshes.  They adjust well to disturbed sites and are common in agricultural areas, suburbs and urban parks (i.e. within Miami, Fla.).  Several I observed on Tortuguero, Costa Rica, crossed a 30 foot stretch of mowed lawn each evening to feed near my bedroom’s outdoor light.

Status in the Wild
Generally common within natural range and usually very common, to the point of being a harmful invasive, where introduced.

Marine Toads consume nearly any creature that fits within their cavernous mouths – centipedes, roaches, beetles, millipedes, earthworms, land crabs, spiders and other invertebrates, frogs, lizards and snakes.  Mice, birds and similar creatures are taken when encountered, but stomach analysis of toads in the Venezuelan llanos (grasslands) showed this to be a rare occurrence in that habitat.

This is one of only a very few frog species to consume non-living food items (African Clawed Frogs, Xenopus spp. will take carrion and, amazingly, Izecksohn’s Treefrog of Brazil eats berries).  While in Costa Rica, I regularly observed a large toad eating dog food (after pushing open a screen door to get at it!), and those kept by co-workers at the Bronx Zoo ate salad set out for tortoises.  Field reports from New Guinea indicate that Marine Toads there rely upon vegetation as food during the dry season.  Stomach analysis of wild individuals indicates that they also will take carrion (chicken and fish) and the eggs of other Marine Toads.

In addition to hunting by sight, these toads apparently utilize olfaction (rare for a terrestrial frog) as well.

Marine ToadAn extremely flexible reproductive biology accounts for this animal’s success as an invasive species.  Unlike most amphibians, it can reproduce throughout the year in favorable habitats, in brackish (saline) water and in waters containing high fish populations.

Large females may lay as many as 36,000 eggs, attached in strings to aquatic vegetation.  In contrast to most frogs, both eggs and tadpoles are protected by virulent toxins.  The tadpoles take 10 days to 6 months to transform, depending upon temperature and diet, and can survive 10 hours without water.  They consume algae, dead plants, carrion and each other, and generally out-compete or eat the tadpoles of other species.  Newly transformed toads disperse widely and often establish new limits to existing ranges.

Marine toads are likely the world’s most widely introduced amphibian (American Bullfrogs and Greenhouse Frogs are close competitors for this title).  They are generally transported to agricultural areas to control insect pests, a strategy that rarely works.  In Australia, for example, the toads seldom catch cane beetles, their intended prey – the beetles dwell high above the ground and the toads do not climb.

Introduced populations expand rapidly, consume native animals and out-compete others.  On Oahu, Hawaii, 148 introduced toads multiplied to over 100,000 in a 2 year period.

The Marine Toad’s toxins are powerful and complex.  Threatened toads will lower their heads and attempt to bring the poison-containing paratoid glands in contact with the attacker.  In Australia, 3 species of quoll (a medium-sized mammal) and 8 species of monitor lizards prey upon the toads and are declining due to deaths caused by the toad’s skin toxins.  Dingoes, snakes, foxes, dogs and other animals have also expired after eating Marine Toads.

Most predators occurring within the Marine Toad’s natural range leave them strictly alone.  I have, for example, housed them with green anacondas for many years – despite that fact that the snakes will avidly consume other frog species.  However, several snake and possibly bird species have evolved toxin immunities and prey upon them.  In Australia, White-Tailed Water Rats have apparently learned to avoid the skin toxins by flipping the toads and chewing through the belly skin to reach the internal organs.

Marine toads are quite responsive to their surroundings.  Captive animals anticipate food upon seeing their keepers, and those living in developed areas learn to gather under street lights to capture insects.

A field report detailing some of the unusual foods and other items found in the stomachs’ of free-living Marine Toads is posted at:


Has Anyone Observed This?….. Madagascar and Standing’s Day Geckos (Phelsuma madagascariensis grandis, P. m. madagascariensis, P. standingi) maintain excellent health and reproduce without a UVB source

It is well known that many species of lizard, turtle and crocodilian require ultraviolet light of a specific wavelength (290-310 nanometers) in order to synthesize Vitamin D3.  This vitamin, in turn, allows the reptiles to make use of the calcium in their diets.  Such reptiles (which generally bask in the sun in the wild) develop calcium deficiencies and a host of related problems if denied UVB in captivity.  This occurs despite their being offered a diet high in calcium.

Day geckos of the genus Phelsuma seem to require quite high levels of UVB in captivity.  Several species, and gravid females in particular, develop bulging “chalk sacs” (calcium stores) behind the head, and are quick to succumb to health problems in the absence of UVB.

Some years ago, however, I observed a situation that caused me to question what I knew, or thougMadagascar Giant Day Geckoht I knew, about this subject.  A number of Madagascar, Madagascar Giant and Standing’s Day Geckos were released into a densely-planted indoor “rainforest” in NYC’s Central Park Zoo.  The lizards thrived and reproduced, and, when last I checked, had been doing so for several generations.  Animals that are captured from time to time exhibit excellent bone density and overall good health, despite the fact that they have no access to natural or artificial UVB.

The aviary in which they live supports a wide variety of spiders, beetles, roaches, sow bugs and other invertebrates, as well as nectar and fruit producing plants.  I imagine that the lizards, amid this banquet, have found a source of calcium that is usable in the absence of UVB, or D3 that can be absorbed from the diet.  I will keep you posted as to further developments.

I have since spoken with lizard-keepers who maintain day geckos without UVB.  However, as we know little of the interaction between calcium, phosphorus and Vitamin D3 in these animals, a good deal of experimentation is needed, and the results are spotty.  The lizards at the Central Park Zoo are the most robust I’ve seen, and the population has remained so for 15 years or more at this point.

Red-eared Sliders, Chrysemys picta elegans, also suffer from calcium deficiencies if unable to bask under a UVB source – yet I know of a number of instances in which perfectly formed specimens were raised without such.  Again, I can only guess as to the explanation.

I tend to encourage dietary variety in my nutrition articles, due in part to experiences such as described above.  We really know very little about many common reptiles and amphibians, especially concerning nutrition.  I would greatly appreciate hearing about experiences you may have had – good or bad – regarding UVB light and diet.

The abstract of an article about Zoo Zurich’s “free-ranging” colony of Madagascar Giant Day Geckos is posted at:


The Natural History and Captive Care of the Frilled Dragon or Frillneck Lizard, Chlamydosaurus kingii – Part I, Frilled Dragons in the Wild

The frilled dragon was a creature of legend to budding American herpetologiFrilled Dragonsts growing up in the 60’s and 70’s – we devoured what little published information existed, but seeing one alive was out of the question, short of a trip to its habitat.  It is still hard for me to imagine that, as a Bronx Zoo reptile keeper, I acquired my first 2 individuals a mere 15 or so years ago (at $1,500 each!).  Today these magnificent lizards are commercially bred in large numbers – both on “farms” in Indonesia and by herptoculturists worldwide.

Although not an “easy” species, and certainly one requiring a good deal of space, frilled dragons are among the most rewarding lizards to keep, and will provide you with a lifetime of interest and enjoyment.  This week we’ll take a look at their natural history, so that we can better understand how to provide for these fascinating animals in captivity.

Physical Description
The body color ranges from grayish through orange-brown to nearly black, often with dark variegations along the sides, and usually matches the color of local tree trunks.  The inner surface of the frill (the large skin fold about the neck) is shaded in yellow, black, orange and/or red.  The hind legs are powerfully built.  Males can reach 38 inches in length; females are somewhat smaller.

The neck frill is supported by cartilaginous rods and is connected to muscles in the tongue and jaw.  It expands when the lizard gapes its jaws and is used to intimidate predators and rivals, and in courtship displays.  Frilled dragons are one of the few lizards to use bipedal locomotion – they flee predators by rising up and running off on their rear legs.

Range and Habitat
Frilled dragons are found in northern Australia and southern New Guinea.  They frequent open tropical and warm temperate forest and wooded scrub land.

Largely arboreal, they dwell in the forest canopy during the dry season.  During this period the lizards reduce their food and water consumption, metabolic rate and body temperature.  The rainy season is largely spent on tree trunks within 4-15 feet of the ground.

In northern Australia and other parts of the range, frilled lizard habitat is subjected to frequent fires (natural and human induced, as a component of habitat management) during the dry season.  Field research has revealed that the lizards escape the fires by re-locating to the highest branches of large Eucalyptus trees.  Interestingly, it was also found that a number of individuals descend to the ground and shelter in abandoned termite nests during fires – a most unusual (and, it would seem, learned) behavior for an arboreal lizard.

Status in the Wild
Populations appear stable; protected by the Australian government.

Caterpillars, scorpions, ants, termites, beetles, spiders and other invertebrates, small lizards and snakes; nestling birds and small mammals are taken on rare occasions.

Frilled dragons seem to occupy a unique feeding niche within a lizard-rich habitat.  Although largely arboreal, they feed on the ground by dropping from their tree-trunk perches to intercept passing insects and small animals.

Research has shown that, immediately after dry season fires, the percentage of large invertebrates in the frilled dragons’ diets increases significantly.  It seems that the lizards are able to see larger prey animals more easily once the ground cover has been burned off.  So strong is this effect that lizards living in unburned areas move into the burned areas as soon as the fires have subsided.

Males are highly territorial and fight for breeding rights.  Both sexes use neck frill displays during courtship and territorial disputes.  Mating coincides with the start of the rainy season.  Females bury 8-14 eggs in the ground, and may produce 2 clutches each year if food is plentiful.  The eggs hatch in approximately 69 days and the young average 2 inches in length.  Hatchlings stay in close proximity to each other, possibly as a defense mechanism, for approximately 10 days.

Frilled Dragon Relatives
Frilled dragons are classified within the family Agamidae, which contains over 300 species.  Some of its members are among the most common and typical lizards of their habitats, while others have extremely specialized diets, unique adaptations and very restricted ranges.  Most hunt beetles, spiders, scorpions and a wide variety of other invertebrates, but the dabb lizards, Uromastyx spp., of  North Africa and the Middle East are herbivorous (in captivity they are especially fond of dried split peas!) while Australia’s thorny devil, Moloch horridus, subsists entirely upon ants.

The toad-headed lizards, Phrynocephalus spp. and the pygmy lizards, Cophotis spp. are unique among the Agamids in bearing live young.  Toad-headed lizards inhabit the deserts of south and central Asia, and utilize microscopic channels among their scales to funnel dew to the mouth.  Southeast Asia’s slow-moving pygmy lizards, likened by some to chameleons, have prehensile tails and dwell in high-altitude moss forests.

Perhaps the most commonly-seen of Africa’s lizards are various species of the genus Agama (commonly known as “agamas”), males of which perch on fences and houses and bob their brightly-colored (often blue) heads in courtship displays.  As with most Agamids, their head and body coloration intensifies during the breeding season.   Equally conspicuous throughout much of India and Southeast Asia are the various Calotes species, often locally referred to as “garden lizards” due to their propensity to take up residence near people.  Australia’s bearded dragon, Pagona vitticeps, is a popular pet, with millions bred yearly by hobbyists to supply the trade.

Among the more unusual Agamids are the 40 or so species of Draco, the “flying lizards”.  These supremely adapted aerialists are the only lizards to have developed elongated ribs to assist in gliding (flying geckos, Ptychozoon spp., also glide, but utilize small skin flaps along their sides).  The flying lizard’s ribs are covered by loose-fitting, brightly colored skin (the patagium) that, when extended, allows for “flights” of at least 50 feet and for considerable in-air maneuverability.  Other unique family members include the cold-tolerant Himalayan agama, A. himalayana, which ranges to 11,000 feet above sea level, and the horned agamas, Ceratophora spp., males of which sport a long, flexible appendage on the tip of their snouts.

We still have a lot to learn about the spectacular frilled dragons – please observe yours closely, and pass along your ideas and questions.  I’ll be sure to include them in future articles.

Excellent summaries of two frilled dragon field studies are posted at:

Herp Notes – Seagoing Frogs, Parthenogenic Snakes, and a Request for Your Observations

While working in a large tropical bird exhibit at the Bronx Zoo some years back, I was startled to come across tiny frogs hidden among the leaf litter.  I was able to identify them as Greenhouse frogs, Eleutherodactylus planirostris (an apt name, it turns out).  These 1.4 inch-long Cuban natives have been transported around the world, hidden among plants and soil.  Their eggs are laid on land, and the tadpole stage is passed within the egg, so the frogs readily establish themselves in greenhouses and other warm, humid habitats.  It always pays to (discretely) poke around in walk-through zoo exhibits and such places – you never know.


The greenhouse frog belongs to the family Eleutherodactylidea, which contains over 800 species.  Recent research at Pennsylvania State University revealed that all types currently found in Mexico, Central America and the Caribbean arrived there by rafting on vegetation over the open seas from South America, rather than across an ancient land bridge, as was previously assumed.  Apparently, individuals of a single species landed in Mexico, and others (again, 1 species) in Central America, and then each evolved into the large number of species found in these places today.


Another world traveler, the Flowerpot snake (or Brahminy blind snake), Ramphotphlops braminus, also utilizes a unique reproductive strategy to establish new populations in far-flung habitats.  All individuals of this species are female and reproduce via parthenogenesis, so only 1 animal is needed to start a colony.  I’ve had the good Flowerpot Snakefortune of running into this odd creature, as well as “banana” spiders, rattlesnakes and others, in unexpected surroundings – more on that next time.



An informative article on this frog’s history in Florida, along with a photo, is posted at:



Hunting Anacondas in the Venezuelan Llanos – notes and photos for fans of giant snakes

Growing up near the Bronx Zoo, I became fascinated by giant snakes early on, as these magnificent creatures were always featured prominently in my favorite building, the Reptile House.  So it was with great anticipation that, after some years as a reptile keeper for the zoo, I set off for Venezuela to assist in field studies of the green anaconda, arguably the world’s largest snake.


Accounts of what I observed and learned during three visits to that country’s central llanos area (seasonally flooded grasslands) would fill several books.  I would like here to just give you some facts and photos – in the future, I will highlight some of my experiences in longer articles.


Despite long-standing legends to the contrary, (and, recently, a plethora of internet photos) there is only one reasonably reliable account of a snake measuring over 30 feet in length (I’ll cover the details of this and related stories in the future).  In fact, the Bronx Zoo offered a cash reward, established, as legend has it, by Theodore Roosevelt, for a living snake in excess of 30 feet.  That reward, now withdrawn, stood uncollected for nearly 100 years (I was involved in the last attempt to collect it – please look for details in the future).


The snake you see pictured here was the largest that I and my colleagues encountered.  It measured just over 17 feet long and weighed 215 pounds.  As you can see from the close-up of my hand on its head, she (all anacondas Me with 17 ft, 215 lb. green anaconda
of this size are females) put up a quite vigorous battle when captured – indeed, one of her teeth remains imbedded in my wrist till this day as a reminder!  A number of the 500+ green anacondas that were marked during the study were in the 15 to 16 foot range.


I was fortunate to come upon quite a few anacondas in the process of feeding upon a wide array of animals, including capybara, caiman, jacanas and other birds, turtles and, most unforgettably, a deer of 60 pounds in weight.  Please look for future articles on the details of these most fascinating encounters.


The Venezuelan llanos, especially in the dry season, offers a wildlife-viewing extravaganza that is difficult to put into words.  Encounters with crab-eating foxes, freshwater dolphins, giant anteaters, armadillos, electric eels, caiman, scarlet ibis and countless other creatures large and small are all but guaranteed.  Cougars, jaguars, giant otters, tamandua, tree boas, tegus and a host of others are also a real possibility.  I am planning to write an article for people who might like it explore (and “exploration” it is, in the true sense of the word) this area – please look for it in the future.

 Anaconda Emerging from the water


You can learn more about the field research project I described in this article at:

Anaconda Expert Wades Barefoot in Venzuela’s Swamps

Scroll To Top