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Observations on Cyclical Activity Patterns in Amphibians and Reptiles and a Request for Information

Wood FrogIn the course of my work with captive amphibians and reptiles I have often noted that the activity patterns of some seemed strictly controlled from within, while others were quite flexible.  This varied from species to species, and sometimes among individuals within the same species.

We know that most if not all species, ourselves included, are influenced by what might be described as an “internal clock”.  A number of processes, including daily activity patterns (termed circadian rhythms) are affected.  My own observations involved both daily and seasonal activities of a number of species.

Snapping TurtleAt one point I was caring for exhibits housing white-lipped treefrogs, Litoria infrafrenata and Wallace’s treefrogs, Rhacophorus nigropalmatus at the Bronx Zoo.  Both species are largely nocturnal.  On nights when zoo-sponsored special events resulted in the exhibit lights being kept on later than usual, each reacted differently.  The white-lipped treefrogs became active at 6 PM, the time when the lights would have been turned off on most days (as did, incidentally, the hoards of mice that occupied the building!).  The Wallace’s treefrogs, however, did not begin their evening activities until the lights were actually turned off, some 3-4 hours later than usual.

Similar examples abound – wild caught temperate species, such as Eastern painted turtles (Chrysemys picta) usually refuse to eat during the winter months, despite being kept warm.  However, the captive born offspring of such a turtle will generally feed throughout the year.

Wild-caught reptiles and amphibians hailing from temperate climates, such as the wood frog, fire salamander and snapping turtle viewed here, may become lethargic and go off feed in winter even if kept at their usually preferred temperatures.

Indian gharials (Gavialis gangeticus) under my care at the Bronx Zoo, hatched in their native northern India, refused to feed during their homeland’s cold season, despite having been shipped to NYC at less than 1 year of age.  The habit persisted for the 15 years or so that I was in contact with them.  Interestingly, they lost barely any weight during their 3 month long fast, even thought they were kept warm and remained active.


The abstract of an interesting article on temperature cycles in green iguanas is posted at:

Research Notes – Hourglass Treefrogs (Dendropsophus ebraccatum) can choose either land or water as egg deposition sites

Frogs are full of surprises when it comes to reproduction – there are species that incubate eggs below the skin of their backs and in the vocal sacs, while others carry them wrapped about their rear legs or construct foam nests on land.  But in May of this year Boston University biologists working in Panama uncovered what may well be the oddest reproductive strategy of all – a frog that actively chooses to lay its eggs on either land or in water, depending upon the threats presented by each habitat.  To date this is the only example of an egg that can hatch in either environment, and these frogs are the only vertebrates known to show such reproductive flexibility.

When breeding near shaded ponds, hourglass frogs lay their eggs on tree leaves overhanging the water (the tadpoles drop into the water upon hatching), thus avoiding fish and other aquatic predators.  However, when utilizing ponds exposed to the sun, the majority of the frogs lay their eggs directly in the water, lest they dry out before hatching.

The “decision” is not governed genetically, because the same female frog will choose different egg laying sites when placed in a shaded or un-shaded pond.

Amphibians were the first group of vertebrates to evolve some independence from water.  Biologists are now studying the hourglass frog to determine if its unique egg-laying flexibility might shed light on the evolution of terrestrial amphibian eggs.


You can read more about the hourglass treefrog and its relatives at:


Breaking Research – Newly Discovered Thread Snake (or Slender Blind Snake), Leptotyphops carlae, is the World’s Smallest Snake

A Similar Species, the Flowerpot SnakeAn article to be published later this month (Zootaxa; August, 2008) will announce that a newly described Thread Snake from the Caribbean island of Barbados is the smallest of the world’s 3,100+ snake species.  The Barbados Thread Snake grows to a mere 4 inches in length, is no thicker than a strand of spaghetti, and can coil comfortably atop a quarter.  It subsists largely upon ant and termite larvae, and may be threatened by habitat loss.  A relatively large hatchling – ½ of the adult size – emerges from the single egg laid by the female (perhaps there is no prey species tiny enough to support a larger brood of smaller-sized young).

A related snake, nearly as tiny, has been discovered on nearby St. Lucia.  Two snakes within the genus dwell in the southwestern USA – the other 103 species are found in Mexico, Central and South America, the Caribbean, Africa, India and Pakistan.

The Penn State biologist who discovered the snake, Blair Hedges, seems to have a quite a flair for his work – he and his colleagues have named 65 new amphibian and reptile species on Caribbean islands, including the world’s smallest lizard and smallest frog.

Islands and other isolated habitats are often home to the largest (Komodo Dragons, Aldabra and Galapagos Tortoises) and smallest animals within a group.  Islands are difficult for many animals to reach, so those that do arrive often evolve into a variety of forms (and, eventually, species) to fill the many empty niches (specialized roles within a habitat) – in fact, Darwin’s theory of evolution was sparked by his observations of this process among finches on the Galapagos Islands.  Caribbean Thread Snakes, Australia’s monitor lizards and the African Rift Lake cichlids are likely examples of this phenomenon.


You can read more about other species of Thread Snakes at:

Notes from the Field – An Aggressive Black Tegu Tupinambis teguixin (merianae)

While workBlack Teguing with Green Anacondas in the central Venezuela llanos (please see my article Hunting Anacondas in the Venezuelan Llanos) in the late 1990’s, I was delighted to find that Black Tegus, one of my favorite lizards, were quite common in the area.  Sometimes referred to as “New World monitor lizards”, it was indeed hard not to make that comparison when watching tegus hunting.  Active and intelligent, these stout lizards ate just about everything they came across – other lizards, snakes, turtle and bird eggs, small mammals, fish, frogs, crabs, large insects and carrion – and were major predators in this flooded grassland habitat.  I managed to catch a few young tegus, but old, battle-scarred individuals were impossible to approach, fleeing with amazing speed at the slightest move in their direction.

One morning I was scanning an area where I had seen a pair of Giant Anteaters a day earlier, hoping for another look, when my binoculars picked up a co-worker doing what appeared to be an odd dance of sorts.  Upon closed inspection, I saw that he was repeatedly jumping back from a yard-long black animal that was hurling itself at his leg.

I ran over and found him in a pitched battle with a large male Black Tegu.  The animal was not cornered and had ample opportunity to turn and run, as they invariably do, but simply refused.  Nest-guarding has been reported in some populations, but among females only and there was no nest to be found here.  Upon subduing the ornery fellow I found that he was uninjured, and capable of moving normally.

The only explanation that seemed to make any sense (outside of a bad temper!) was that he had not warmed sufficiently for a fast burst of speed (it was morning, and the lizard was in grass flooded by cool water).  However, he seemed to be exerting as much energy fighting as he would have by running!  Upon being released, he continued to hold his ground until we relinquished what was obviously a prized piece of real estate.

Of course, there are general rules as to typical species’ behaviors, but reptiles and amphibians show quite a variance in “personality traits” – this may assist them in adapting to changing environmental conditions and to captivity.  .

An interesting article on Black Tegus and related species is posted at:

Tortoise Observations – Feisty Terrier No Match for African Spurred (Spur –Thighed) Tortoise, Geochelone sulcata


Sulcata TortoiseThe responsive ways of North Africa’s massive Spurred Tortoise are well known to private and professional turtle keepers.  Inquisitive and alert, these arid country natives are quick to become possessive of their territories and, sometimes, owners.  They adjust rapidly to changes in their environments – two 80 pounders that I kept in a half-acre outdoor exhibit at NYC’s Prospect Park Zoo never ceased to amaze me, despite having been under my daily observation for years.


A few years ago, my mother kept an abandoned 30-pound male free-ranging in her yard until a suitable home could be found for him.  He was adopted by a friend, and in short order took over his yard – digging furiously to get at the dog next store, bullying the owner’s dog and ramming or ignoring anyone save his owner.  He never failed to appear when his owner came home, and walked over to sit near him at every opportunity.


In June of this year, a neighbor’s terrier-mix (an annoying, yappy beast, I might add!) got into the tortoise’s yard and, in true terrier fashion, made right for what looked like an easy target.  He managed to bite the tortoise’s front leg – at which point the leg was withdrawn into the shell.  As you may know, Spurred Tortoises have thickly-scaled limbs and immense strength, and use their legs as a shield against predators.  Evolving in a habitat with much larger and fiercer predators that a mere terrier, the tortoise easily pinned the animal between its massive foreleg and shell, and there it remained.


Efforts by several strong men failed to straighten the tortoise’s leg and, in fact, seemed to strengthen his resolve.  Water was poured on the animals, also to no avail.  I was unable to get to the scene, and thought an injection of a muscle-relaxer might be required.  However, I first suggested that the animals, being carefully supported, be submerged in a child’s wading pool.  Thankfully, this did the trick and the tortoise released his wrestler’s “scissor lock”.


Despite having been gnawed on for over an hour, the tortoise’s leg was unmarked.  The terrier, I must say, seemed eager to do battle once again as soon as he cleared the water from his nose – but his owner had more sense!



You can read about the natural history of the African Spurred Tortoise at:



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