The Natural History and Captive Care of the Mexican Axolotl, Ambystoma mexicanum: Natural History – Part 1

Hello, Frank Indiviglio here.

AxolotlRelatively scarce in the pet trade when I first began in the field (admittedly quite awhile ago!), interest in the Mexican axolotl has exploded in recent years, and today it is arguably the most commonly-kept salamander in the USA. Its popularity has soared in other countries as well, and oddly enough, it has become somewhat of a pop culture figure in Japan.

The Mexican axolotl has the rare distinction of being simultaneously one of the world’s most highly endangered amphibians (in the wild) and a common pet and laboratory subject.

Please note: the aquatic larvae of all species of salamanders are termed “axolotls” in some references, i.e. as in “tiger salamander axolotls”. The name as used here refers to young and adult Ambystoma mexicanum only.

Classification
Class: Amphibia
Order: Caudata
Family: Ambystomatidae

A complex of a dozen or more related aquatic salamanders dwell in mountainous lakes in the vicinity of this species’ range. The waters inhabited by one of these, the Lake Patzucuaro salamander (A. dumrelii), are high in dissolved salts. Perhaps as an adaptation to its brackish environment, this salamander sheds its outer skin layer continuously throughout its life.

The family Ambystomatidae, limited to North America, contains approximately 40 terrestrial and aquatic members, including such well known species as the tiger salamander (A. tigrinum), marbled salamander (A. opacum), spotted salamander (A. maculatum) and Pacific giant salamander (Dicamptodon ensatus).

Physical Description
The Mexican axolotl is stoutly built and reaches 9-12 inches in length. The head bears large, bushy red gills and the laterally compressed tail is equipped with a swimming fin. Wild specimens are dark brown in color; albino, leucistic, black and piebald strains are common in laboratories and the pet trade.

Range
This species’ entire natural range is limited to an area of 6.2 square miles in size. It is native only to Lakes Chalco and Xochimilco, adjacent to the southern edge of Mexico City, in central Mexico.

It appears now to survive only in a small fragment of that tiny habitat – the southern remnants of Lake Xochimilco, and perhaps within associated canals and private garden ponds.

Habitat
The Mexican axolotl is entirely aquatic. The high-altitude lakes it inhabits are deep, heavily-vegetated, mud-bottomed and cool in temperature. Axolotls can extract oxygen from air or water, utilizing gills, lungs and skin.

Status in the Wild
This salamander is extremely rare in the wild, and is considered to be among the world’s most endangered amphibians. Recent surveys in its tiny natural range have turned up only 0-42 specimens, despite 1,800 net casts.

Lake Chalco has been largely drained, and no axolotls survive there. Lake Xochimilco has been severely polluted and impacted by flood control measures, and is extensively channelized to accommodate “floating gardens” of flowers and vegetables.

Protected by the Mexican government and listed on Appendix 2 of CITES, Mexican axolotls are none-the-less still collected for the food and medicinal trade, and are also threatened by large populations of introduced fish (Tilapia and carp).

Click: The Natural History and Captive Care of the Mexican Axolotl: Part 2, To read the 2nd half of this article.

Frank

The Green Treefrog, Hyla cinerea: Notes on my Collection

Green TreefrogsHello, Frank Indiviglio here. Recently I posted an article about native treefrogs in my own collection: My Animal Collection: How a Herpetologist Keeps Barking Treefrogs (Hyla gratiosa) and Gray Treefrogs (Hyla versicolor). Today I’d like to add some thoughts on another US native, the very attractive green treefrog. Please see my earlier article for detailed information on treefrog care.The green treefrog is so often collected for the pet trade, and so inexpensive, that many here take it for granted. It is, however, one of the most beautifully colored of the word’s Hylids, and much favored by hobbyists in other countries.

Feeding Tips
Green treefrogs top out at 2 ½ inches in length, and are slender in build. I’ve found that they do best when given only small insects, the size of a ¼ to ½ inch cricket, despite their willingness to tackle larger prey. I suggest that you avoid adult crickets, large waxworms and the like, as they may be too much for this species’ digestive system to handle on a regular basis.

Perhaps due to their arboreal nature, these frogs react very strongly to flying insects. The feeding response is quite dramatic when I offer them moths and small flies, and noticeably different than their reaction to crickets and waxworms. Small wild-caught insects (Zoo Med’s Bug Napper is an excellent trap) should be given regularly. Most green treefrogs feed readily from plastic tongs….canned silkworms are an excellent addition to the diet. These frogs are persistently arboreal, so burrowing insects such as small butterworms and waxworms should be placed in cups suspended from tree branches, or hand-fed.

Green treefrogs are accomplished jumpers, and adept at snatching insects on the wing. At feeding time, a group I housed in the Bronx Zoo regularly stole the show from their somewhat sedentary exhibit mates – a pair of water moccasins!

Captive Breeding
Unfortunately, little attention is given to breeding this spectacular frog in captivity. Males in the zoo group I mentioned began calling in response to increased showers, but the females did not respond with eggs. As most green treefrogs in the trade hail from Florida and Louisiana, a dry period followed by frequent misting and a rise in temperature of 5-10 F might do the trick.

Please write in with your questions and comments. Thanks, until next time, Frank Indiviglio.

You can learn more about the natural history of the green treefrog at:
http://www.natureserve.org/explorer/servlet/NatureServe?searchName=Hyla+cinerea

The Yellow-Spotted Sideneck Turtle , Podocnemis unifilis, in the Wild and Captivity: Natural History – Part 2

Click: The Yellow-Spotted Sideneck Turtle , Podocnemis unifilis, in the Wild and Captivity: Natural History – Part 1, to read the first part of this article. 

 Diet

Adults are mainly herbivorous and subsist largely upon aquatic vegetation and fallen fruits, but will also consume insects, fish, carrion, snails and crayfish (the preferred diet of juveniles). 

The yellow-spotted sideneck sometimes utilizes a feeding method known as neustophagia to filter particulate food matter from the water’s surface.  The turtle opens its jaws at the surface and rapidly pumps the throat, which has the effect of drawing in only the thin surface film.  A rapid snap of the jaw expels the ingested water and retains the organic matter.  Neustophagia enables a relatively large turtle to obtain significant nutrition from a food source that would be otherwise too small to exploit.

This and related turtles sometimes gather in large numbers below trees overhanging water when fruits ripen and fall (please see below). 

Reproduction

The mating season varies throughout the range.  As in many aquatic turtles, males court females by stroking their heads with the claws of the forelegs. 

Females often nest communally, digging nest holes in sand or, on occasion, in mats of floating vegetation.  Several clutches may be produced each season, with 6-52 (average 19) eggs being laid at once.  The hatchlings average 1.6 inches in length, and emerge after 60-75 days. 

Encounters in the Field

While engaged in field work with green anacondas, I was fortunate to find myself in the Venezuelan llanos… prime habitat of the savanna sideneck turtle, Podocnemis vogli, a close relative of the yellow-spotted sideneckOn one memorable occasion, I came upon thousands of these shy yet inquisitive turtles at a river oxbow, below a stand of fruit trees. 

Droves appeared at the surface, briefly looked at the boat and dove, to be replaced by an equal number of turtles a few seconds later.  Upon entering the water, I was astonished to find that the entire pool was packed, top to bottom, with turtles…to move, I literally had to push my way through a nearly solid mass of shells.  Being in the center of so many frantically swimming turtles was quite unlike anything I had experienced, either before or since.

Notes on Related Turtles

Podocnemis erythrocephala

The red-headed sideneck turtle, P. erythrocephala, is a much sought after species that rarely if ever enters the pet trade anymore.  Unlike many turtles, males retain the brilliant red head markings that characterize hatchlings.  Limited to the Rio Negro and Rio Casiquiare drainages in Venezuela and Brazil, it is a secretive species that mainly keeps to blackwater areas.

This turtle’s wild status has not been well-studied, but it is assumed threatened by past over-collection and habitat loss.  Those I have worked with proved to be fairly shy, even after nearly 3 decades in captivity. They did not rush towards me at feeding time, as would almost any other turtle after such a time period, and reproduced only sporadically.  We certainly need to learn more about the keys to the captive breeding of this species.

Podocnemis expansa

The giant South American river turtle (P. expansa) is the heavyweight of the family and, at 3 feet in length, one of the world’s largest freshwater turtles.  Inhabiting tributaries of the upper Amazon and rivers in the Caribbean drainages of Guyana and Venezuela, it favors deep water.  Females have the unfortunate habit of gathering in huge numbers along favored nesting sites at predictable times each year.  This renders both they and their eggs quite easy to collect, and the species is now in dire trouble throughout much of its range.

During my years at the Bronx Zoo, I cared for a breeding group of these impressive turtles, some of which approached 40 years as captives, and were likely 60-70 years old.  Several times I was called to Kennedy Airport to identify turtle eggs found in luggage (and, in one case, filling 2 shopping bags!).  Twice I was tempted to identify seized eggs as belonging to a sea turtle, but upon close examination and some research into the collection site found them rather to be eggs of this massive species.

On to captive care next time…until then, please write in with your questions and comments.  Thank you, Frank Indiviglio.

A great deal of information concerning the harvesting and conservation of this and other South American turtles and tortoises is posted at:

http://www.fao.org/docrep/T0750E/t0750e09.htm

Image referenced from Wikipedia.

The Yellow-Spotted Sideneck Turtle , Podocnemis unifilis, in the Wild and Captivity: Natural History – Part 1

The Yellow-Spotted Sideneck Turtle (Terecay, Yellow-Spotted Amazon River Turtle), Podocnemis unifilis, and several relatives were popular pets in the 1970’s, but soon became unavailable due to over-collection (largely for the food trade) and the resulting limitations on importations.  Australian sidenecks soon filled the void, and remain in the spotlight today. 

However, captive breeding efforts are beginning to show some promise, and the yellow-spotted and other South American species are poised, it seems, to re-enter the per trade.  These sizable turtles are not for everyone, but we need to learn more about them…hobbyists with some experience and space might help greatly in that regard.  Hopefully the following information will help you to decide.

Classification

Sideneck turtles are classified in the Testudine sub-order Pleurodira, while all other turtles are placed in the sub-order Cryptodira.  Approximately 75 species of sideneck turtles are found in Australia (where they form the vast majority of the aquatic turtle fauna), South America east of the Andes, sub-Saharan Africa and Madagascar.

The vast majority of the world’s turtles draw their heads straight back into the shell, largely concealing it within. Sideneck turtles retract their heads on an angle, so that the head is pointing sideways when withdrawn, and both it and the neck remain partially exposed.   This limits the protective value of the shell, and may explain why there are no terrestrial sideneck turtles (mammalian predators would easily prey upon them) and why, outside of Australia, they have been largely out-competed by typical aquatic turtles.

Physical Description

The domed carapace (upper shell) averages 12 inches in length, although particularly large females can attain 18 inches.  The shell is attractively colored in muted olive, gray or brown, and bright yellow-orange spots mark the head.  These fade with age but often remain discernable through adulthood.

Males are the smaller sex and have spotted heads with greenish eyes while females have plain, buff-colored heads and black eyes.

Range

This turtle inhabits northern and central South America, including the Caribbean drainages of Guyana, French Guiana, Venezuela and Columbia.  It also occurs in the upper tributaries of the Amazon River in Columbia, southern Venezuela, eastern Ecuador, northeastern Peru, northern Bolivia and Brazil.  There are unconfirmed reports of small populations in Trinidad and Tobago.

Habitat

Yellow-spotted sidenecks favor quiet, slow-moving waters such as ponds, lakes, swamps, flooded llanos (grasslands), oxbows and the backwaters of larger rivers.

Status in the Wild

This species’ status is largely unknown, but it is collected in many areas for food.   It is listed on Appendix II of CITES and designated as “Vulnerable” by the IUCN.

Click: The Yellow-Spotted Sideneck Turtle , Podocnemis unifilis, in the Wild and Captivity: Natural History – Part 2, to read the second part of this article.

Image referenced from Wikipedia.

Until than,

Frank Indiviglio

Albino and Leucistic American Bullfrogs, Rana catesbeiana (Lithobates catesbeianus): a Request for Your Input

Hello, Frank Indiviglio here.

Albino BullfrogsAlbino and leucistic American bullfrogs are becoming quite popular in the pet trade.  The two females that I’m holding in the accompanying photograph are approximately 1 year old, and were received as tadpoles.  The other photograph shows two others in an exhibit I prepared for the Maritime Aquarium in Connecticut (note the pumpkinseed sunfish…bullfrogs usually do quite well with predatory fish).  

Basking Platforms

Albino Bullfrogs in ExhibitThe frogs in the exhibit photo are resting upon an R-Zilla Basking Platform.  I use these extensively, both at home and in the zoo/aquarium exhibits that I design.  The platforms are very realistic in appearance, especially when surrounded by real or artificial plants and with a light covering of algae.  They are equipped with a stick built into the surface – you can wedge a bit of R-Zilla Beaked Moss below this for extra effect.  I also favor the Zoo Med Turtle Dock.  One end of this platform slopes below the water, providing easy access to metamorphosing frogs, newts and other creatures that might need a bit of help exiting the water.  I’ve also used this model for a spotted turtle that lost his rear legs in an accident…the gentle slope allows him to easily climb on board.

In most situations, I prefer suspended platforms to rock piles, as the former leave the water below clear for swimming.  Cork Bark works well also, but floats freely or must be cut to fit the tank and wedged into place.

An Un-cooked Chicken!

Most visitors to the aquarium remark favorably upon the albinos, which live in an exhibit with normally colored bullfrogs.  I did, however, overhear one gentleman respond to his companion’s “Aren’t they interesting?” with a definitive “They look like un-cooked chickens”!

Unusual Physical Traits (in addition to their color, or lack thereof!)

Albino bullfrogs behave in all respects as do normally-colored individuals, and like them vary greatly in their dispositions.  The two in my collection are incredibly shy, while a male on exhibit frequently calls during the day, in full view of the visitors.  However, I noticed that mine lacked the solid “feel” that I associate with bullfrogs, and seem not to have very good muscle tone.  They move slowly, and “slide” more than jump from basking sites when disturbed.  Those at the aquarium, and in the possession of a colleague in Louisiana, exhibit similar characteristics. 

All were raised on well-proven bullfrog tadpole favorites (kale, algae, algae tabs, Tetramin fish flakes and bits of fish) and since metamorphosis have been fed a varied, high calcium diet that has always yielded robust frogs in the past – crayfish, minnows, earthworms, well-fed crickets, roaches and wild-caught cicadas, grasshoppers and other insects.

I would greatly appreciate input on this topic from anyone who has experience with albino bullfrogs.

Thanks, until next time, Frank Indiviglio.

Field notes on albino bullfrog tadpoles in the wild are detailed in an article posted at:

http://fwie.fw.vt.edu/vnhs/pdf-files/pdf-full-articles/Full-Bullfrog%20albino%20tadpole.pdf

A visitor to the aquarium exhibit mentioned in this article has posted a video about it, see below

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