Imagine checking out at the grocery store, and as you politely socially distance from the customer in front of you, your eyes land upon a new tabloid.  It’s a special edition, The Aldabra Enquirer!   The shocking headlines include, “Both Males AND Females promiscuous, expert says!   Truth revealed – Esmeralda is actually a MALE!   “I ran for my life when I saw them NOSING!”  “Heartless parenting, scientists declare”  “It must have weighed 600 pounds, and it was coming right for me!”  and finally, “Vacation in the Seychelles? Think again…what about the Aldabra CREEP?

Like most tabloids, The Aldabra Enquirer includes a grain of truth in each headline, so read on to learn about these amazing, ancient giants!

The Gigantism

Aldabra tortoises and their more famous cousins, the Galapagos Giant Tortoises, evolved from a common ancestor about 20 million years ago, and the Aldabras dispersed from Madagascar to the islands of the Seychelles, and also to Mauritius, Reunion, Rodrigues, and Zanzibar.    Originally they shared these islands in the Indian Ocean with many other species of giant tortoises, but today only the Aldabras remain.   Again like their cousins the Galapagos, they were prized by seafarers as the perfect source of food for long voyages, and were often stacked like firewood in the holds of ships.  The short version is that their numbers decreased significantly, and they disappeared from everywhere except the Aldabra Atoll (and a few individuals have been relocated to zoos and to some of the neighboring islands and cays).      The Aldabra Atoll is part of the Seychelles (it’s around 930 miles east of Africa, and it’s northeast of Madagascar), and is the world’s largest atoll, which is a ring-shaped coral reef.   Today, the giant tortoises on Aldabra number from 100,000 to about 150,000.  

There are various theories about why certain types of tortoises grow so large, but the one currently favored by the scientific community is the “founder effect,” when only a few individuals of a species arrive in an isolated place, like an atoll.   If abnormal genetic traits, for example mutations like gigantism, enable them to better survive in this new environment, the small populations of survivors will inbreed.  And because the genetic trait is advantageous, natural selection sees that these traits become fixed in this isolated population.     That explains why the giant tortoises are endemic only to islands and atolls, never to mainlands.    

But How Big is Giant?

The largest Aldabra tortoise documented weighed in at about 672 pounds!   We know this must have been a male, because they are considerably larger than females.   The male Aldabra’s carapace, which is the upper shell, can grow up to 4 feet long, and they generally weigh around 550 pounds.   The females are considerably smaller, but relatively a little tubbier – 3 feet long on the carapace and 350 pounds.  Aldabras grow pretty slowly, and when they’re 25 years old, they’re ready for breeding, though they’ve reached only about half of their full size.  

 Scientists speculate that these tortoises don’t grow continuously, and further that the growth rate slows as they get older, which means they’re not necessarily full-grown when they reach their 50th  birthday, or “hatch day.”  They are suspected of having very long life spans – perhaps up to 170 years – but because research scientists can’t compete with that impressive statistic, even those devoted to the species for their entire lifetimes can’t verify this.   No members of the species have been in human care that long, either, so even in an environment that can be controlled, experts always say, “This individual may live to about 170.” 

Not exactly role models for family life

Yes, promiscuous is an apt description!  This shocking headline from our fictional Enquirer is accurate – but scientists prefer to describe Aldabras’ mating habits as polygynandrous.  Both males and females have multiple partners.  Time to now picture the relative sizes of the males and females – we might predict that the weight difference alone could make coupling dangerous for the females.   However, they hold their own, and when they want to get rid of an aggressive male who is attempting to breed, they simply extend their front legs to make themselves as tall as possible;   this has the effect of dropping the back of the shells to the ground, swiftly causing an unwanted male to tumble off and trudge away.  Even without this neat trick, most mating attempts are unsuccessful, and though a female may lay from 9-25 eggs, only about half will be fertile.

Odds are not good for those 12 or so fertilized eggs, either, because like many tortoises and other reptiles, females lay the eggs and walk away.   These rubbery, tennis-ball sized eggs are not even buried, because the nests are shallow indentations on the ground’s surface.  Eggs therefore are especially vulnerable to predators (like giant crabs) as well as climatic events like flooding or rising temperatures.  And those who do hatch are totally on their own.    Fortunately, their herbivorous food sources, like grass, and small plants, are at ground level.  

 A Day in the Life

But let’s say a lucky hatchling does make it to adulthood, where her only predator would be a human being.   What does she do with her day?    Well, sleeping is quite popular – up to 18 hours a day.   Then there’s grazing – as the Aldabras become larger, they’re able to eat tasty treats above ground level, often by knocking over small trees and shrubs – and this is actually beneficial to their ecosystem. So like elephants, the Aldabra Giant Tortoises are a keystone species, enabling the survival of many other  creatures on the atoll who might depend on these food sources as well.   These hefty giants also create pathways for their fellow atoll residents.     Like all herbivores, Aldabras also provide the useful service of dispersing seeds through their feces, and there’s actually a species of land hermit crab, Coenobita rugosus, whose entire diet consists of Aldabra feces.  

So let’s see – sleeping, grazing, landscaping , defecating…..then there’s stretching,  a little walking (0.3 mph), resting, mating (or not), and nosing.  Nosing?   Nosing is actually kind of endearing, even though researchers have no idea of its purpose in the lives of these generally unsociable creatures. But anyway, one thing scientists are sure of about nosing is that it has absolutely nothing to do with mating.  What happens is this:  One Aldabra will lie down next to another, and then proceed to rub his or her nose on the companion’s head or neck, and continue doing so for several minutes.  Then it’s time for more sleeping, probably, or maybe walking away, slowly of course.     By the way, one of the names for a group of Aldabras is a “creep.”     

Are they endangered?

The good news is that the Aldabra Atoll has been designated as a UNESCO World Heritage Site, and that means the tortoises are protected there.   However, the IUCN has designated them as Vulnerable, just a step below endangered, and this is due to habitat loss as well as the introduction of introduced mammals which compete for land and resources, and also prey upon Aldabra eggs.   And the greatest threat now seems to be rising sea levels around the atoll – which is projected to cause up to a 65% decrease in tortoise population on Aldabra Atoll in the next century.  There are breeding programs in AZA zoos, but unfortunately, not many have yet been successful (similar to what happens in the wild). But maybe the continued opportunity to observe these unique creatures will result in new insights into breeding them – We hope so!

At the Reid Park Zoo

You can visit the creep at the Reid Park Zoo – it consists of two females,  Georgie (maybe about 32 years old and about 155 pounds)  and Dulcee (maybe about 73 years old and 192 pounds), and the gigantic Herbie, who’s clearly the male, maybe going on 90, and weighing in at about 533! It’s a sure bet you’ll see them indulging in one of their nine activities – maybe even nosing.   And if that whets your appetite, you’ll soon be able to see more marvelous reptiles in the Reid Park Zoo expansion – and each one will have its own unique adaptations and behaviors – but how can any of them compete with nosing?

NOT SO FAST –  WHAT ABOUT ESMERALDA?????

Oh yes – our final shocking headline proves that if you don’t see the relative sizes of male and female Aldabra Tortoises, it’s awfully difficult to determine the gender of one of these giants.    Esmeralda lives on Bird Island, a tiny coral cay in the Seychelles, and he weighs 670 pounds.  He’s maybe 170 years old.   And he got his name from a famous botanist and zoologist named Lyall Watson, who happened to be  visiting Bird Island.  A giant Aldabra Tortoise unconcernedly approached the zoologist, and he just seemed so mellow and happy that Mr. Watson, who only checks the gender of reptiles when he’s researching them, felt Esmeralda was the perfect name, and it stuck.    No worries.    To paraphrase William Shakespeare, “A male Aldabra Tortoise by any other name would still be as huge.”

Come to the Reid Park Zoo and take a gander at Herbie – you’ll see what we mean!

What is bright green, lives high up in the trees, and has over 100 teeth?

A Green Tree Python! These arboreal snakes are born yellow or brick-red and turn bright green as they mature. Their vivid color, with a pattern of spots and stripes, provides a perfect camouflage. They can be virtually invisible in the tropical rainforests of New Guinea, eastern Indonesia and the northeast Cape York Peninsula of Australia. They have a prehensile tail (capable of grasping) that helps them climb trees and also plays a devilishly clever role in hunting.

They rest coiled horizontally on tree limbs forming a ‘saddle’ pose with their head resting in the middle, which is also a good position to collect rain water.  In the hunting position, the head is looking down ready to strike, and they often dangle and wiggle their worm-like tails to lure curious prey. This coiled position allows them to spring into action for a quick capture and instant immobilization of a tasty meal.   These ambush predators are patient hunters, moving infrequently; in fact, to avoid being revealed, they typically only change positions during dusk or dawn.  

Green Tree Pythons are non-venomous constrictors.  Those hundred teeth are backward-facing, and primarily keep the captured prey in place until it can be eased down into the digestive tract, because  they swallow everything  whole.   They eat small mammals, rodents, frogs and other amphibians, birds, and other reptiles, like lizards, and though they’re capable of moving down from the trees to the ground, most of what they need comes to them and their wiggling “worm” high in the tree canopies.  Juveniles are diurnal (active during the day) and hunt smaller animals.  Adults are nocturnal and hunt larger mammals and reptiles, since they can open their mouths wider.   Although they spend most of their time in the trees, Green Tree Pythons occasionally will come down to the base of a tree and use their sight and heat-sensing labial pits  to locate an unlucky victim. 

Colorful Babies

Green Tree Pythons have a seasonal breeding cycle; however, it is believed that they do not breed every year.  The females prefer to nest in hollow trees and will have a clutch of about 5-35 eggs. Females protect and warm the eggs by wrapping around them with a ‘muscular shiver’ to produce heat. Eggs hatch after about 50 days, normally in October or November.  This coincides with the beginning of the wet season, ensuring that there will be ample food supply.  About 12 inches in length when hatched, the baby pythons’ brick-red or yellow color is great camouflage and blends into the  low-lying tree branches on the forest edge, where smaller animals reside.  Here they can find lizards and small insects.  The color change to the vivid green occurs between six and twelve months when the young python is about 22 inches long and is moving higher up the tree in search of larger prey. This “greening” is complete at about 2-3 years of age and these beautiful and resourceful pythons can grow to be about five feet in length. 

If it looks like a Green Tree Python….

The Green Tree Python and the Emerald Tree Boa are examples of convergent evolution.   Although they live on different continents and are not closely related, they look and act like each other and are found in similar habitats. Both live in tropical rainforests and consume diets that are alike.  Both share the same resting and hunting positions. Both have red colored juveniles and both become bright green as adults. There are also significant differences, though.   The Green Tree Python has finer scales and a more rounded nose.  The Emerald Tree Boa has another row of heat pits above the mouth. The yellow color of the young Green Tree Python is never found in the Emerald Tree Boa, and The Green Tree Python is oviparous (lays eggs) while the Emerald Tree Boa is ovoviviparous (live births).  

Conservation

The green tree pythons are beneficial to their ecosystem by helping maintain a balance of rodents, birds and lizards.  They also are food for several animals such as raptors, owls, dingoes and mangrove monitors. This species is at risk due to reptile enthusiasts collecting them for the pet trade, as well as loss of habitat due to logging. Fortunately, their IUCN conservation status, last assessed in 2017, is ‘least concern’ at this time.   Let’s hope this doesn’t change.

Meet Diego and Frida

Reid Park Zoo has a pair of Green Tree Pythons.  Diego and Frida  moved to Tucson in 2008.  They are contentedly housed in the Conservation Learning Center and are always on display, so you can safely get a really good look at them.      It’s fun to visit and observe them closely – see if you can identify the “saddle position” or one of their tails looking deceptively wormlike – but remember, they want to be as still as possible in order not to tip you off!    If you’re bringing children who might be afraid of snakes, you might enjoy reading ‘Verdi’ ahead of time.  It’s a wonderful children’s book by Janelle Cannon, which explains the color change of a young Green Tree Python, as well as the challenges of life in the rainforest treetops.

It’s exciting to think of all the reptile relatives that will soon live nearby in the Reid Park Zoo expansion, but no matter what showy reptiles come to live in the Pathway to Asia, (like a Komodo Dragon!)  Diego and Frida will still rank among the most beautiful creatures of their kind.

From that tiny common side-blotched lizard scurrying under your garage door to the bold Eastern Collared Lizard calmly basking right in front of you, our desert lizards have amazing ways to survive and thrive. If you’ve lived here a while, you’ve probably encountered hundreds of them. But now, Tucson, it’s time to meet The King of the Lizards.

The Reid Park Zoo’s expansion will be bringing us the biggest lizard on earth – the Komodo Dragon. These real-life fairytale creatures are huge, they’re fascinating, they’re apex predators, and they’ve been around for 100 million years or so. And though they have no natural enemies, they’re now vulnerable in the wild.  

They’re Huge.  And Hungry.

These giants average about 10 feet long and 154 pounds for males, and the largest Komodo Dragon on record was 10.3 feet long and weighed 366 pounds. And they’re incredibly strong, especially in the muscular jaw and neck area. They are such efficient eaters that they can eat up 80% of their own body weight in just one day. Luckily, their stomachs can expand. And they have another useful trick for that sluggish feeling you get after overeating. If they sense a threat and need to flee quickly, they simply throw up their stomach contents and lose the extra weight.

What about that fearsome bite?

The Komodo Dragon is an ambush predator, lurking patiently by the side of known wildlife paths to conserve energy, then leaping and striking when a tantalizing animal passes by. Its favorite meal in the wild is the Timor Deer, but it will eat anything from large water buffalo to its own newly-hatched offspring.

The Dragons’ teeth are large, they’re sharp, and they’re serrated. They’re also breeding grounds for bacteria, since their particular brand of oral hygiene, leaving scraps of their previous meals on and between their choppers, encourages the development of around 50 different bacterial strains. Seven of these are highly septic and thrive in the dragons’ saliva. As if that weren’t enough, researchers have also located a venom gland in the lower jaw, and that venom happens to be an anticoagulant. The effects of a dragon bite are generally profuse bleeding and the onset of sepsis. The victim will often flee, but after a few days, will surely succumb to the attack. And the Komodo Dragon has an acute sense of smell (via its flickering tongue) which can locate its injured prey even when it’s miles away.

Luckily, because the Dragons tend to scuffle with each other when they’re feeling peckish, this lethal bite has no effect – except perhaps for some disfiguration – on their fellow lizard kings.

Those poor little things.

Let’s begin with the hatchlings, whose sometimes unfortunate fate was alluded to above. Komodo dragons are generally solitary, but breed annually, though the female individuals lay eggs only every two years. Clutches are between 15-30 eggs.  But as the females are naturally solitary creatures, if it’s their year to lay eggs, they can always skip the actual breeding and through parthenogenesis, lay perfectly fertile eggs without the assistance of a male. Well, not perfectly fertile – all the “fatherless” hatchlings will be male.

The eggs are roughly the size of grapefruit, and are laid in nests on hillsides, on the ground, or in  mounds which have been vacated by another indigenous species, the orange-footed scrub fowl. Female  Komodo Dragons have also been known to dig decoy nests to protect the eggs from predators, including fellow Dragons. Some females behave in a maternal fashion for the three months of incubation, guarding the eggs, but others, like so many reptiles, simply lay the eggs and abandon them. Hatchlings lucky enough to make it to hatching immediately scramble up the nearest tree, where the heavy, hungry adults of their kind can’t reach them. They’re  about 16 inches long and are precocial – ready to find their own food right away. There’s plenty of food available up in the trees, and the young Dragons will enjoy this arboreal period of their lives for about 4 years, finally coming down when they’re around four feet in length.

The Daily life of an adult Komodo Dragon

The Dragons are indigenous to five islands in Indonesia, four in Komodo National Park (Komodo, Rinca, Gili Montang, and Gili Dasami) and another island outside the park, called Flores.

The mostly solitary life of adult Komodo Dragons consists of four things: hunting, eating, basking in the sun (they’re ectothermic), and lots and lots of sleeping. Most of these require very little energy, and researchers have discovered that even though these reptiles are capable of travelling long distances, they almost never stray from the areas where they and their progenitors have always lived.   

They do have great homing abilities, though, as demonstrated by an experiment in which adults were relocated on their native island, as far as 13.7 miles away from their home. Within four months, all of the dragons relocated on land had returned to their home territories. However, those relocated across a waterway, though they are perfectly capable of swimming, seemed to decide it was too much trouble – or perhaps too great an expenditure of energy, to return to their ancestral homes and adapted to the new locations without much fuss.

Why is this species now considered vulnerable?

Their numbers in the wild are decreasing, largely through human encroachment, habitat fragmentation, the illegal wildlife trade, and the burning of grasslands in order for humans to hunt the Dragons’ favorite prey, the Timor Deer. Also, as evolutionary stars, they generate a substantial amount of income for Indonesia through tourism – where guides feed them unnatural foods to make them drowsy and suitable for photographs with tourists, while those tourists, even if they don’t mean to, are altering the Dragons’ natural environments just by being there.   

The research and breeding of Komodo Dragons that can be safely done in human care is now more important than ever. The Reid Park Zoo hopes you’ll come see this most amazing lizard once the Pathway to Asia expansion is complete! Just by visiting, you’ll be helping the Zoo in their efforts to conserve these ancient and fascinating creatures.