What Do You Call a Thousand Tadpoles?

Some people call a group of tadpoles a “knot,” while others call them a “cloud,” or a “school.”  We’ve been contemplating this same question here at the Houston toad program, wondering what to call the army (hey, that works!) of Houston toad tadpoles that will emerge from all of the eggs we have released into the wild. To date, the Houston Zoo’s Houston toad program has produced and released around 144,500 of eggs for release into Austin and Bastrop Counties! With less than 300 wild Houston toads remaining in Texas, we hope that this huge release of eggs will help to bolster the wild population and keep this irreplaceable amphibian off the extinction list.

In my last post I mentioned a cool contraption that our partners at Texas State University devised to keep our toad eggs safe while they develop into tadpoles. These predator excluder devices (or simply, egg cages) are placed around the egg strands to keep a host of predators out; including aquatic invertebrates, fish, birds, and even other amphibians. So are these egg cages working? Are our egg strands surviving outside the safety of the zoo in wild ponds?

The answer is yes! Every strand that has been released has successfully hatched and thousands of Houston toad tadpoles are being observed at all of the release sites. Our tadpoles are of course not the only amphibian tadpoles in the ponds, so how do we know that the ones we are seeing are in fact Houston toads? The tadpoles of many species of amphibians actually look very different from one another in both size and coloration. The Houston toad tadpole is typically very dark colored (black in fact), and they prefer to stay in shallow areas near the bottom (unlike the somewhat similar looking Spadefoot toad tadpoles that swim up and down in the water column).

TSU researchers have observed very large Houston toad tadpoles hanging around the egg cages, which mean that they are surviving. This large knot (or cloud, or school, or army) of tadpoles is rivaling the numbers that were observed back in the 1960’s before the number of Houston toads started to precipitously decline.

We are now anxiously awaiting the emergence of thousands of tiny Houston toad metamorphs from the water (surely, this should be called an “army!”) This will be the last time we see our toad babies before they disappear into the surrounding woodlands, and with any luck many of them will return to the ponds to breed early next spring.  Everyone wish this army of tiny toads the best of luck – they are the future of their species!

Why wait for Easter for an “egg-travaganza?!”

The Houston toad team at the Houston Zoo has been working up a storm this spring – a storm of Houston toad eggs! As of this writing, the team has bred 23 groups of adult Houston toads (the groups consist of either one female and one male or one female and two male) since the middle of February using assisted breeding methodologies. In total, we have produced ~80,000 Houston toad eggs!! This is more than twice as many as we produced last year and is a tremendous success for our program!! However, I’m sure you are all wondering just what in the world are we doing with all of those eggs??


Each and every one of the Houston toad egg strands produced at the Zoo going back to the wild to help augment the wild population.  Researchers from Texas State University (TSU) are strategically placing the egg strands in two counties, Austin County and Bastrop County, which are in the historic range of the Houston toad. Both of these counties still harbor small, wild populations of Houston toads that are being monitored by TSU and USFWS.

Researchers from TSU and Houston toad staff and interns are placing the eggs inside protective, wire cages as the strands are placed into the release ponds. Cages? What are those for? One of the biggest complications for the Houston toad recovery effort is that everything LOVES to eat Houston toads – especially their eggs! Birds, fish, aquatic invertebrates, raccoons, you name it; they all love to snack on tasty toad eggs. The cages prevent these hungry critters from feasting on these precious, endangered egg strands, helping to ensure that many of these eggs will survive to make tiny toadlets!

TSU researchers are monitoring each of the release sites and are on the lookout for Houston toad tadpoles and metamorphs. Are the cages working? Are the eggs going to hatch? Stay tuned to find out!

We’re Not Just Toad Keepers, We’re Matchmakers!

The Houston toad team spends countless hours performing the traditional tasks associated with caring for animals.  These tasks includes the cleaning, feeding, medical treatments of the Houston toads, as well as  water quality testing, care of the invertebrate cultures, and the general maintenance of the toad facility. However, did you know that the team is also responsible for being toad “match-makers” during the breeding season? Yup, that’s right. Not only are we handy with pH testing strips and power drills, we can also provide professional dating recommendations to Houston toads (now try writing that up on YOUR résumé!)

toad blog feb

Like many other endangered species, the breeding of Houston toads is managed a Species Survival Plan (SSP), which is a document produced by the Association of Zoo and Aquarium’s Population Management Center. The SSP takes into consideration the known genetics of a group of animals and makes recommendations as to who the animals should be paired with.  With these guidelines in hand, the Houston toad team evaluates each individual toad from a group of toads approved for breeding, and assesses their health and size. Breeding pairs (or triplets, often one female and two males) are then grouped accordingly. This year we evaluated and paired over 170 individual toads!

toad blog feb 2

Breeding Houston toads is not as easy as placing a male and female toad together. In fact, it is very difficult (but not impossible) to encourage natural breeding captive environments. Here in the toad facility, we use a hormone assisted breeding protocol to ensure successful breeding in our Houston toads. This protocol takes place over the course of several days, and requires a concerted effort between the Houston toad team and the zoo’s veterinary staff.

It would be impossible to breed all 170 toads at one time, so this spring we are staggering the breeding attempts over the course of two months and setting up 6-8 breeding pairs a week. We are happy to announce that our first round of breeding (that ironically began on Valentine’s Day) was a huge success! Out of the 8 total pairings set up, we produced 7 strands which totaled around 27,000 eggs!

So now that our matchmaking efforts were a success, what’s next? Stay tuned to the next blog post to find out what we are doing with all those toad eggs!

Finding the Wily, Wild Houston Toad!

While many of us are enjoying these cool, winter evenings indoors in front of the TV with our favorite snack, Houston toad researchers are bundling up, grabbing a thermos of coffee and hitting the road to find the  elusive Houston toad! After the first heavy rain of the year, often near the end of January, Houston toads are hitting the ponds to look for mates.  The Houston toad spends the majority of the year in shallow burrows to escape the extreme Texas temperatures (a process called estivation); therefore the best opportunity to find and count toads is during their breeding season when they are out and about.

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Houston toad male calling

Though some toad biologists slip on a pair of rubber boots and put on a headlamp to look for Houston toads using sight, most researchers search for toads using sound. Sound? How does that work? The Houston toad males have a very distinctive advertisement call, which is the call that they use to tell female toads “Hey, lady! Check me out! I’m over here!” In fact, all species of frogs and toads have a distinctive call that they use to get the attention of the opposite sex. Interestingly, it is not just the males that do the calling. In some species, including another local frog species called the gray tree frog (Hyla versicolor), the females will both call and counter-call (which means to call back) to the males. To hear a Houston toad call, check out the following link:   http://www.californiaherps.com/noncal/misc/miscfrogs/pages/a.houstonensis.sounds.html


USFWS biulogists depolying a SongMeter

To find calling toads, researchers set out in their cars after dark to literally “listen” for Houston toads. The areas that are visited have been previously identified as suitable habitat for the Houston toad, or are locations where Houston toads were either found or heard in the past. The surveys follow a very systematic pattern with dozens of stops, and they often take hours to complete. This year, for the first time in several years, five Houston toad counties are being surveyed at once lead by research teams from Texas State University and USFWS. Fingers crossed that we’re going to find some wild toads!

Another way that researchers find wild Houston toads is through the use of a recording device called a SongMeter. A SongMeter is specifically designed to detect the auditory calls of wild animals.  To detect Houston toads, SongMeters are placed in trees near ponds and are programmed to record sounds during the course of the night. These devices can record two weeks’ worth of sound data! A software program is then used to find the particular waveform that correlates to the Houston toad call. Of course, every Houston toad “hit” found by the software program has to be verified by human ears, which requires hours of listening time.

So over the next couple of months while you’re enjoying your favorite evening TV show, take a moment to think about the field researchers braving the chilly, wet Texas nights on the hunt for the Houston toad. Each toad found (or heard) tells us more about the health of the wild population and gives us another critical piece of information concerning the natural history of this rare species. Good luck toad folks and Godspeed!

It's Houston Toad Time!

The toad team at the Houston Zoo hopes that everyone had a wonderful winter holiday. Like a lot of people, we have also made some “resolutions” for 2014; however, they don’t involve hitting the gym or finding a hot date!  Instead, we have resolved to release thousands of Houston toad eggs into the wild in and around Bastrop State Park this spring – how about that?!

Houston toad eggs.

While most amphibians are still tucked away in their winter hiding places, the Houston toad is getting ready for the breeding season. The Houston toad breeding season typically starts in late January or early February and can last until the first of May depending on rainfall.  The first heavy rains of the year generally signal the start of the breeding season and though it is pretty cold this time of year, as long as the nighttime air temperature is around 50F, the toads will come to the pond to find a mate!

Just like the wild toads, we are also gearing up for breeding season here at the Houston Zoo.  Like many endangered species that are bred at zoos, the Houston toad program has a breeding plan (called a Species Survival Plan, or SSP) that was designed by toad biologists and the Association of Zoos & Aquariums’ Population Management Center.  Using this plan, specific groups of toads are selected to breed with each other to ensure genetic diversity.

Because we are a release program, we have to make sure that each individual toad is free of any potential pathogens that could be passed to the eggs and then spread out into the wild.   We started an extensive disease screen in October of 2013, and to date we have cleared 90% of our breeder toads!


Interestingly, the weather plays a huge role in our breeding schedule. It would be silly to produce thousands of toad eggs, then not have any ponds to place them in! We very carefully watch the weather before we decide to breed and release eggs. In fact, because the weather and environmental conditions are so critical, we heavily rely on field researchers from Texas State University and USFWS to help us make the decision to breed. Everyone please continue cross your fingers for rain, the Houston toads need it!

The Houston Zoo and our collaborators at the Fort Worth Zoo, Dallas Zoo, Texas State University, and USFWS are gearing up for a huge release of Houston toad eggs this year.  This concerted effort has never been attempted before, but we are excited and ready for the challenge! Could 2014 be the year of the Houston toad? Stay tuned to find out!

Is That a Houston Toad Hopping in my Yard?

The Houston area has been very fortunate so far this summer to have had rain. Not only is the rain keeping our outdoor plants and trees alive, it has also increased the activity of many nocturnal critters, especially amphibians!  After a good rain, we get lots of emails here at the zoo from people wondering what sort of frogs and toads they are spotting  around the places they live.  In this post we will discuss the three, most common amphibians that you have seen (or heard) around your house or apartment in Houston!

1) Gulf Coast toad (Incilius nebulifer) – This toad is the most common amphibian found in everyone’s backyards, school play grounds, bayou easements, and parks. These hardy little critters can live almost anywhere as long as there is some access to water. Ever find a toad sitting in your dog’s outdoor water bowl? It is most likely a Gulf Coast toad. Because they have a somewhat similar appearance (thickened, warty skin that is dark brown, tan, and green in appearance) many people mistake Gulf Coast toads for Houston toads; however, Houston toads haven’t been found in Houston for more than 20 years.  To learn more about the differences between a Gulf Coast toad and a Houston toad, please check out this video.

2) Rio Grande Chirping frog (Syrrhophus cystignathoides) – Have you ever been outside at night and heard what you though sounded like a bird chirping in the bushes? What you heard is not a bird at all, but a tiny little frog! The Rio Grande Chirping frog is a little over an inch long and often brown or yellowish green in color. Because they are so small they are often very difficult to spot at night hiding in the bushes, plants pots, or in leaf litter. Though they are originally from northern Mexico and the Rio Grande Valley in Texas, these little frogs are increasing their range due to the transport of pots and plants from these more southern areas!

3) Green Tree Frog  (Hyla cinerea) – The Green Tree Frog can be commonly heard in neighborhoods and parks around Houston that have both trees and water.  Good places to listen for these frogs in the evening are Terry Hershey Park, the arboretum at Memorial Park, as well as Herman Park and the Houston Zoo.  These very green frogs (hence the name) are around 2.5 inches long and have a white stripe down the sides of their body. These frogs sound like a duck when they call at night and many people mistakenly think that they are hearing waterfowl roosting in trees!

To learn more about how to tell the difference between the different toads in our area, please visit the Houston Zoo’s “Know your Toad” page.

Think you’ve heard one of the above amphibians call? Check out the following pages to double-check!

Gulf Coast toad information


Houston Toad Release: Round 3

We are pleased to announce our third Houston toad release for the year! Last weekend, we delivered 200 juvenile toads (each averaging only between 1 – 2 grams) into an area outside of Bastrop State Park. We have now released three major life stages since March of this year – eggs, juveniles, and adults.

little toad

The toadlets released last week were from the same egg strands that were delivered to areas adjacent to Bastrop State Park in May. One of the zoo’s critical roles in the Houston toad recovery program is the maintenance of a captive assurance colony; therefore we keep back some individuals from each strand produced at the zoo that is destined for release. The captive assurance toads are in essence a “library” for the toads that we release to the wild.  These individuals that we keep will also become our breeders in the future.

We kept ~50 eggs from each of the egg strands released in May, expecting that many would not survive; however, almost all of the eggs we kept made it all the way through metamorphosis, producing too many captive assurance toads for us to keep! (This is certainly not a bad problem to have!) We contacted our collaborators at Texas State University and arranged for these “extra” juvenile toads to be released at the same ponds that the eggs (basically their brothers and sisters) had been previously taken.

little toad 2

Two of our volunteers, Stephanie (intern) and Jacquelyne (volunteer) accompanied graduate student Melissa (Texas State) and me out to the egg release sites.  The day was overcast and the ground was moist from the previous day’s rain, which are perfect conditions for toads! We placed the juvenile toads under deadfall (dead trees lying on the ground) taking special care to ensure that there was no sign of fire ants. The little toads either disappeared under the logs into hiding, or went boldly off into the woods to explore their new home.  It started raining at the last release site (again, great for toads but it made for a soggy ride home back to Houston). Cross your fingers that these summer rains keep on coming!

Melissa will continue to monitor these ponds throughout the rest of this year and next. Hopefully she will see some of our little guys again in the spring!

My, Do Our Babies Grow Up Fast!

It is hard to imagine that only a few weeks ago that the tiny toadlets pictured in these photos were tadpoles swimming in a tank! Our little toads have grown so fast! Though we typically raise our own small invertebrates to feed the juveniles, these little guys have grown so quickly that we will soon have to start ordering a small sized (1/4 inch) crickets!  toadlet-resize

These toadlets are the offspring of our eggs that we released into the wild in and around Bastrop State Park this past spring. We kept some of the eggs back to raise to “toad-hood” as part of our mission to serve as an ark for the species. Additionally, once these little toadlets mature, they will produce offspring of their own for release in the future!

toadlet2resizeWe have been very successful in raising the tadpoles and subsequent toadlets that we kept back from our releases. Of all the tadpoles that hatched from the eggs, we only lost 5! We now actually have too many toadlets (200+) to keep here at the facility! In the coming weeks, we will once again work with researchers from Texas State University and USFWS to release these little guys back out into the wild. This will mark our fourth release of the year and is the first time ever that we have released three different life stages: eggs, juveniles, and adults!

Many thanks to all of our supporters! We couldn’t do this without your concern for the future of this amazing native Texan. Stay tuned for information on our up-coming toadlet release!

Houston, We Have Legs!

In the last blog post, we discussed how egg and tadpole development can be broken down into various stages, called Gosner stages. The stages start with the fertilization of the egg (Gosner stage 1) and extend to Gosner stage 46, which is when the baby toad (also called an emergent) absorbs all of its tadpole tail.

emergent-with-tailLate last week, one of our tadpole tanks reached the developmental stage that we have been carefully monitoring for – Gosner 42! Gosner 42 is a really important time point in metamorphosis in which the tadpole starts to develop lungs. This means that the tadpole will soon give up its aquatic lifestyle for a new life on land.

We know that tadpoles are reaching this critical time point because they start to grow their front limbs. Did you know that both limbs don’t “sprout” at the same time? While we are monitoring for Gosner 42 stage tadpoles, it is not uncommon for us to see tadpoles swimming around with three legs!

Once one front leg is observable on a tadpole, we carefully collect it from the tank with a net and transfer it to a tank with shallow water and moss. This setup allows the tadpole access to both water and land as it finishes transitioning from gills to lungs.

As of today, we have 19 emergents from our first round of breeding several weeks ago. Several of these little guys still have some of their tail remaining, while others look just like tiny toads! Each emergent weighs less than a gram. It is hard to imagine that in a year they will weigh from 20 to 50 grams!


We are currently also caring for 47 tiny little toads that were head-started by our collaborators at Texas State University. These little toads are from egg strands collected around the Bastrop area and are the first wild toads to be brought into the facility since 2010. These toads will hopefully add “new genetics” to our captive colony, which is important so that we can maintain high genetic diversity in the eggs, larva, and toads that we release back into the wild in the coming years.

Stay tuned as we post more updates our newest additions!

Raising a Houston Toad

So what does it take to raise a Houston toad from an egg? A lot of water quality testing, algae paste, and some good ol’ fashioned TLC.

The Houston toad facility at the Houston Zoo has four sets of tadpole racks that are designed to raise eggs to tadpoles. The racks themselves are made up of four aquariums with a circulating water system that runs through a set of filters. Water quality is of upmost importance, and the water is tested for the presence of nitrogen waste products every day.  Additionally, old food and debris are removed on a regular basis. The water in each rack is replaced as needed to keep it as clean as possible.

Unlike the carnivorous adults, Houston toad tadpoles are primarily vegetarians. In the wild they eat a variety of aquatic plant matter, as well as pine pollen that falls on the pond’s surface.  Here at the zoo the tadpoles are fed algae wafers and an algae paste that is smeared on pieces of PVC (which sinks to the bottom where the tadpoles like to feed). Older tadpoles are fed pieces of sweet potato and bok choy for additional vitamins and minerals.

As the tadpoles grow, they start to show distinct physical characteristics that can be used to determine what stage of metamorphosis they are in. The characteristics have been broken down into specific developmental time points called Gosner stages.  For example, when tadpoles start to develop a mouth they are in Gosner stage 23, Gosner stage 26 is when the hind limbs start to form, and Gosner 42 when the front limbs start to form.

We carefully monitor the tadpoles when they get close to Gosner 42. It is at this point that we collect the tadpoles from the tadpole tanks and transfer them into a separate tank with shallow water and moss. Not only are the tadpoles forming their forelimbs at this point, but they are also changing from using gills to lungs; therefore, it is very important that they have a surface that they can use to crawl up and out of the water!

We monitor the little toadlets until they completely absorb their tadpole tail. Did you know that the tail is the little toad’s first meal? Yummy! Once they absorb their tail they are carefully moved to another tank designed with shallow water and lots of moss that they can hop around on. In these tanks the toadlets are fed tiny insects called springtails.  As they grow they are offered larger food items, such as baby crickets (called pinheads), fruit flies, bean beetles, and eventually crickets.

Currently, we have 6 tanks of tadpoles that we are caring for that will eventually make toads that will become members of our captive assurance colony (which means they will be parents in the future!) Our oldest tadpoles are just now growing out their back legs (Gossner 28). We’ll keep you posted on their progress!

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