Wildlife TV

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Clawed Frogs: Nature’s Pregnancy Test

Mating and breeding are fundamental aspects of surviving as a species and although many animals have breeding seasons, humans as a species, do not. This means that women don’t have specific times during the year in which they are more fertile and willing to engage in mating in order to get pregnant. Instead, we go through monthly fertile cycles between the first menstruation (menarche) and menopause. This is good on one hand because it is not necessary to wait for a specific month or months of the year in order to get pregnant but also bad because, as it can occur at any given time, women might fail to notice they are pregnant and not take basic pre-natal care to ensure the survival and best development of the baby.


Old school pregnancy tests

For many reasons it quickly became important to find out if a woman was pregnant or not as soon as possible. Was the queen finally going to provide an heir? Was the future virgin bride not so virgin after all? Was the husband that had just come back from the sea really the father? Being able to tell, with a certain accuracy, if a woman was pregnant or not would solve many problems but we still have no idea how our (very ancient) ancestors were doing it (if they were at all) since no information was ever found. We are aware however that the first known pregnancy test started to be used in the ancient Egyptian and Greek cultures with the use of urine and grains. They would introduce, on one side, urine of the lady that wanted to find out if she was pregnant, and on the other side (as the control subject) the urine of a priest, on bags of barley and wheat. Both bags would be observed for how long germination would occur. If a lady was with child her grains would sprout a lot faster than the priest (we could easily infer he would not be pregnant).

Throughout history many other “urine analysis” techniques were used to find out if women were pregnant, some of them more scientific than others; but it wasn’t until the last century that animals started to be used in the procedure.

With the discovery that the hCG (human chorionic gonadotropin) hormone was produced by the placenta during the first trimester of pregnancy, scientists were able to design a better and more reliable way to test for pregnancy.

This discovery, in the 1930’s, boosted the development of pregnancy test worldwide with very big implications. For the first time in known history, scientists were using live animals such as mice and even rabbits for their testing. Infantile females (non-sexually mature) were injected with the urine of the woman to be tested and later on killed and dissected in order to look for the presence of ovulation in the animal. The ovulation would have been triggered by the hCG presence in the injected urine of pregnant women and would pose as a positive result.

This method, however, meant that for every tested woman we would end up with a dead mouse or rabbit. Luckily for humanity shortly after, still in the 1930’s, a gentleman named Lancelot Hogben found out that he could use a specific genus of frogs, the Xenopus, to get the same results but without having to kill the animal.


Xenopus: 1930’s-1950’s pregnancy test

Clawed frogs (Xenopus) were subjected to the same method; the urine of the woman was injected in its dorsal lymph sac and if the frog produced eggs in the first 12 to 24 hours the woman was with child. The big difference between mice and rabbits and these frog species is that amphibians, unlike mammals, have external fertilization so the new eggs could be easily observed without having to kill and dissect the animal.

By the 1940’s, this test, named the “Hogben Test” in honour of its discoverer, was already widely used in hospitals.

Many facts helped this method achieve worldwide recognition:

  • It was extremely accurate
  • It was very easy to perform
  • Results were achieved in 12-24 hours
  • The frogs were easily bred
  • The frogs were conveniently kept in aquariums
  • Amphibians in general have large eggs which can be easily examined and manipulated
  • Eggs are released outside the animal (they use external fertilization)
  • Clawed frogs reacted to the hCG hormone released by pregnant women
  • Since the frogs didn’t have to be killed and dissected in order to have their eggs examined, they could be used multiple times
African Clawed Frog (Xenopus laevis)

African Clawed Frog (Xenopus laevis)
Photo Credit


Pregnancy tests post-Xenopus

Even though there were many advantages to using this African species in laboratories all over the world, there were a few cons that ultimately made the test obsolete.

  • The clawed frogs (Xenopus) had to be imported from Africa in large numbers
  • Live animals need to be housed, fed and taken care of
  • One disease outbreak in a lab with frogs would be enough to close it down


Eventually science evolved enough that by the 1960’s the Hogben test became obsolete and today we can buy a small, cheap and easy to use pregnancy test that will give a result within minutes and without going through several technicians, scientists and doctors. The same result can be achieved in private and in minutes.

Unfortunately, all the Xenopus testing for decades came with a price. In 2006 researchers found out that this genus might have been the carriers of the (in)famous chytrid fungus, a deadly amphibian fungus that caused the mass extinction and population decline of almost 200 amphibian species all around the world. African clawed frogs are known to be one of the only species of amphibians in the world to be not only immune but also a carrier of this deadly fungus and several decades ago we shipped them all over the world..

There is no treatment for this fungus and the only way to control this mass extinction is through quarantine.A staggering 30% of known amphibian species are currently threatened with extinction  and about 500 amphibian species are so threatened at the moment that no human effort will be fast enough in order to stop its extinction. Projects like the Amphibian Ark are doing their best to help the remaining species we have surviving these dark times. If you can, visit their “How can I help?” page. There are many things all of us can do to help out, either by donating time, money or skills.

Small gestures can make a huge impact on these small creatures.


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Living in the African Bush

Life in the African Bush can be quite exciting and unpredictable; that is one of the biggest reasons why so many tourists come to Africa every year. It allows us humans to get in touch with a more primal aspect of our existence: the possibility of encountering predators that can and will kill us if given the chance.

For that matter, growing up in the wild areas of Africa is very very different from growing up in Europe. Nick and I are “Europeans”. We were born and raised in UK and Portugal respectively and even though we love the wildlife and have decided  to move to South Africa to be closer to it, we’re very aware of its dangers and necessary daily precautions.

Today I have decided I would like to make a little list of the things that we have to be careful during the day while living in a game reserve with wild animals such as lions, leopards, cheetahs, white rhinos, elephants, buffalo, dozens of species of snakes, spiders and scorpions, and much more.

Our living area is not fenced at all so in theory (and in practice) animals can come and go as they like and if we are lucky (or unlucky) we get to see them.

Our day starts in the morning with the “shoe check” which is pretty much making sure that there are no scorpions, spiders, lizards or bugs inside our shoes before we put them on. Last thing I want to do with my day is being driven all the way to the nearest hospital (over 2 hours away) because a scorpion stung me while I was still half asleep. Going to the bathroom during the night is also an adventure since I must make sure there’s nothing in the slippers before I put them on in the dark and then make the “bathroom check” while my eyes are still barely open.

The “bathroom check” is very similar to the shoe check. It mainly consists of checking out if there are any snakes behind the door, in any corner or behind the toilet before I approach it. If that part is clear I then proceed to check out the toilet itself for spiders, scorpions, lizards or any bugs before I sit on it. After I’m done I make sure that the toilet door is properly closed in case something decides to crawl in the window during the night. At least that way it will remain in the bathroom or crawl back out before I notice it.

After going to the bathroom and putting the clothes on we must confirm that all windows and doors of the house are closed before we head off. Baboons will take advantage of any little entrance they can find and getting back home just to find that all food is gone and the house has been trashed and defecated all over is not my idea of a great end of the day.

Once actually outside the house we must confirm that there’s no animals around the path. During the day most predators would be already gone but sometimes elephants like to just walk by undisturbed. Do you know where a 7 tonnes animal goes to? Anywhere he wants to…

Smaller herbivores are also seen around the area often. We have a couple of Klipspringers living just behind our house and they are very territorial animals. They are tiny but can get aggressive if they feel you are in their way, and like any animals with sharp horns they can do a lot of damage if struck in a bad area. Just a few months ago an elderly lady was killed when a Nyala accidentally(?) pierced her in an artery.

There are paths with gravel where we are which makes it easier to avoid snakes while walking however sometimes we have to walk through rocky areas to reach some other more remote areas. Rocks harbour many species of reptiles, arthropods and rodents, most of them quite harmless but it’s always better to be safe than sorry. During Winter times many species will be dormant and there’s no need to be extremely careful (although it helps, of course) but as Summer arrives venomous snakes start waking up and moving around, sometimes hiding under those same rocks we walk by every day. Avoiding something you can’t see is obviously quite hard so the best course of action is just to stamp your feet and make a bit of noise while walking past. Most snakes will try to move away if they sense that something is coming their way. If they are not the type to just move away (like the Puff Adder) they will at least make themselves visible and audible to scare off whatever is coming. That way we may see them before we step on them and regret it deeply.

Snakes, scorpions and spiders can also be found in areas where firewood is stored. During the Summer the weather is quite hot and people are not as interested in making a fire as they would be during Winter. For that matter, wood storage areas are good places for some species to be safe and undisturbed for long periods of time. Unfortunately for us, when the time comes to get those wood blocks out we must proceed quite slowly and carefully and definitely not putting our hands there to grab it without checking it with a long stick first in case anything strikes.

Although we are surrounded by trees and lots of wood we can’t just use any of it. Unfortunately some people sometimes decide to be cheap and try to use “free wood” instead of bought ones. This can be deadly since some trees release toxic fumes when burnt that can kill humans. In the African bush even trees are out to get you…

The best course of action is to just use the properly stored wood to make a nice fire on a cold night.

Storing food can also be a problem. When living and working in a commercial area, large quantities of food must be stored for staff and guest consumption. Those areas must always be properly closed and locked with a key to avoid animals (especially baboons) entering and raiding it. Just last week someone forgot to lock the door when they left and a baboon got a few minutes of heaven. For some reason that male decided that he wanted to eat strawberry flavoured jelly. I don’t know if it was the colour, the smell or the taste that appealed to him but if I find a pink poo around that smells of strawberry I’ll know which baboon did it.

Having a nice meal can also be hard in the bush. When it’s hot I like to eat outside and enjoy the breeze and the animals foraging around the waterhole in front of us. Unfortunately baboons are always around waiting for the right moment to strike. Putting down the plate and going inside to grab a drink can be a very bad move. The boldest baboons will immediately go for your plate and steal your meal. If you’re lucky instead of a baboon thief you can just have a bird thief. They eat less but are a lot more persistent and keep on coming back even after you shooed them several times. And worst of all, they might even poo on your head…

Now let’s say your day has been good so far but suddenly the power goes out. If it’s during the Summer this will be a common occurrence due to the strong thunderstorms and the fact that we live in a high levelled area that gets hit by lightning quite often. So what do you do when the power goes off? You obviously go check out the generator room so that we can get some energy back. Now this wouldn’t be a problem if there wasn’t a black mamba living there. Yes, a black mamba. One of the deadliest snakes in the entire world lives just a few meters from my room. Guess who doesn’t leave the room windows open at night?And it’s not even a small specimen. It’s a fully grown up adult black mamba. I haven’t seen him(?) yet but just the reports of its existence make me take the long route around the generator room…

And then you reach the end of the day. The sun goes down and the stars are bright in the sky. Unfortunately humans have not developed night vision which is quite an impracticability when surrounded by predators. If anything needs to be done at night we carry a small torch to be able to scan the area and (try to) check for any predators’ eyes. Seeing them is the least of our problems if they are coming for us though. Both me and Nick are aware of what to do when facing several species at night, the most dangerous around this area being leopards, lions and elephants. Running is always the worst possible option unless you want to die faster so we must be ready to quickly assess the situation and act on it accordingly. We always try to go out together if possible since most predators would prefer to stalk a lonely human rather than one with backup but some other species such as elephants wouldn’t really care too much about that. If you are in their way they will let you know.

For now this is all. Living in the African bush can be dangerous but exciting and if you know the “rules” you have better chances of surviving.

We’ve only been living here for a few months but I’m sure that more “funny” situations will arise in the future and I’ll be ready to write about them.

Keep in touch!




If you liked this entry, make sure you check out our Dangerous Animals category.
Previous Dangerous Animals entries:
When Herbivores Attack: Buffalo & Hippo
Adam Sandler attacked by cheetah in South Africa
When Herbivores Attack: Elephants & Rhinos

How do baby Nile Crocodiles survive?

Previously we’ve seen how the tallest and gracious giraffe babies are able to survive in the wild; today we are going to discuss the survival techniques of another famous African animal, the heaviest reptile in Africa, the scary nile crocodile.


Nile Crocodile hatchlings

The nile crocodile (Crocodylus niloticus) is the largest reptile in Africa and the second largest in the world, with the saltwater crocodile (Crocodylus porosus) in Southeast Asia being the biggest one around.

Among reptiles, the members of the Crocodylia order (crocodiles, alligators, caimans and gharials) are the only ones that offer parental care to both eggs and hatchlings and they have been doing this successfully for millions of years.

These amazing carnivores have been around since the time of the dinosaurs and seem to be planning on staying for a lot longer as, just like the giraffes, they are marked as “least concern” on the Red List.

Unlike most reptiles, nile crocodiles’ males and females often co-exist peacefully in the same water source and there are even cases of cooperative hunting observed in wild groups.

Because of the adults’ willingness to live and work together, hatchlings can profit from having an extra protection that other reptile species would certainly like to benefit from. Once the eggs are laid, they are immediately buried in the sand and ferociously guarded by the female for the three months that takes them to incubate.


Female nile crocodile (Crocodylus niloticus) protects her eggs.

Female nile crocodile (Crocodylus niloticus) protects her eggs from predators.
Photo Credit

Parents protecting their eggs is not that uncommon in nature, however, reptiles protecting their newborn babies after they are out of the eggs is quite unusual and this is what sets nile crocodile parents apart from most other reptile species.

Just before getting out of the eggs, crocodile hatchlings start making a high pitched noise that serves as an indicator for the mother to dig them all out. The mother will then pick up each baby crocodile and carry it in her mouth to the water where they will start trying to catch their first prey. But her job does not stop there. Any baby is small and vulnerable and not even crocodiles are the exception. Adult crocodiles will eat them if they get the chance but as long as they keep close to the mother for the first months she will do her best to help their survival, however, despite all of this, only close to 1% of nile crocodiles that are born will reach maturity.


Newly hatched nile crocodile (Crocodylus niloticus) is gently carried in the mother's jaws.

Newly hatched nile crocodile (Crocodylus niloticus) is gently carried in the mother’s jaws.
Photo Credit


As you can see, sometimes, even despite all the efforts from the parents, the majority of the young that are born of certain species will perish but nature finds a way to keep a balance. Both the nile crocodile and the giraffe face high infant mortality rates but none of them is facing extinct in the near future, in fact, they both seem to be here to stay!


I hope you liked learning about the amazing world of baby nile crocodiles
Do you want to find out how other baby animals survive?
Check out our “Series” page for the list of “Baby Animals: How do they survive?


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