| Good morning. |
| Today, we will continue our study of Crocodylus niloticus by talking about its living habits. |
| We've already discussed the evolutionary attributes that set it apart from its crocodile relatives. |
| Does everyone remember that? |
| Yes, it has an extremely narrow snout, and 3 or 4 rows of protective scales on its back, |
| as compared to 2 rows on other members of the Crocodylus genus. |
| Let's take a look at how these carnivorous man-eaters live, |
| where they live, and finally, whether they really deserve their vicious reputation. |
| To start, I'd like to address a great question posed to me by a student during yesterday's office hours. |
| We talked about the distribution of crocodiles in Africa |
| and saw that they are highly concentrated in the South and West of the continent. |
| This student noticed that on the map displaying the distribution of crocodiles across Africa, |
| there were no crocodiles in the Northern Region, |
| and found no mention in the literature of the existence of crocodiles in the North of Africa. |
| Why might there be no crocodiles in North Africa? |
| Let's save this question for later in the lecture. |
| To find out more about the social habits of the African crocodile, |
| one researcher named Tara Shine of the University of Ulster in Northern Ireland |
| conducted a survey of the wetlands in Mauritania |
| and received reports of 46 crocodiles living in one group, |
| or float as we say when referring to crocodiles, |
| though the usual number is a little less than half of that. |
| In general, crocodiles are more highly concentrated in wet, subtropical environments |
| near bodies of water and rich vegetation. |
| While South American crocodiles thrive in cool rainforests, |
| the African crocodile is more equipped for heat. |
| Though they can survive at the hot temperatures found in some deserts, |
| they're not equipped to handle dry climates |
| and thus cannot survive in places like the Sahara Desert of North Africa. |
| As cold-blooded animals, |
| crocodiles' core temperatures fluctuate from their average of 38 degrees Celsius as external conditions change, |
| thus they need to avoid extreme temperatures. |
| Others live an underwater life, keeping a body temperature close to that of the water. |
| As their own unique method of regulating their body temperatures, |
| some African crocodiles have made dens |
| by digging holes in the ground to provide themselves with a cool, dark place to retreat from the hot African sun. |
| Speaking of the hot African sun, |
| let's go back to the question asked at the beginning of the lecture. |
| We know that there used to be crocodiles in Northern Africa, yet today there are none. |
| What are some possible explanations for this? |
| Some students have suggested that the African crocodile has evolved |
| from a desert creature into a wetland creature, |
| thus causing them to migrate south for more appropriate conditions. |
| Others presume the crocodile was hunted out of Northern Africa by a fiercer predator. |
| While these are intelligent guesses, the real story is a little bit different. |
| The key to this migration is that the Sahara Desert did not always cover the North of Africa. |
| About 8,000 years ago, the land was fertile wetlands perfect for breeding crocodiles. |
| Over time, though, the area dried out and the wetland slowly turned to desert, |
| leading the African crocodile to migrate south to the marshlands they call home today. |
| Some crocodiles did, however, adapt to living in dry conditions. |
| In Mauritania, some crocodiles have learned to survive in an area where they can go up to 8 months with no water |
| by spending the driest of times in what's called a torpor, or short period of hibernation. |
| To utilise every bit of rainfall, |
| these desert crocodiles dig underground caves that collect runoff, |
| thus staying cool and hydrated. |
| During the mating period in November and December, |
| males attract females to their viciously protected territory through a number of behaviours |
| that range from snapping their jaws all the way to sending infrasonic pulses through the water. |
| Afterwards, the female digs a hole up to 60 centimetres in depth |
| to store the eggs for an 80-day incubation period. |
| The female protects these eggs during the period, |
| and sometimes even helps crack the eggs with her snout at the end. |
| These teeth-gnashing carnivores are softer than we think. |
| Although these vicious creatures have attacked humans on a few occasions, |
| the residents are not afraid of them. |
| In fact, they show a great deal of reverence towards these wondrous creatures. |
| Some say that crocodiles bring water to their habitat, |
| so if they leave, they will bring the water with them. |
| Obviously this is not true, |
| but it demonstrates the admiration the inhabiting people have for crocodiles. |
| Generally, crocodiles do not predate on humans. |
| They attack when humans populate the crocodiles' habitat, |
| instilling fear and uneasiness in the crocs. |
| Like any other species, crocodiles are known to attack when feeling fear. |
| There's still a lot more to be discovered about the African crocodile. |
| Researchers want to know more about the population size, |
| how many crocodiles inhabit Africa in all, |
| how they form separate floats, etc. |
| There is still also much to learn about migration patterns, |
| and relations to other populations of crocodiles now found in other parts of the world. |
| Next time, we'll examine a few specific case studies of crocodile populations in Southern Africa. |