1Good morning.
2Today, we will continue our study of Crocodylus niloticus by talking about its living habits.
3We've already discussed the evolutionary attributes that set it apart from its crocodile relatives.
4Does everyone remember that?
5Yes, it has an extremely narrow snout, and 3 or 4 rows of protective scales on its back,
6as compared to 2 rows on other members of the Crocodylus genus.
7Let's take a look at how these carnivorous man-eaters live,
8where they live, and finally, whether they really deserve their vicious reputation.
9To start, I'd like to address a great question posed to me by a student during yesterday's office hours.
10We talked about the distribution of crocodiles in Africa
11and saw that they are highly concentrated in the South and West of the continent.
12This student noticed that on the map displaying the distribution of crocodiles across Africa,
13there were no crocodiles in the Northern Region,
14and found no mention in the literature of the existence of crocodiles in the North of Africa.
15Why might there be no crocodiles in North Africa?
16Let's save this question for later in the lecture.
17To find out more about the social habits of the African crocodile,
18one researcher named Tara Shine of the University of Ulster in Northern Ireland
19conducted a survey of the wetlands in Mauritania
20and received reports of 46 crocodiles living in one group,
21or float as we say when referring to crocodiles,
22though the usual number is a little less than half of that.
23In general, crocodiles are more highly concentrated in wet, subtropical environments
24near bodies of water and rich vegetation.
25While South American crocodiles thrive in cool rainforests,
26the African crocodile is more equipped for heat.
27Though they can survive at the hot temperatures found in some deserts,
28they're not equipped to handle dry climates
29and thus cannot survive in places like the Sahara Desert of North Africa.
30As cold-blooded animals,
31crocodiles' core temperatures fluctuate from their average of 38 degrees Celsius as external conditions change,
32thus they need to avoid extreme temperatures.
33Others live an underwater life, keeping a body temperature close to that of the water.
34As their own unique method of regulating their body temperatures,
35some African crocodiles have made dens
36by digging holes in the ground to provide themselves with a cool, dark place to retreat from the hot African sun.
37Speaking of the hot African sun,
38let's go back to the question asked at the beginning of the lecture.
39We know that there used to be crocodiles in Northern Africa, yet today there are none.
40What are some possible explanations for this?
41Some students have suggested that the African crocodile has evolved
42from a desert creature into a wetland creature,
43thus causing them to migrate south for more appropriate conditions.
44Others presume the crocodile was hunted out of Northern Africa by a fiercer predator.
45While these are intelligent guesses, the real story is a little bit different.
46The key to this migration is that the Sahara Desert did not always cover the North of Africa.
47About 8,000 years ago, the land was fertile wetlands perfect for breeding crocodiles.
48Over time, though, the area dried out and the wetland slowly turned to desert,
49leading the African crocodile to migrate south to the marshlands they call home today.
50Some crocodiles did, however, adapt to living in dry conditions.
51In Mauritania, some crocodiles have learned to survive in an area where they can go up to 8 months with no water
52by spending the driest of times in what's called a torpor, or short period of hibernation.
53To utilise every bit of rainfall,
54these desert crocodiles dig underground caves that collect runoff,
55thus staying cool and hydrated.
56During the mating period in November and December,
57males attract females to their viciously protected territory through a number of behaviours
58that range from snapping their jaws all the way to sending infrasonic pulses through the water.
59Afterwards, the female digs a hole up to 60 centimetres in depth
60to store the eggs for an 80-day incubation period.
61The female protects these eggs during the period,
62and sometimes even helps crack the eggs with her snout at the end.
63These teeth-gnashing carnivores are softer than we think.
64Although these vicious creatures have attacked humans on a few occasions,
65the residents are not afraid of them.
66In fact, they show a great deal of reverence towards these wondrous creatures.
67Some say that crocodiles bring water to their habitat,
68so if they leave, they will bring the water with them.
69Obviously this is not true,
70but it demonstrates the admiration the inhabiting people have for crocodiles.
71Generally, crocodiles do not predate on humans.
72They attack when humans populate the crocodiles' habitat,
73instilling fear and uneasiness in the crocs.
74Like any other species, crocodiles are known to attack when feeling fear.
75There's still a lot more to be discovered about the African crocodile.
76Researchers want to know more about the population size,
77how many crocodiles inhabit Africa in all,
78how they form separate floats, etc.
79There is still also much to learn about migration patterns,
80and relations to other populations of crocodiles now found in other parts of the world.
81Next time, we'll examine a few specific case studies of crocodile populations in Southern Africa.