Download In the Wild - Maryland Zoo

Nile Crocodile: Crocodylus niloticus
In the Wild
Description:
The second largest species of crocodile after the saltwater crocodile
Size:
o Maximum size of about 20 ft (6 m)
o Average about 16 ft (5 m)
o The largest of the 4 species of African crocodiles
Weight:
o Can weigh up to 1,650 pounds (730 kg)
o Average about 500 pounds (225 kg)
Sexual dimorphism: Males are generally larger than females
Coloration:
o Juveniles are dark olive to brown with dark cross-bands on tail and body
o Adults are uniformly dark with dark cross-bands on tail
Habitat and Range:
Live throughout tropical areas of Africa, southern Africa, the Nile Basin and Madagascar
Primarily found in rivers, freshwater marshes and mangrove swamps
Some crocodiles may venture into larger bodies of fresh or salt water, but all must lay
their eggs on dry land
Diet:
Carnivorous: Mainly eat fish, but will eat almost anything, including zebras, small hippos,
porcupines, birds, antelope, domestic animals and other crocodiles
Are opportunistic, sit-and-wait hunters
o Hunt by lying concealed in the water until prey approaches – are capable of very
short bursts of high speed to catch prey, but cannot maintain speed to give
chase if the initial attack is unsuccessful
o Will scavenge carrion
o Flying prey can be caught by leaping into the air with thrusts of their powerful
tail
o Some larger individuals may also eat humans
Young will eat small fish and insects, larger individuals typically hunt larger prey
Can eat up to half its body weight at a single feeding
Prey is not chewed or ground in the mouth – teeth are only shaped for grasping prey
o Prey items are often swallowed whole
o If a crocodile wants to bite its prey into pieces, they must “death roll” around in
circles with the object in its teeth until smaller pieces break off
Adaptations:
Have very strong jaw muscles for biting and holding prey – jaws exert more than 2,000
pounds of pressure per square inch
07/25/2013
The Maryland Zoo in Baltimore
Nile Crocodile: Crocodylus niloticus
Are covered with non-overlapping scales composed of keratin (the same protein nails
and hair are made of) which are often studded with bony plates called scutes
o Heavy scales function as armor
o Scales are shed individually, not shed all at once as snakes do
o Scales do not provide much insulation, a feature which restricts all crocodiles to
tropical climates
Have a heavy, muscular tail
o Swim with back-and-forth movements of their tail – most of the time
crocodilians cruise slowly through the water, holding their legs against their body
to reduce drag
o Are also capable of great bursts of speed using their tail, including a "tail walk" in
which their head and body are held vertically out of the water
o Tail is also sometimes used for knocking large prey off-balance or into the water
Front feet have 5 separate toes which aid in digging nests and rear feet have 4 partiallywebbed toes which aid in swimming
Eyes and nose are positioned on the top of the head to allow for breathing and stalking
while almost completely submerged, allowing them to sneak up on prey
Have well-developed senses of smell, sight and hearing
o Ears are covered by flaps which close to prevent water from entering them
o Eyes are close together to allow for binocular vision to provide more accurate
depth perception
o Eyes are immobile spheres covered by three eyelids – the third eyelid, called a
nictitating membrane, is transparent but protects the eye from water
o Have vertical, cat-like pupils which dilate to allow them to see well in the dark
o A layer of tapetum at the back of their eyes greatly increases their ability to see
at night – also makes their eyes glow in the dark
o Do not see very well underwater
o Nostrils close when diving
o The nostrils are separated from the mouth by a bony palate (similar to
mammals, absent from other reptiles) and a valve in the back of the mouth –
allows for breathing when their entire body except their nostrils are submerged,
and also when holding prey
Have the most acidic stomachs recorded for any vertebrate, allowing them to digest
even the bones and shells of prey animals
o Digestion is also aided by a muscular gizzard containing stones to help break
down food
o Sometimes swallow stones to assist in digestion
Are able to survive for long periods of time without food – have been recorded surviving
for up to two years between meals
o Food is stored as fat in their tails, backs and elsewhere in the body – up to 60%
of the food intake may be converted to fat
o Are opportunistic hunters
07/25/2013
The Maryland Zoo in Baltimore
Nile Crocodile: Crocodylus niloticus
o Are ectothermic or “cold-blooded” – regulate their body temperature by using
the surrounding environment
Lifespan:
Typically live 40-80 years
Ecosystem relationships:
Normally solitary animals, but plentiful food may bring many individuals together
o When fish are migrating, may hunt cooperatively by forming a semi-circle across
a river and herding fish – they then eat the fish that are closest to them
o Even when large numbers congregate, they do not seem to fight over food –
when large prey is caught, another crocodile may help to dismember it, so that
the pieces are small enough to eat
Nile crocodiles are ecologically important as predators – keep populations of barbel
catfish, which are predators themselves, in check
o Barbels eat other fishes which are the diet of more than 40 species of birds
o If birds leave an area because there are no edible fish, the amount of bird
droppings, which provides nutrients for the fish, declines and the food chain is
disrupted
Reproduction:
Sexual maturity is reached once they reach a certain age and size – a small individual
may never reach sexual maturity even after they have reached the typical breeding age
Polygyny – males mate with more than one female but females only mate with one
male
In August and September, the female will dig a hole in a river bank or sandy river bed
and lay 25-100 eggs in nests made out of plant material and/or mud
The female will guard the eggs from predators during the 3 month incubation period
In November, 10-inch-long hatchlings emerge from the eggs – all eggs in a nest hatch at
the same time and the entire brood leaves the nest at once
The mother will often roll the eggs gently in her mouth to help hatching babies emerge
The sex of the hatchlings is determined by the temperatures in the nest
The mother carries hatchlings in her mouth from the nest to the water’s edge
Mothers will respond aggressively to hatchlings' distress cries
o If the hatchlings are in danger, the adult female may pick them up and flip them
into her mouth or gular (throat) pouch for protection
o The mother protects them until they are larger and less vulnerable to predation
– normally for several weeks after hatching
o Male crocodiles will sometimes guard the nest as well, though the fathers are
usually not involved in parental care
Newborns hunt insects and small fish – as they grow, they begin eating larger and larger
prey
Juvenile crocodiles can grow more than 12 inches per year
07/25/2013
The Maryland Zoo in Baltimore
Nile Crocodile: Crocodylus niloticus
Activity:
Nocturnal:
o Spend the night hunting in the water
o Leave water to bask in the sun around mid-morning – if the day is overcast, foggy
or misting , normally remain in the water longer
o In the hottest part of day, they may open their mouth to cool off
o Return to the water in the afternoon, before the air temperature begins to drop
Adults are territorial, and mark their territory by loudly slapping their head down on the
water or snapping their jaws on the surface of the water
o Dominant animals tend to swim higher in the water – other individuals
communicate their submission by swimming lower in the water
o Dominant animals control access to mates, choice nesting sites, food, basking
sites and living space
o During drought, territories are often forgotten as they crowd into the smaller
remaining inhabitable area, although hierarchies are still observed
Combat between crocodilians is rare, but does sometimes occur between animals of the
same size competing for dominance
o The two combatants line up next to each other facing opposite directions and
bang the sides of their heads together
o They also sometimes bite each other, but in either case they rarely cause any
lasting damage
Sometimes lie with their mouth open to allow African spur-winged plovers and
thicknees to pick parasites out of their mouth
Other “fun facts”:
There are three families of Crocodylia, with 23 species total
Mummified crocodiles and crocodile eggs have been discovered in Egyptian tombs
The teeth are not cemented into the jaw but simply attached to the outside and can be
broken off – can replace their teeth an indefinite number of times
Can outrun a person for short distances
Conservation Status and Threats:
The Nile crocodile is listed on CITES Appendix I
Listed on the IUCN Red List as Least Concern – may still be threatened in parts of its
range
Were hunted close to extinction in the 1940s – 1960s
o Local and international protections have resulted in significant recoveries in
several areas, and large populations can now be found in Botswana, Ethiopia,
Kenya, Zambia and Zimbabwe but it appears that numbers in central and
western countries are not recovering – this may be partly due to habitat
differences where humans come into conflict with Nile crocodiles, particularly in
Tanzania
07/25/2013
The Maryland Zoo in Baltimore
Nile Crocodile: Crocodylus niloticus
o To lower the demand for skins, many successful management programs have
been established in conjunction with CITES, particularly in Zimbabwe and South
Africa, with the emphasis being placed on ranching programs
o Countries which still have certain quotas that can be harvested from the wild,
such as Madagascar, are moving towards establishing their own ranching
programs
o The ranching initiatives are perhaps responsible for the lack of illegal trade in this
species, which is currently considered to be insignificant
Common threats:
o Were commonly hunted for their skin – the skin from this species is considered
to be a 'classic' skin, in that high-quality leather is obtainable without blemishcausing osteoderms reducing its value
o The proximity of much of their habitat to people means run-ins are frequent –
firm numbers are difficult to calculate, but estimates are that up to 200 people
may die each year in crocodile-related incidents
o In some regions, pollution, hunting and habitat loss have severely depleted their
numbers
o Entanglement in fishermen’s nets often cause drowning
o A non-native shrub (Chromolaena odorata) invades shoreline habitats in Greater
St. Lucia Wetland Park, South Africa and poses a threat of local extinction of Nile
Crocodiles – the shrub shades nest sites resulting in cooler nests than normal,
and since sex is determined by nest temperature, only females hatch
At the Zoo
Niles (male) is about 2 years old and weighs 3 lb. 5 oz. (1.51 kg).
What We Can Do
Make environmentally responsible lifestyle decisions to help conserve habitat –
conserve energy, reduce litter and pollution
Make sure you know the origin of the products you buy – opt for fake leather products
References:
http://animaldiversity.ummz.umich.edu/accounts/Crocodylia/
http://animals.nationalgeographic.com/animals/reptiles/nile-crocodile/
http://www.iucnredlist.org/details/summary/46590/0
http://www.philadelphiazoo.org/Animals/Reptiles/Crocodiles-Alligators/NileCrocodile.aspx
http://www.bronxzoo.com/animals-and-exhibits/animals/reptiles-andamphibians/nile-crocodile.aspx
http://library.sandiegozoo.org/factsheets/nile_crocodile/crocodile.html
http://www.seaworld.org/animal-info/animalbytes/animalia/eumetazoa/coelomates/deuterostomes/chordata/craniata/reptilia/cr
ocodylia/nile-crocodile.htm
07/25/2013
The Maryland Zoo in Baltimore
Nile Crocodile: Crocodylus niloticus
http://crocodilian.com/cnhc/csp_cnil.htm
http://www.buzzle.com/articles/biggest-crocodile-in-the-world.html
07/25/2013
The Maryland Zoo in Baltimore