Department of Environment and Heritage Protection
Junior Ranger program
Lesson Plan
Introduction to crocodile awareness
Purpose
This activity aims to introduce students to crocodile awareness. It draws on prior knowledge students may have
about crocodiles and promotes discussion around the topic of crocodile biology, behaviour and management of
the species.
Links with the Australian curriculum
This activity is suitable for a broad range of year levels and is designed to provide students with background
knowledge prior to receiving talks from crocodile experts conducting research in the community.
Year 5 Science: Science understanding/Biological sciences
Living things have structural features and adaptations that help them survive in their environment.
Year 6 Science: Science understanding/Biological sciences
The growth and survival of living things are affected by the physical conditions of their environment.
Year 7 Science: Science understanding/Biological understanding
Interactions can be described in terms of food chains and food webs; human interactions can affect these
interactions.
Introduction
Estuarine crocodiles are key predators and a crucial link in the food chain in tropical wetland areas. Students living
in communities near crocodiles should have some knowledge of crocodile behaviour and preferred habitat. Making
use of existing knowledge of estuarine crocodiles will help prepare students for subsequent visits and school talks
from crocodile experts, such as land and sea rangers or researchers from Australia Zoo.
Read the background information on crocodile ecology and biology before engaging classroom discussion.
Activity: Fact or fiction
Print out enlarged versions of the statements in the table on the next page and have students discuss whether
each statement is fact or fiction. Students can then attach each statement to the appropriate ‘fact’ or ‘fiction’
column. Statements may need to be adapted to suit the age group of students.
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Read the background information provided below and the suggested links for more information on crocodiles.
Further to the classroom discussion, have students develop a list of questions they can ask visiting
crocodile experts.
Your class can add its own topics to the fact or fiction debate, some examples of which are below:
• You should never smile at a crocodile.
• Large crocodiles should be removed from the environment (debate the role that large crocodiles play in the
ecosystem and assess this against the potential danger to humans).
• You should report all crocodile sightings to local land and sea rangers.
• It is not safe to swim in any tropical waters.
Fact
Fiction
Crocodiles have salt glands on their tongues to remove
excess salt in their blood.
Crocodiles need to eat three times a day, especially in
winter.
Large crocodiles are key predators in the environment.
Australia has only one species of crocodile.
A crocodile can stay underwater for more than three hours.
A crocodile will drown if it opens its mouth underwater.
Crocodiles fight each other and will eat smaller crocodiles.
Crocodiles have a poor sense of smell and hearing.
About half of a crocodile’s length is made up of its tail.
Crocodiles are stupid, even by reptile standards.
Crocodiles have been on Earth since the time of dinosaurs.
Crocodiles only hunt by waiting and ambushing prey.
Small crocodiles eat insects (especially grasshoppers) as
well as frogs and small animals.
It is okay to feed wild crocodiles.
Crocodiles are reptiles and lay eggs.
Crocodiles do not guard their eggs.
Favoured meals for crocodiles include mud crab, barramundi
and turtle. Feral pigs are also a key part of their diet.
Estuarine crocodiles are only found in Australia.
It is thought that crocodiles swallow rocks (gizzard stones)
to aid digestion and control buoyancy.
It is okay to stand in the water as long as you do not visit the
same place three days in a row.
Crocodile skin has bone in it.
It is safe to scoop water by leaning over the water’s edge
from low tree branches.
Crocodiles can live to be over 70 years old.
Crocodiles only hunt at night.
Rangers monitor crocodile populations for future
management of the species and to protect the community
and visitors.
Crocodiles make good pets.
Crocodile research helps scientists and rangers to better
understand wild populations.
Crocodiles only attack visitors and never locals.
Crocodiles have cultural significance to Aboriginal people.
Crocodiles are only found in rivers and never in the ocean.
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Background information
Estuarine crocodiles are widespread from India to northern Australia. Outside Australia crocodiles are largely
considered to be endangered, with Australia representing their last stronghold. Also known as the saltwater
crocodile, or ‘salties’, their scientific name is Crocodylus porosus.
Freshwater crocodile (Crocodylus johnstoni) are also found in Australia. Sometimes called ‘freshies’, they are
considered harmless if left alone. Do not be fooled by their common names though; ‘salties’ are quite happy
spending their time in freshwater and ‘freshies’ are known to live in estuaries.
Crocodile management
Crocodiles are protected wildlife but they are also managed to ensure problem crocodiles do not cause an
unacceptable safety risk to human populations. There are four basic principles to crocodile management:
1. Protect humans from crocodile attack.
2. Conserve viable populations of estuarine crocodiles in the wild.
3. Minimise loss of stock and aquaculture from crocodile attacks.
4. Ensure the commercial use of estuarine crocodiles is ecologically sustainable.
Interesting senses
• Taste—Animals that live in salty environments absorb salt through their skin and swallow salt when they eat.
Crocodiles remove excess salt through salt excretory glands.
• Sight—crocodiles see underwater just as well as they see above the water. They also have very good vision both
in broad daylight and in the dark.
• Smell—crocodiles have a good sense of smell and use this sense to find carrion. Relocated crocodiles will return
home, sometimes travelling great distances, by using senses relating to animal homing instincts that we don’t
yet fully understand.
• Hearing—crocodiles can use their sense of hearing both above and below the water. They can easily hear and
sense the sound of boats and potential prey or predators walking on river banks. Crocodiles are hard to surprise
because they can hear and sense you coming a long way off. Rangers need to be skilled at controlling the
approach speed of boats when monitoring crocodiles.
• Touch—there are pressure receptors in the upper and lower jaws of crocodiles that can detect vibrations in the
water as well as movement on the banks. Crocodiles can sense fish and other potential prey in murky water at
night—no wonder they have been around since the days of the dinosaurs!
Crocodiles also have ossified dermal scutes on their back, which are modified scales reinforced with bony material
that act as armouring. The scutes also assist in making them hydrodynamic, meaning they can move through the
water without making a ripple.
Hunting strategies
The crocodile brain is well advanced for a reptile and they find clever ways of sneaking up on prey. As active
predators, crocodiles use ambush tactics and opportunistic scavenging. For example, crocodiles will visit boat
ramps to scavenge fish frames left by careless boaties and they are known to take the last animal in a group
crossing a river. They have been recorded following the tracks of nesting turtles so they can prey upon adult turtles
as they nest. Crocodiles also ambush female turtles returning from nesting sites as well as hatchlings as they enter
the water for the first time.
Juvenile crocodiles eat insects and small animals, especially insects that live in vegetation along the water’s edge,
like grasshoppers and spiders. Crocodiles can also explosively launch their body out of the water to grab fruit bats
and birds perched on low branches overhanging the water.
As crocodiles do not have fleshy lips to control water intake, they are able to seal off their throats to prevent
swallowing too much water when submerged. This is called the palatal valve, and is the reason crocodiles cannot
swallow underwater.
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Lifecycle Crocodiles are reptiles and are well adapted to a semi-aquatic lifestyle. Female crocodiles make a nest out of
compostable material on the water’s edge. They lay between 30 and 70 eggs in the nest over the wet season.
Crocodile embryos do not have sex chromosomes (as mammal embryos do); it is the temperature within the
nest that determines the sex of the young. Males are produced if incubated within the temperature range of
31–32 degrees, whereas females will develop if eggs are above or below this temperature.
The variation of temperature in the nest and between other nest sites means there is a mix of males and females
across the population. Eggs within the same nest site hatch at the same time despite the different temperatures
found in the nest. It is thought that chemical cues and vocalisation help ensure that all the baby crocodiles hatch
at the same time. Synchronised hatching can reduce opportunistic predation that would otherwise occur due to
odours released by new hatchlings and the remaining egg contents. Turtles also use this strategy.
Even though they have no vocal chords, crocodiles still make use of sounds to communicate. Acoustic
communication is a particularly important aspect of parental care—for example, juveniles can make a squeaky bark
to which the female parent will respond energetically. Adults sometimes vocalise during courtship, while adult
females may make maternal growls to recall juveniles, and all crocodiles can hiss as a defensive noise.
The female crocodile will often guard the nest. Male crocodiles can be territorial, but are most defensive of females
during the breeding season.
Decades ago crocodiles were hunted to near extinction but were protected under Queensland legislation in 1974.
They are listed as a vulnerable species under Queensland’s Nature Conservation Act 1992. Crocodile populations
are now recovering in some areas.
Crocodile distribution in Queensland is constrained to the northern part of Queensland, with populations reaching
as far south as just north of Rockhampton. However, on occasions a displaced individual crocodile has been
recorded as far south as the Logan River near the Gold Coast.
Extension activities
• Crocodiles have cultural and social significance to Aboriginal and Torres Strait Islander people. Ask Elders in
your community about the importance of crocodiles to them. Record this information in multimedia format, such
as a video presentation.
• Ask local land and sea rangers to show your class photos of crocodile nests (this is safer and more comfortable
than visiting a nest in person). Make notes in your junior ranger field journal. What does the nest look like? How
does the design reflect the crocodile’s adaption to the environment? Draw a cross-section of a crocodile nest.
Compare the design to other reptile nesting sites. • Discuss tracking data with Australia Zoo staff and local land and sea rangers. As a class discuss what
behavioural patterns can be discerned from the tracking data.
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• Ask land and sea rangers and Australia Zoo staff about the lifecycles of crocodiles. Draw a crocodile lifecycle
diagram. Add the timing of lifecycle events to your seasonal calendar http;//www.ehp.qld.gov.au/ecosystems/
community-role/ranger/junior/pdf/seasonal-calendar-lesson-plan.pdf. Why do you think crocodiles breed at
this time of year? Think about temperatures, flooding, food availability and other factors.
• Develop a poster to educate visitors to the community about being ‘croc wise’.
• Produce a map of the local area detailing locations where crocodiles have been reported and describe areas
where crocodiles are able to live.
• Map out the food chain and design a food web for the lower estuarine reaches of a tropical river system. Include
mangroves, mud crabs, mullet, barramundi and large and small estuarine crocodiles.
• Produce a photo-book detailing how land and sea rangers manage crocodile populations.
• Write a story about a day in the life of a crocodile from the point of view of the crocodile (remember that
crocodiles are active at night too).
• Design a menu for a restaurant that caters to crocodiles (don’t forget the kiddies menu). Also come up with a fun
name for the restaurant (The Krusty Krab is already taken).
• As a class, write a song about a crocodile and a turtle to the tune of ‘Monkey and the Turtle’ (or your favourite song).
Additional resources
Removal of crocodiles:
http://www.ehp.qld.gov.au/wildlife/livingwith/crocodiles/crocwatch/2012-archive-resolved.html
Homing instincts of crocodiles (Wenlock River example):
http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0000949
General information on crocodiles:
http://www.ehp.qld.gov.au/wildlife/livingwith/crocodiles/index.html
and
http://www.kingsnake.com/oz/crocs/porosus.htm
Croc wise brochure:
http://www.ehp.qld.gov.au/register/p01101aa.pdf
Australia Zoo:
http://www.australiazoo.com.au/our-animals/amazing-animals/reptiles/?reptile=crocodilians
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