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Nile Crocodiles (Crocodylus niloticus & C. suchus) Fact Sheet: Behavior & Ecology

Activity Cycle

Active at day and night

  • Active at night, most often (Huchzermeyer 2003)
    • Spend night in water
    • Bask in the sun or cool off in the shade in daylight
      • Crocodiles use behavior (and physiological adaptations) to regulate body temperature (Seebacher et al 2003)
      • Winter activity pattern, in South Africa (Downs et al 2008; Kofron 1990)
        • Leave water to bask around 10 am
          • Remain in the water longer on overcast, foggy, or misting days
          • Researchers typically conduct census counts in the morning when animals are onshore
        • Return to water in afternoon
          • Before air temperature begins cooling
          • In hottest part of day may use mouth gaping to promote body heat loss (Cott 1975)
          • Temperature sensors implanted showed continuous variations in body temperature rather than reaching a preferred body temperature target

Resting behavior

  • Submerge in water for long periods
    • May remain underwater for up to two hours when not moving
      • Made possible because they are adapted to high levels of lactic acid in their blood (from Britton 2003)
        • Such lactic acid levels would kill other vertebrates
    • At the water surface, only the eyes, ears, and nostrils are exposed (Frey & Salisbury 2000)
  • Mouth gaping
    • Often rest with an open mouth
    • Behavior may help to reduce body or head temperature (Cott 1961; Loveridge 1984)
      • Some studies suggest it is used most often as a threat (Kofron 1990)
        • Gaping occurs at night and in winter, when the animals are not usually overheating
        • Kofron (1990) observed 45 threat displays using gaping in a sample of 54 observations of basking Nile Crocodiles in Kenya's Lake Turkana

Territory Size

Shoreline territories

  • Males defend bands of water and shoreline (from Modha 1967)
    • Shoreline stretches of c. 60 m (197 ft) in length
    • Possibly extending 50 m (164 ft) into the water,  study at Lake Rudolph in Kenya

Social Groups

Gregarious

  • Tolerate nearness of other Nile Crocodiles (Huchzermeyer 2003)
    • Use colonial nests in the wild (from Cott 1975)
      • Several crocodile families may use a suitable nesting area
      • Many former colonial nesting sites abandoned due to human interference
    • Females stay in nesting area to first guard nest, then to protect young
      • Males uncommonly guard hatchlings (Britton 2003)

Social hierarchy

  • Largest crocodiles are usually dominant
    • Dominance and territorial behaviors are not evident when the crocodiles congregate at basking sites in Gonarezhou National Park, Zimbabwe (Kofron 1990)
    • Other researchers observed dominant breeding bulls guarding their territories and basking separately in Kenya's Lake Turkana (Modha 1967; Cott 1961)
  • Sexes form separate dominance hierarchies
    • Males establish a dominance hierarchy as they fight to establish a mating territory (Pooley & Gans 1976)
    • Females establish hierarchies among themselves (Garrick & Lang 1976)

Territorial Behavior

Territorial

  • Males display some territorial behavior
    • Systematically patrol a territory (from Garrick & Lang 1976)
      • Behavior also noted for Crocodylus acutus which patrols along coastal habitats of the Caribbean Sea
      • American alligators (Alligator mississippiensis) in the southeastern U.S. do not patrol territories
    • Territorial male may chases out intruding males trying to mount females in their territory (from Modha 1967)
      • Do not attempt to "herd" or keep females within a territory
      • Intruding males that are sub-dominant usually swim away and come out on shore, followed by the snapping territorial male
        • The pursuing male half emerges from the water, roars, snaps at the fleeing male, and slides back into the water
      • Fights occur at times
        • Begin with a face off and vigorous hissing
        • May last up to 45 minutes; until one male swims away in defeat

Social Interactions

Aggression

  • Fights typically between males
    • Males receive many injuries in fights while establishing territories and access to females (Cott 1961)
  • Female aggression
    • Mothers become very aggressive when guarding hatchlings at the water's edge (from Cott 1975)
      • Known to attack humans and boats

Play

Uncommon (from Dinets 2015)

  • Object play
    • Toss objects, including food items, repeatedly into the air
      • May spin, jump, and splash around with the object
  • Social play
    • Young crocodiles (siblings) tussle/wrestle with one another

Communication

Complex systems of communication

Visual Signs and Displays

  • Signals adapted to open water habitats
    • In contrast to alligators' vocal signals that may be more advantageous in marshy, more closed habitats (Garrick & Lang 1977)
  • Sign of submission or appeasement (from Pooley & Gans 1976; Garrick & Lang 1977)
    • Snout lifting
      • Behavior performed by subordinate males
        • Also made by females to all males
          • By comparison, female American Alligators pair bond without any submissive behavior by either sex (Garrick & Lang 1977)
      • Raise the head to expose the throat
  • Aggressive signals (from Britton 2000 unless otherwise noted)
    • Mouth gape
      • Function possibly for social signaling to others as well as having a cooling function (Kofron 1990)
    • Inflate (puff up) the body
    • Lunge
      • Generally short movements of the body
      • Males first challenge intruders in their territory by lifting the head and arching the tail
        • Chases, lunges, mock or real fighting may follow (Garrick & Lang 1977)
    • Bite
    • Threat vocalizations often accompany such displays
  • Courtship displays (from Modha 1967 unless otherwise noted)
    • Males display in dramatic fashion
      • Splash display
        • Jaws smacked on water's surface, producing a loud noise
      • Fountain display
        • Snout held below the water, air expelled through nostrils
        • Produces a jet of water



Vocalization

  • Crocodiles are highly vocal
    • Young vocalize even before hatching (Campbell 1973)
      • Call up to 30 minutes before hatching
      • May help coordinate hatching or serve to call for adult assistance in digging open the nest, and in helping break open the eggs
      • Hatchlings appear to actively seek adult's attention after hatching
        • Perhaps to be picked up and transported to water
        • Hatchlings in adult's mouth continue to call, possibly with less intensity, which may ensure they aren't swallowed (Pooley & Gans 1976)
          How does the hatchling get air while making in-the-egg vocalizations? Some researchers speculate by using the egg tooth to tear the inner membrane of the egg, allowing air to diffuse through the porous shell.
    • Juvenile vocalizations
      • Serve to help young communicate with siblings and adults (Britton 2001)
      • Threat calls
        • Larger juveniles make a hiss much like the adult call that confronts an intruder
  • Adult calls
    • Threat hisses
      • Often accompany visual signals (gaping, body inflation, short lunges, and attempts to bite)
    • Annoyance calls
      • Loud, high intensity vocalizations
      • Perhaps in attempt to intimidate an attacker
    • Distress calls
      • Acoustic signal is similar to hatchling calls, though much louder and longer in duration
        • Serve to attract other adults (male and female) and warn nearby juveniles
        • Adults that respond to a distress call may produce a responding call and rush to drive away a predator (Romero 1983; Trutnau & Sommerlad 2006)
    • Roar
      • Loud sound given by territorial males roar to attract females
    • Female specific calls (from Trutnau & Sommerlad 2006)
      • Mother vibrates muscles around her rib cage to warn young of danger
        • Young respond by diving into the water

Olfaction/Scent Marking

  • Good sense of smell
    • Detect prey by smell (Pooley & Gans 1976).

Locomotion

Aquatic movements

  • Travel through the water most often
  • Swimming
    • Move quickly through the water
      • Torpedo-shaped body reduces drag (Trutnau & Sommerlad 2006)
    • Strong tail provides main forward thrust for swimming
      • Capable of launching the body out of the water in pursuit of prey (Trutnau & Sommerlad 2006)
    • Propulsion achieved by a undulating wave from head to tip of tail
    • Front limbs are tucked under body; hind limbs drag behind
  • Diving (from Frey & Salisbury 2000)
    • Slowly withdraw the body backwards, most often
      • From a floating position, release air from nostrils and mouth and sink down gently
      • Also powered backwards dive with help from hind limbs and tail
    • Forward diving is rarely observed
  • Bottom walking (from Frey & Salisbury 2000)
    • Frequently used in shallow water

Terrestrial movements

  • Become exhausted easily on land
  • High walk
    • Body held off the ground with the legs and tail
      • Do not drag body across ground, crawling like most lizards
    • Legs erect under the body and tail dragging
    • Achieve speeds of c. 3 km/h (1.9 mi/h)
  • "Run" with a sprawling gait
    • Faster movement
    • Front and rear limbs coming together on one side as the body curves in that direction
  • Gallop (from Webb and Manolis 1989; Cott 1975)
    • Fastest form of terrestrial movement
      • Reach speeds of 18 km/hr (11mi/hr) for short distances
    • Front limbs moving out and forward as hind limbs thrust the body forward
      • Resembles bounding run of squirrels
    • Typical in the young of some crocodile species

Interspecies Interactions

Interactions with hippos (from Cott 1975; BBC Wildlife 2009; Kofron 1990)

  • Hippos are dominant, most often
    • Hippos may push aside a crocodile basking on land or knock it into the water
    • A female hippo with a calf or others in the herd will drive out all crocodiles from their pool of water
      • Crocodiles are killed by hippos if they stray too close to hippo calves

Animal associates (Cott 1975)

  • Several birds associate with the Nile Crocodile
    • Spurwing Plover (Uganda) and Water Dikkop (Uganda, South Africa) make shrill alarm calls to which crocodiles respond
    • Plovers have also been reported to enter crocodile mouths to clean off parasites
    • Common Sandpiper, Egyptian Plover (Egypt), and Blacksmith Plover (Zambia) pick ectoparasites from the crocodiles
  • African Softshell Turtles (Apalone) (from Trutnau & Sommerlad 2006)
    • Lay their eggs near Nile Crocodile nests
    • When female Nile Crocodiles carry their young safely to water after hatching, they also may carry young turtles that have synchronized their hatching to that of the young crocodiles

Humans

  • Nile Crocodiles kill many humans (from Crocodile Specialist Group 1996)
    • Cause more human deaths than any other crocodile species
    • In Zimbabwe they cause more human fatalities than do all other animals combined

Fishing

Nile Crocodile fishing

Image credit: © Steve Garvie from Flickr. Some rights reserved.

Page Citations

BBC Wildlife Magazine (2009)
Britton (2001)
Britton (2003)
Campbell (1973)
Cott (1975)
Cott (1975)
Crocodile Specialist Group (1996)
Dinets (2015)
Downs (2008)
Frey & Salisbury (2000)
Garrick & Lang (1977)
Huchzermeyer (2003)
Kofron (1990)
Loveridge (1984)
Modha (1967)
Modha (1968)
Pooley & Gans (1976)
Romero (1983)
Seebacher et al (2003)
Spotilla et al (1977)
Trutnau & Sommerlad (2006)
Webb & Manolis (1989)

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