Dwarf Crocodile (Osteolaemus tetraspis) Fact Sheet: Behavior & Ecology

Nocturnal

Activity patterns

• Hunt at night
  • Search for prey along well-defined trails in the forest (Riley and Huchzermeyer 1999; Riley and Huchzermeyer 2000)
    • Thought to be one of the most terrestrial crocodiles (Waitkuwait 1989)
• Rest in the water during daylight (from Frey and Salisbury 2001 unless otherwise noted)
  • Hide in small pools or deep burrows (Eaton 2010a)
  • Resting behavior
    • Hold body raised off the streambed
      • Tips of toes support the body in shallow water
      • In deeper water, the forelimbs lose contact with the ground and are held at the sides
        • Body floats at an angle to the water surface when water depth exceeds body length
    • Eyes, ears, and nostrils protrude above the water surface
    • Body posture similar to those of alligators, crocodiles, caimans, and gavials

Home range studies have not been thoroughly conducted among wild populations.

Sometimes seen in pairs (Wild 2000) and ostensibly in family groups (Eaton 2004)

Typically segregate as individuals, in Cameroon (Wild 2000)

• Tree-falls form slow backwater areas where individuals are found

Studies of territorial behavior have not been thoroughly conducted among wild populations.

Aggression

• Few studies of aggression in this species
  • Wounded or severed tails suggest aggressive interactions, in both the wild (specifically Gabon) and managed care individuals (Pauwels et al. 2007; Trutnae and Sommerlad 2006)

Vocalization (from Dinets 2013 unless otherwise noted)

• Moan, groan, and roar
  • Often preceded by a characteristic “head oblique tail arched” body position
    • Head and tail held above the water surface; body straight and below the water
      • Tail arches over the body
• Croak
  • Sound young make while in the egg (Waitkuwait 1989)
• Infrasound
  • Strictly a male vocalization
  • Non-vocal vibration normally produced below the water surface
    • Frequency below the range of human hearing (c. 10 Hz)
  • Visually detected by the “water dance” effect
    • Visible ripples on the water surface; small droplets jump up off the water
• No reports of head slapping

Olfaction/scent marking (from Weldon and Wheeler 2001)

• Secretory glands believed to secrete pheromones
  • Similar glands present in all extant (living) crocodilians
  • Function unclear
• Age class variation in the chemical composition of secretions
• See more on secretory glands in Adaptations

Terrestrial movements

• High walk (from Brinkman 1980 unless otherwise noted)
  • Belly held off the ground; legs swung beneath the body
    • Common form of terrestrial locomotion among crocodiles
  • Limbs move in a trotting gait (Reilly and Elias 1998)
    • Diagonal pairs of legs move forward at the same time

Aquatic movements (from Frey and Salisbury 2001 unless otherwise noted)

• Swimming
  • Paraxial swimming
    • Limbs propel the body through the water
      • Backward limb movement provides thrust
        • Stronger, larger hindlimbs provide more thrust than the forelimbs
      • Diagonal pairs of legs move forward at the same time
  • Axial swimming
    • Tail propels the body through the water
      • Tail undulates laterally to provide thrust
      • Forelimbs under the body (Trutnae and Sommerlad 2006)
      • Hindlimbs relaxed and dragging (Trutnae and Sommerlad 2006)
      • Paraxial and axial swimming may be used simultaneously to produce a hybrid motion
    • Fastest form of aquatic movement
    • Similar to the swimming style of other crocodilians
  • Steering
    • Hindlimbs direct movements through the water
• Diving
  • Sink backward and downward, below the water surface
    • A gentle motion produced by movement of the hind limbs and tail
      • Hind limbs simultaneously drawn toward the head
      • The back half of the tail is swept laterally toward the head
• Bottom walking
  • Body held close to the substrate (Frey and Salisbury 2001; Reilly and Elias 1998)
  • Femur of the hindlimbs moves horizontally to the body (Brinkman 1980)
  • Limbs move in a trotting gait (Reilly and Elias 1998)
    • Diagonal pairs of legs move forward at the same time
• Tail walking
  • Tail propels the body vertically out of the water
    • Ambush technique used to surprise and seize prey on tree branches overhanging the water
  • Similar movements produced by other crocodilians, such as the American Alligator

Other Behaviors

• Basking
  • Bask in sun for only brief periods, less than an hour long (Groombridge 1982; Trutnae and Sommerland 2006)

Interspecific Interactions

• Predators (from Waitkuwait 1989 unless otherwise noted)
• Potential predators of eggs and juveniles
• Reptiles: Nile Monitor, Soft-shelled Turtles, Rock Python (Riley and Huchzermeyer 1999; Somaweera et al. 2013; Waitkuwait 1989)
• Monitors known to prey upon nests
• Mammals: otters, water mongoose, tree civet, genets, leopard, and golden cat
• Birds: herons and various birds of prey
• Invertebrates: ants
• Colonize nests and destroy entire clutches of eggs; also known to kill hatchlings (Somaweera et al. 2013)
• Competitors
• Other crocodiles (from Kofron 1992)
• Minimize direct resource competition through habitat partitioning
• Nile Crocodile exploits larger river sections, mangrove swamps, coastal lagoons, and river mouths
• Survives in regions with brackish (saltier) waters
• Slender-snouted Crocodile exploits larger, fresh-water rivers and lakes in rain forests
• Dwarf Crocodile utilizes small streams, pools and swamps within rain forests
• Nile Monitor (Varanus niloticus)
• Large degree of overlap in diet and habitat (from Luiselli et al. 1999)
• Dwarf Crocodile consumes a wider variety of prey items than Nile Monitors
• Symbiotic relationships
• Parasitic interactions (from Riley and Huchzermeyer 2000)
• Endoparasites
• Larval crustaceans known to infect the lungs
• Three species of pentastomids commonly found in specimens taken in the northern Congo Republic
• Consumption of infected fishes likely leads to infection
• High rate of infection in some populations

Dwarf Crocodile (Osteolaemus tetraspis). Image credit: © Mitchell Eaton at IUCN Crocodile Specialist Group.  All rights reserved. Reproduced with permission from the artist.