Dwarf Crocodile (Osteolaemus tetraspis) Fact Sheet: Reproduction & Development

Courtship & Mating

• Male reproductive behaviors (summarized in Waitkuwait 1989 unless otherwise noted)
  • Male-female interactions
    • Males produce low-pitched and resonant drumming vocalization (from Beck 1978)
      • Individuals in managed care drum c. 2 months prior to the female laying eggs
      • Drumming often continues throughout the night (Helfenberger 1981)
    • Mates participate in neck rubbing
      • Partners rub one another’s head and jaw
  • Male-male interactions
    • Males engage in bouts of fighting

Reproduction

• Seasonal reproduction, Cote d’Ivoire (from Waitkuwait 1989)
• Nest construction begins at the end of the dry season
• Period associated with an abundance of fallen leaves needed to build nests
• High rainfall amounts experienced during the subsequent nesting period
• Period extends > 274 days
• Not uncommon for nest construction to occur outside the nesting period
• c. 1 in 3 nests built at other times of the year
• Mound nesters (from Waitkuwait 1989 unless otherwise noted)
• Nest structure
• Mounds of leaves and rotting vegetation
• Decomposition believed to release heat and aid embryo development
• Four sided structure
• Flat on two sides and steeply sloped on the remaining sides
• Furrow across the top created by the female lying on the nest or creeping over it
• Dimensions highly variable
• Likely vary according to environmental temperature
• Nest size and structure are strongly influenced by the materials available to mothers
• Nest construction
• Female builds the nest
• Forelimbs collect materials from a few meters surrounding the nest area
• Debris is typically pushed against the base of a tree (Eaton 2010a)
• Nest site placement
• Not located immediately next to water
• Average distance from water 16.9 m (55.4 ft)
• Height above water table
• Placed 1-2 m above the water line (Riley and Huchzermeyer 1999)
• Maternal nest guarding (from Waitkuwait 1989)
• Visit and guard nest during incubation period
• Interbirth interval (time between consecutive births)
• Annual reproduction (Waitkuwait 1989; Hara and Kikuchi 1978)
• 1 clutch per season is typical; rarely 2 (Trutnae and Sommerlad 2006)

Clutch characteristics (from Hara and Kikuchi 1978 unless otherwise noted)

• Clutch size
  • Mean clutch size 10-14 eggs (Waitkuwait 1989, Eaton 2004)
  • Range 6-17 eggs (Beck 1978; Groombridge 1982; Waitkuwait 1989)
• Egg features
  • Elliptical in shape
  • White, smooth appearance
    • Yolk slightly visible through the shell for a few days
      • Fertile eggs are distinguishable from unfertilized ones
    • Become opaque and more rigid within several days
• Egg dimensions
  • c. 69 x 37 mm (2.7 x 1.5 in) (Waitkuwait 1989)
  • Broad ranges reported in a population raised in managed care
    • 60.9-70.5 mm x 39.0-42.7 mm (2.4-2.8 in x 1.5-1.7 in)
• Egg weight
  • 56.7-70.5 g (2.0-2.5 oz)

Incubation & Hatch

• Incubation (from Waitkuwait 1989)
  • Length of incubation
    • Variable
      • c. 100 days
      • Breeding in managed care: 68-126 days (Hara and Kikuchi 1978; Sims and Sing 1978; Waitkuwait 1989)
  • Incubation temperature and humidity
    • Nest mound temperature range of 26-34^oC
      • c. 5^oC higher than ambient
    • Minimal fluctuation in humidity and temperature within a single nest
      • <0.5^oC
      • Air space of the egg chamber almost always at saturation point
  • Sex determination and incubation (from Trutnae and Sommerlad 2006)
    • Temperature and timing determine gender among crocodilians
      • No published reports on the influence of temperature on sex determination in Dwarf Crocodiles
      • Many other crocodilian species produce females at lower incubation temperatures; in some, females are produced at high and low incubation temperatures and males at mid-range temperatures
• Hatching
  • Process of hatching (from Waitkuwait 1989 unless otherwise noted)
    • Cracks develop on eggs a few days prior to hatch
      • When inside the egg, young vocalize by croaking heavily when movement occurs in the nesting area
    • Mother reacts to calls of young by excavating the nest to assist hatching
      • Mother gently holds the partially emerged neonate within her jaw and rolls it until the eggshell is removed
      • Once free, she transports the neonate to the water, held within her mouth
      • Female West African dwarf crocodile helps hatchling from the egg video (Crocodiles of the World)
    • Typically emerge 1-2 days after the appearance of the first crack, observation in managed care (Hara and Kikuchi 1978)
      • Longer intervals possible (Hara and Kikuchi 1978)
  • Hatchling characteristics
    • Size
      • Body mass
        • 43.5-51.1 g (1.5-1.8 oz) (Hara and Kikuchi 1978)
      • Length
        • Mean total length:
          • 279.3 mm (11 in), one study of wild crocodiles (Waitkuwait 1986); 180-223 mm (7.1-8.8 in) (Eaton 2004)
        • Managed care bred hatchlings variable in size
          • Total length: 199-238 mm (7.8-9.4 in) (Hara and Kikuchi 1978)
          • Snout-vent length: 105-124 mm (4.1-4.9 in) (Hara and Kikuchi 1978)
    • Appearance (from Beck 1978)
      • Boldly colored
        • Back dark, nearly black
          • Predominant color interspersed with irregular, creamy yellow cross bands
        • Belly light
          • Graduates to an intense yellow on the jaw
• Interbirth interval
  • Annual reproduction (Waitkuwait 1989; Hara and Kikuchi 1978)
    • 1 clutch per season is typical; rarely 2 (Trutnae and Sommerlad 2006)

Hatchling (from Waitkuwait 1989 unless otherwise noted)

• Care
  • Mother (and possibly father) remains near young to provide protection for some time (Eaton 2004)
    • Young call (vocalize) to mother
  • In managed care, male known to be involved in care, similar to female (Trutnae and Sommerlad 2006)

Adults

• Mature c. 5 years of age (from Waitkuwait); estimated maturity 6.8 – 15.7 years(Eaton 2011)
  • Reach maturity at approx. 1 m (39.4 in) in length (Kofron and Steiner 1994; Eaton 2011)
  • Growth continues after reaching sexual maturity
• No evidence of reproductive senescence
  • Offspring fathered by male >67 years of age in managed care (ZIMS 2015)

Wild populations

• Not reported

Managed care

• Commonly survive > 40 years (ZIMS 2015)

Predation

(from Waitkuwait 1989 unless otherwise noted)

• Humans are the primary predator of Dwarf crocodile (Thorbjarnarson and Eaton 2003)
• Natural predators
  • Hatchlings are most susceptible
  • Present at low density in tropical forests
    • Do not likely represent a threat to crocodile populations

Juvenile dwarf crocodile (Osteolaemus tetraspis) in the Ankasa Resource Reserve, Ghana.  Image credit: © Francesco Veronesi at Flickr. Some rights reserved.