Nile Crocodiles (Crocodylus niloticus & C. suchus) Fact Sheet: Reproduction & Development

Males display for females (from Modha 1967 unless otherwise noted)

• Splash display
• Tail arched upwards with tip touching the water
• Head and neck raised with the lower jaw touching the water
• Neck appears to swell
• Bubbles of water emerge on both sides of the male's body
• Male splashes water by lashing tail sideways and opening and closing the jaws
• Water "boils" near the snout and tail
• Male displays draw others near
• Other adults, presumably females, come from near and far towards the male
  • The male begins to follow one female

Courtship & Mating

• Partners perform courtship displays
• Male and female lift heads and rub jaws, gape the jaws widely, but do not bite
• When male and female begin to swim parallel, male may draw the female near with his forelimb, mount the female, and copulate
• Mating takes place in shallow water
• Larger females mate earlier in the season than smaller females and they mate with the largest males (Ferguson 1985)
• Interval between copulation and egg laying
• c. one month (Ferguson 1985)
• Up to 5 months reported by some (Pooley & Gans 1976)
• Suggests females store sperm until conditions are good for nesting
• Stressed females may retain eggs (Ferguson 1985)

Polygynous (from Britton 2003)

• Males take multiple partners
  • Short-term pair bonding has been described for Nile Crocodiles and other species
• Females may mate with multiple partners
  • Siblings known to have different fathers in some species of Crocodylus (Britton 2003)

Seasonal reproduction (from Britton 2003)

• Reproductive activity confined to several months per year
  • Clumped pattern of courtship, mating, and nesting
  • Nile Crocodiles usually breed once a year in South Africa. (Cott 1961) (Leslie et al 2001)
• Egg laying
  • Eggs laid between January and December, depending on rains and local climate (Ferguson 1985)
  • Ideally, eggs are in nest during last of dry season, hatching occurs at onset of rains (Cott 1975)

Nest Building

• Females build nests in dry season
  • Located near permanent water in areas with sandy soil (needed for digging)
    • River flats, lake-side beaches, sand-spits, dried up watercourses (Cott 1975)
    • Suitable nesting sites have shade in regions where air temperature might become excessively hot
  • Hole-type nest (not a mound)
  • Construction
    • Female digs hole with hind limbs and snout
• Nest characteristics
  • 40 by 60 cm (1.3 by 2 ft) in diameter (Ferguson 1985)
  • Depth, to 8 -18 in
    • Eggs typically buried 30-45 cm deep
  • Appears as an oblique burrow leading into a wide egg-chamber
    • After eggs are deposited, hole is filled in so that it is flush with surrounding ground and not obvious (Cott 1975)
    • On an island in Lake Rudolph, Kenya, Nile Crocodile females covered eggs with a mixture of soil and grass (Modha 1967)
• Female time at nest
  • Occupied with nesting and hatchling care for a total of nearly 6 months (Cott 1975)
• Communal nesting sites
  • Nests are often close enough to almost touch each other
    • More common in the past
    • Communal nesting much more difficult in modern times due to conflict with humans for these habitats
  • Female returns to same nest site year after year (Pooley & Gans 1976)

Clutch features

• Clutch size
  • 55-60 eggs
• Egg characteristics
  • Dimensions
    • c. 7.5 cm long (3 in)
  • Weight
    • c. 110 g (4 oz)

Incubation

• Temperature
  • Avg. temperature of 31°C (88°F)
    • Narrow range of optimal incubation temperatures — 28-34°C
  • Eggs incubated below 27°C (81°F) never hatch (Hutton 1987)
• Sex determined by nest temperature (from Rhodes & Lang 1996)
  • Clutches may be biased for one sex or another
    • Other species have slightly different temperature sensitivities
  • Half of all clutches are made up of both male and female offspring
  • Female neonates
    • Only females hatch at temperatures between 28°C and 31°C ( 82-88°F) (Hutton 1987)
  • Male neonates
    • Temperatures of 34°C (93°F) result in 81% male hatchlings
• Incubation time
  • Eggs are incubated 84 to 90 days
  • Nest humidity must be kept high for embryos to develop normally, either from a soil or plant cover, or local climate, or behavior of mother (urination, splashing water on nest)

Nest guarding

• Mother guards the nest
  • Watches nest for c. 10-14 weeks
  • Mostly by lying over the nest
  • Defends it against egg snatching predators
    • See nest predators in mortality section below
  • Female does not eat, or eats rarely while nesting

Hatching (from Ferguson 1985; Modha 1967; Pooley and Gans 1976; Cott 1975)

• Process of hatching
  • At time of hatching soil over eggs has become quite compacted
  • Baby crocodiles utter distress calls from within the egg below ground
    • Sound can be heard up to 20 m (ft) away
    • Females are strongly attracted to the calls and will make every effort to reach the nest if she's some distance away
  • Female moves soil off the nest to allow young to escape
    • A nest deserted by the mother will have young calling for several days; if the eggs then are unearthed the young burst from the eggs (Cott 1975)
  • Female opens mouth, depresses her tongue to make space, gathers hatchlings in her mouth, and moves from nest to nearby water where hatchlings are released by swinging her head from side to side
  • Young do not head for water on their own as do baby turtles; left to themselves, they seek a place to hide, even turning away from the water in that search
  • Male crocodiles have also been observed aiding in hatchling births by breaking eggs to free the young (rolls egg back and forth between his tongue and palate), a behavior which shows great muscular control and tactile sensitivity
  • Hatchlings placed near floating vegetation or a log fallen into water

Hatchling

• Hatchling characteristics
  • Size
    • Body measures c. 28 cm (11 in) long
    • Weigh c. 80 g (2.8 oz)
  • Growth & development
    • Young grow in length about 30 cm/yr (1 ft/yr) (Cott 1975)
    • Old crocodiles only grow around 2.5 cm/yr (1 in/yr)
• Hatchling behavior
  • Hatchlings from a single clutch stay together and are guarded by adult females and males
    • Often with members of other clutches
    • Young remain guarded for up to 3 months before dispersing
    • At end of clutch or crèche phase the young gradually disperse to areas where no adults or subadults are found

Juvenile 

• Development
  • While the young previously sought adult protection, now they avoid it.
    • Young crocodiles dig tunnels in river banks as shelter from predators and possibly to keep warm
    • Young use tunnels protection for their first five years
• Diet
  • Youngest crocodiles eat insects

Adult

• Sexual maturity
  • Males mature when over 9 ft in length; females 8 ft
  • Sexual maturity in managed care can be much younger than in wild (Ferguson 1985)
  • Sexual maturity at 12 to 19 yrs. in wild (Ferguson 1985)
• Peak reproductive years
  • Females:15-30 years

Wild populations

• Thought to be long-lived, though typical life expectancy not reported

Managed care

• No AZA estimates

Hatchling and juvenile mortality

• Fall prey to other animals
• Killed by crabs and large fish, other reptiles, herons and storks, and the mongoose and hyena (Pooley & Gans 1976)
• Nest predators (from Cott 1975; Ferguson 1985)
• Mammals
• Mongooses, water-mongooses, baboons, hyenas, warthogs, bush-pigs
• Birds
• Vultures, marabou storks
• Reptiles
• Varanid lizards like the Nile Monitor cause high egg mortality
• Flooding of the nest causes embryo death

Adult mortality

• Killed by humans
• Hippos
• Known to attack and kill adult crocodiles that threaten their calves (Cott 1975)

Image credit: © David Schenfeld from Flickr. Some rights reserved.

Bishop (2009)
Britton (2003)
Cott (1961)
Cott (1975)
Leslie (2001)
Ferguson (1985)
Hutton (1987)
Modha (1967)
Rhodes & Lang (1996)
Trutnau & Sommerlad (2006)